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Emergency obstetrical ultrasonography
Emergency Obstetrical Ultrasonography Peter M. Doubilet and Carol B. Benson
HE TERM "emergency obstetrical ultrasound' comprises two types of situations involving obstetrical sonography. First are cases where sonography is performed on an emergency basis to evaluate acutely symptomatic pregnant patients, such as those with pelvic pain or vaginal bleeding. When the symptomatic patient is in the first trimester of pregnancy, the role of sonography is to distinguish among a failed (or failing) intrauterine pregnancy, an ectopic pregnancy, and a normal ongoing intrauterine pregnancy. When the symptomatic patient is in the second or third trimesters of pregnancy, the main diagnostic considerations are placenta previa and placental abruption. The second type of emergency obstetrical ultrasound study is one that demonstrates a finding requiring emergent management, such as unexpected cervical dilatation. With either type of emergency sonogram, the ability to make rapid and accurate diagnoses can improve outcome and relieve parental uncertainty and anxiety.
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ULTRASONOGRAPHY OF THE ACUTELY SYMPTOMATIC PREGNANT PATIENT
First-Trimester Bleeding or Pain Role of Ultrasonography in Diagnosis. When a patient presents with a positive pregnancy test and symptoms of vaginal bleeding or pain, she is at elevated risk for having an abnormal pregnancy, including a failed or failing intrauterine pregnancy (IUP) or an ectopic pregnancy. However, bleeding may also occur in an otherwise normal, ongoing IUR Ultrasonography is the primary diagnostic modality for distinguishing among these possibilities. The key to accurate sonographic diagnosis in the symptomatic patient is an understanding and recognition of normal sonographic findings in early pregnancy. Transvaginal sonographic norms for gestational age, serum beta-human chorionic gonadotropin ([~-HCG), and other factors have been established. In a normal pregnancy, a gestational sac is identifiable at 5.0 weeks gestational age 1,2 (using "gestational age" synonymously with "menstrual age"), a yolk sac can be seen within the gestational sac at 5.5 weeks, 3 and cardiac activity is visible at 6.0 weeks. 1,3 A gestational sac can often be seen when the [3-HCG is 500 to 1,000 mIU/mL
and is consistently identifiable when the [3-HCG is > 1,000 mIU/mL. 3 (These values apply to the First and Third International Reference Preparations, and should be halved for the Second International Standard3). When a gestational sac is seen, a yolk sac should be visible within it when the mean gestational sac diameter is ->8 ram, and an embryo should be seen when the mean sac diameter is -> 16 ram. 4 Cardiac activity is always identifiable in a living embryo whose crown-rump length (CRL) is ->5 mm and is most often seen in even smaller embryos. 5,6 The normal heart rate is ->100 bpm before 6.3 weeks and -> 120 bpm at 6.3 to 7 weeks. 7 Most of these norms, or milestones, of early pregnancy should be taken as general guidelines and not as rigid rules, in that a pregnancy that misses a milestone may prove to have a normal outcome. 8,9 For example, although a woman whose sonogram demonstrates an intrauterine gestational sac with mean sac diameter of 8 mm mad no detectable yolk sac will generally prove to have an abnormal pregnancy, there is a chance (albeit small) that she will subsequently be shown to have a normal pregnancy and have a good outcome. 9 When a sonogram is performed in a symptomatic patient in the early first trimester, the diagnosis hinges on the answers to three questions (Fig 1): Does the sonogram demonstrate an intrauterine gestational sac? If so, are the gestational sac contents normal? Are the adnexa normal in appearance? Each of these questions bears further scrutiny. When deciding whether an intrauterine fluid collection represents a gestational sac, care must be taken not to mistake blood or other fluid in the uterine cavity for an IUP. To avoid this error, a gestational sac should be diagnosed only if a fluid collection in the uterus contains an embryo or yolk sac or if it is surrounded by two echogenic rings ("double sac" or "double decidual ring" sign) (Fig 2). l°
From the Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA. Address reprint requests to Peter M. Deubilet, MD, PhD, Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115. Copyright © 1998 by WB. Saunders Company 0037-198X/98/3304-000558.00/0
Seminars in Roentgenology, Vol XXXIII, No 4 (October), 1998: pp 339-350
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Woman With Positive B-HCG and Pai,i or Bleeding
+ ;
Transvaginal Sonogram
I
Intrauterine Gestational Sac Identified?
/ Yes
Gestational Sac Contents Normal?
/ Yes
¢
Diagnose Normal IUP
\ No
Extraovarian Adnexal Complex or Solid Mass?
\
/ No
Suspect Abnormal IUP
Go to Table 1
I
Yes
High Likelihood of Ectopic Pregnancy
\ No
Differential Dx: - Early IUP - Abnormal IUP - Ectopic Pregnancy
Go to Table 2 Serial B-HCG Levels and Sonograms until Diagnosis is Established
Fig 1.
Approach to the sonographic assessment of a woman with pain or bleeding in the first trimester of pregnancy.
When an intrauterine gestational sac is identified, the sac contents should be compared with expected milestones for gestational age, [3-HCG, and other criteria. If the sac contents are appropriate, the patient can be reassured that, despite her symptoms, the prognosis for her pregnancy is quite good. However, if the sac contents are abnormal, in that they fail to meet one or more milestones, pregnancy failure (also referred to as "spontaneous abortion," "fetal demise," and other related terms) should be diagnosed or suspected. The likelihood of a failed pregnancy depends on the nature of the sonographic abnormality (Table 1). Pregnancy failure can be diagnosed with certainty if there is no cardiac activity at a stage in the pregnancy when a heartbeat should always be seen. With transvaginal sonography, this means that a diagnosis of pregnancy failure is made if the sonogram demonstrates no heartbeat when the gestational age is known with certainty to be at least 6.5 weeks, 1,2 or if the sonogram demonstrates no cardiac activity in an embryo whose crown-rump length is ->5 mm. 5,6 A variety of other sonographic findings, such as nonvisualization of a gestational sac when the serum [3-HCG is above 1,000 mIU/mL or nonvisualization of a yolk sac when the mean gestational
sac diameter is at least 8 ram, indicates that pregnancy failure has likely occurred, but the diagnosis is not definitive. 8,9 Furthermore, although the presence of cardiac activity precludes the diagnosis of pregnancy failure at the time of the sonogram, the finding of a slow heartbeat in the early first trimester 7 or a small sac size in relation to a living embryo v is associated with a high likelihood of subsequent pregnancy failure (Table 1). When the sonographic findings are nondefinitive but suggest a high likelihood that the pregnancy has failed, or will soon fail, it is prudent to re-scan the patient 1 to 2 weeks later. If the sonogram demonstrates no intrauterine gestational sac in a woman with bleeding or pain and a positive pregnancy test, the diagnosis of ectopic pregnancy should be considered (Table 2). Other diagnostic possibilities include a very early IUP (<5 weeks) or an abnormal 1UP. If the adnexa appear normal or there is an ovarian cyst but no extra-ovarian adnexal complex or solid mass, the likelihood of ectopic pregnancy is fairly low (approximately 5%). 12 In such cases, the most likely diagnosis is an early 1UP if the [3-HCG is below 500 to 1,000 miU/mL and a failed IUP otherwise. On the other hand, if there is an extra-ovarian adnexal complex or solid mass (Fig 3),
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Fig 2. "Double sac" sign of early pregnancy. Transvaginal sonogram demonstrates an intrauterine fluid collection surrounded by two echogenic rings (inner ring delineated by electronic calipers, outer ring by arrows). The presence of two rings indicates that the fluid collection is a gestational sac.
the likelihood of ectopic pregnancy is very high (>90%) (Table 2). 12 Ectopic pregnancy is a 100% certainty if the adnexal mass contains an embryo or yolk sac (Fig 4). Table 1. Diagnosis of Early Pregnancy Failure by Transvaginal Ultrasonography Diagnose failed pregnancy definitively No cardiac activity is seen and GA is known with certainty to be ->6.5 weeks No cardiac activity is seen in an embryo whose CRL is ->5 mm Suspect failed pregnancy* GA ->5 weeks and no gestational sac is seen GA >-5.5 weeks and no yolk sac is seen GA 6-6,4 weeks and no cardiac activity is identified ~3-HCG ->1000 mlU/mLt and no gestational sac is seen I3-HCG ->10,800 mlU/mLf and no embryo is seen Mean gestational sac diameter ->8 mm and no yolk sac is seen Mean gestational sac diameter ->16 mm and no embryo is seen No cardiac activity is seen in an embryo whose CRL is <5 mm Suspect subsequent pregnancy failure* Slow heart rate at 6 to 7 weeks Small sac size in relation to living embryo *Follow-up scanning in 1 to 2 weeks is recommended, tFirst or third international reference preparation. Values should be halved for second international standard. Abbreviations: GA, gestational age; CRL, crown-rump length; 13-HCG, beta-human chorionic gonadotropin.
The approach to sonographic evaluation of a symptomatic first-trimester patient discussed earlier, and outlined in Figure 1, is based on transvaginal sonography. Although transvaginal sonography is generally sufficient, there are situations in which transabdominal or Doppler sonography may add useful information and help in arriving at a diagnosis. Transabdominal sonography should be performed following any transvaginal scan that does not provide a full view of the uterus and adnexa. In
Table 2. Likelihood of Ectopic Pregnancy Based on Transvaginal Sonographic Findings
Ultrasound Finding Extrauterine embryo with cardiac activity Adnexal fluid collection with either a yolk sac or an apparent embryo without heartbeat Tubal ring Complex or solid adnexat mass without tubal ring, yolk sac, or embryo (excluding masses clearly within an ovary) No significant adnexal abnormalityt
Likelihood of Ectopic Pregnancy* 100% 100% 95%
92% 5%
*Likelihoods apply to women with a positive [3-HCG, pain or bleeding, and no intrauterine gestational sac identified on sonography. tThis includes normal sonograms and scans demonstrating a simple adnexal cyst or an intraovarian lesion. Modified and reprinted with permission. 12
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a prominent ring of color and the spectral waveform demonstrates low-impedance blood flow, the likely diagnosis is ectopic pregnancy. 13q5 It is important to note that, although Doppler is helpful in a small number of cases, there is no need to use Doppler in most cases. For example, Doppler is not helpful if the transvaginal sonogram is entirely normal or if it indicates a high likelihood of ectopic pregnancy.
Role of Ultrasonography in Treatment of Ectopic Pregnancy. In a woman with the definite, or Fig 3. Ectopic pregnancy. Transvaginal sonogram in a woman with a positive ~-HCG and right-sided pelvic pain demonstrates a right-sided complex mass (arrows) and free fluid. The right ovary was seen to be separate from the mass on other images. These findings indicate a very high likelihood (>90%) of ectopic pregnancy.
particular, transabdominal sonography should be done if uterine fibroids limit the transvaginal scan of the pelvis or if the transvaginal scan suggests that there may be a mass high in the pelvis. Advantages of transabdominal sonography in such cases include the ability to use a lower frequency, more highly penetrating transducer, and greater latitude in where to place the transducer. Doppler ultrasonography is occasionally helpful in clarifying the significance of questionable findings on imaging sonography (transvaginal or transabdominal). If sonography demonstrates an area that may or may not represent a pathological mass, the color and spectral Doppler signals from in and around this area may aid in interpretation. If there is
Fig 4. Ectopic pregnancy. Transvaginal demonstrates a right adnexal fluid collection containing a yolk sac (curved arrow) and an embryo (straight arrows) with cardiac activity. These findings are definitive for ectopic pregnancy.
presumed, diagnosis of tubal ectopic pregnancy, the main treatment options include laparoscopic surgery and intramuscular methotrexate injection. 1618 Ultrasonography can help both in selecting the appropriate treatment and in monitoring response to treatment. Treatment with methotrexate is less invasive than surgery, but can only be used in a patient who is stable and who meets a number of sonographic and clinical conditions. In particular, methotrexate therapy is generally believed to be contraindicated if the patient has a complex adnexal mass greater than 3 to 3.5 cm in diameter or a large amount of free intraperitoneal fluid. 17'18 When methotrexate is used, ultrasonography can be used to monitor response to therapy. When this is done, it is important to recognize that the adnexal mass of an ectopic pregnancy often increases in size and vascularity over the first few days after methotrexate injection, before it begins to involute. The mass may take several weeks to resolve completely. 19.20 Ultrasonography also plays a central role in the treatment of cervical ectopic pregnancy (ie, implantation of the gestational sac in the cervix). Cervical ectopics are rare in naturally conceived pregnancies, but occur with greater frequency in pregnancies achieved via in vitro fertilization and other assisted reproductive techniques. 21 Before ultrasonography, it was common for patients with cervical ectopic pregnancies to undergo emergency hysterectomy for life-threatening bleeding, because the diagnosis could not usually be made preoperatively. The diagnosis of cervical ectopic pregnancy was typically made only after pathological examination of the hysterectomy specimen. Ultrasonography permits diagnosis of cervical ectopic pregnancy to be made early in gestation, which in turn has led to minimally invasive, uterus-sparing therapy.=-2s On ultrasonography, a cervical ectopic appears as a round or ovoid sac surrounded by a thick decidual reaction, located within the cervix
EMERGENCY OBSTETRICAL ULTRASONOGRAPHY
(Fig 5A). It is important to distinguish a cervical ectopic from a spontaneous abortion-in-progress. The latter typically appears as an irregularly shaped sac in the cervix or lower uterine segment, with poor decidual reaction (Fig 6). However, sac shape and thickness of decidual reaction are not always sufficient to definitively distinguish between spontaneous abortion-in-progress and cervical ectopic pregnancy. A definitive diagnosis of cervical ectopic pregnancy can be made when there is an intracervical gestational sac that contains an embryo with a heartbeat. If no embryo is seen, the diagnosis is less certain because the intracervical gestational sac could represent an aborting IUE Whenever there is uncertainty about whether an
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intracervical sac represents a cervical ectopic or a spontaneous abortion-in-progress, repeating the scan a day later will generally clarify the situation. If the sac is unchanged in location and appearance, cervical ectopic can be diagnosed with confidence, although a significant change indicates a spontaneous abortion-in-progress. When the diagnosis of cervical ectopic is established, ablation of the ectopic can be performed by guiding a needle into the gestational sac, using a transvaginal transducer with needle guide. If there is an embryo with a heartbeat, the needle is advanced into the embryo (Fig 5B) and potassium chloride is injected until cardiac activity ceases. In the absence of an embryo or heartbeat, potassium chloride or methotrexate is instilled directly into the gestational sac. After injection, the sac progressively decreases in size and the cervix returns to normal over the next few weeks. 23
Second- and Third-Trimester Bleeding
Fig 5. Cervical ectopic pregnancy, (A) Sagittal transvaginal scan demonstrates an intracervical gestational sac containing an embryo (arrows) with cardiac activity. (B) Needle inserted through a guide on the transvaginal transducer ends within the embryo. Potassium chloride was injected, leading to cessation of cardiac activity.
When a patient presents with bleeding in the second or third trimester, the major diagnostic possibilities are placenta previa and placental abruption. Accurate diagnosis of these entities can aid in decisions concerning the timing and route of delivery. Placenta Previa. Placenta previa is defined as a placenta that extends to the internal cervical os. A "complete previa" covers the internal os entirely. A "marginal previa" extends to the edge of, but does not cover, the internal os. A "partial previa" partially covers the internal os. Ultrasonography is the primary modality used for diagnosing placenta previa, but the traditional definitions presented previously are not completely applicable to sonographic evaluation of placental location. It is often difficult to identify the exact location of the internal os, especially when scanning transabdominally, so that it may be impossible to determine the precise relationship between the placenta and the internal os. Furthermore, it has been shown to make little, if any, clinical difference whether the placenta appears sonographically to end exactly at the internal os, 1 to 2 cm short of the os, or 1 to 2 cm over the os. If any of these placental locations is demonstrated on a sonogram shortly before delivery, there is a high likelihood that the patient will have to undergo cesarian delivery because of bleeding characteristic of placenta previa. 26 If any of these placental locations is demon-
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Fig 6. Spontaneous abortion-in-progress. Transvaginal sonogram demonstrates an intracervical gestational sac that is irregular in shape and surrounded by a poor decidual reaction.
strated on a sonogram performed well before delivery, there is a high likelihood that later in pregnancy the placenta will be located far enough away from the internal os to permit vaginal delivery.27,28 In view of the foregoing, a complete previa should be diagnosed by ultrasonography if the cervix (not just the internal os) is completely covered by the placenta (Fig 7), and a marginal previa diagnosed if the placenta extends onto, but not beyond, the cervix (Fig 8). The term "partial previa" does not generally apply to sonographic localization of the placenta because the internal os is usually closed at the time of sonography and, as such, cannot be partially covered.
Sonographic evaluation of placental location can be carried out using a transabdominal, transperineal, or transvaginal approach. In most patients, the presence or absence of a previa can be ascertained by transabdominal sonography, on a sagittal view of the cervix and lower uterine segment through a partially full bladder. An overdistended bladder may lead to the false diagnosis of placenta previa, if the placenta extends to the lower uterine segment and the full bladder pushes the anterior and posterior walls of the lower uterine segment together. If the fetal presenting part obscures the view of the cervix and lower uterine segment, an attempt should be made to manually lift the fetal part 29
Fig 7. Complete placenta previa. Sagittal transabdominal sonogram demonstrates placenta completely covering the cervix.
Fig 8. Marginal placenta previa. Sagittal transabdominal sonogram demonstrates placenta extending to, but not over, the cervix (arrow).
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loss that threatens the life of the fetus or mother. Women with placental abruption typically present with pain and vaginal bleeding. Ultrasonography is the primary imaging modality for diagnosing placental abruption, but diagnosis using ultrasonography is less accurate for this purpose than it is for the diagnosis of placenta previa. Ultrasonography does not detect the separation itself, but can identify a retroplacental or submembranous hematoma (Figs 11 and 12) that may be present with abruption. The hematoma may be hypoechoic or hyperechoic relative to the plaFig 9. Placenta previa. Translabia[ scan demonstrates placenta completely covering the cervix (arrows),
while scanning. If the fetus cannot be dislodged, a translabial (sometimes termed "transperineal") scan3° should be performed. This is done by placing a sector transducer on the labia and scanning sagittally along the axis of the vagina. Translabial sonography generally permits good visualization of the cervix and, therefore, permits diagnosis (Fig 9) or exclusion of placenta previa. However, the cervix is occasionally obscured by rectal gas, and if so, a transvaginal scan should be done. 31,32 With any of these sonographic approaches, the diagnosis of placenta previa should not be made when there is a lower uterine segment contraction. If there is a contraction, the scan should be repeated a few minutes later, after the contraction has resolved. When assessing for previa by ultrasonography, it is important to avoid both false-positive and falsenegative diagnosis, as each can have significant negative consequences. A false-positive diagnosis-diagnosing a previa to be present when the patient does not have a previa--may lead to an unnecessary cesarian delivery. A false-negative diagnosis-interpreting the sonogram as showing no previa when the patient does, in fact, have a previa--may lead to a life-threatening attempt to deliver the fetus vaginally. Use of a sequential strategy (Fig 10) will allow a correct and unequivocal diagnosis or exclusion of placenta previa in virtually all women. Placental Abruption. The placenta normally remains attached to its implantation site in the uterus until the fetus is delivered. Separation of the placenta before this is termed "placental abruption" if it occurs after 20 weeks of gestation. Placental abruption can lead to significant blood
Transabdominal Scan through a Partially Full Bladder
I
If Cervix/Lower Segment is Obscured by Presenting Fetal Part
Attempt to Manually Lift Fetal Part
]
I
If Unable to Lift Fetal Part
TranslabialScan
]
I
If Cervix/Lower Segment is Inadequately Seen
TransvaginalScan
]
Fig 10. Approach to the diagnosis of placenta previa by ultrasonography.
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SONOGRAPHIC FINDINGS REQUIRING URGENT MANAGEMENT
Incompetent Cervix
Fig 11. Placental abruption with retroplacental hematoma. Transabdominal sonogram demonstrates a hypoechoic hamatoma (arrows) under the placenta,
centa, or may have heterogeneous echogenicity with both hypoechoic and hyperechoic areas. There are at least two ways in which a sonogram can appear normal in a patient with an abruption. First, there may be placental separation with no retroplacental or submembranous hematoma. Second, there may be a retroplacental hematoma that is isoechoic with the placenta? 3,34Thus, identification of a retroplacental or submembranous hematoma is diagnostic of abruption, but a normal sonogram does not rule out abruption.
Fig 12. Placental abruption with submembranous hematoma. Transabdominal sonogram demonstrates a hematoma lifting the placental edge (curved arrow) and extending under the membranes (straight arrows),
Incompetent cervix refers to painless dilation of the cervix in the second or early third trimester. In the pre-ultrasonography era, the diagnosis was made on the basis of a history of mid-trimester pregnancy loss. The diagnosis can now be made, or at least suggested, by ultrasonography before a woman experiences a pregnancy loss. The two main sonographic findings associated with incompetent cervix are dilatation of the cervical canal and shortening of the cervix. Either of these findings on its own, or both occurring together, is associated with an elevated risk of preterm delivery. 35-39 Dilatation of the cervical canal begins at the internal os and extends towards the external os. It is identified sonographically by visualizing extension of amniotic fluid into the cervix. The fluid is contained within membranes bulging into the open cervix, but the membranes themselves are not usually visible sonographically. The extent of dilatation can be variable, ranging from minor dilatation of the internal os extending a short distance into the cervix (termed "funneling" or "beaking") (Fig 13A) to dilatation of the full length of the cervix with bulging of membranes through the external os (Fig 14). Cervical length is measured on a sagittal scan plane as the distance between the external os and internal os, if there is no dilatation of the canal (Fig 15). If the canal is dilated, the measurement of cervical length should include only the residual closed portion of the cervical canal (Fig 13B)Y -39 It is often necessary to approximate the location of the internal or external os, as these structures may not be distinctly visible sonographically. The normal cervix measures approximately 3.5 _+ 0.8 cm in length in the third trimester. The risk of spontaneous preterm delivery progressively increases as cervical length decreases. At 24 weeks' gestation, a cervical length of 3 cm carries a 3.8-fold increased risk of spontaneous preterm delivery compared with the risk in a woman whose cervix measures at least 4 cm, whereas a length of 2.6 cm carries a 6.2-fold increased risk. 36 Overall, a cervical length of 2.5 to 3 cm should be considered borderline short, and a length below 2.5 cm should be considered definitely short. Sonographic evaluation of the cervix can be
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Fig 15. Cervical length measurement. Translabial sonogram demonstrates a closed cervical canal, with electronic calipers measuring the length of the cervix.
Fig 13. Incompetent cervix. (A) Translabial sonogram demonstrates partial dilatation of the cervical canal. The canal is dilated internally (arrows). The external portion of the canal is closed. This appearance is termed "beaking" or "funneling." (B) The residual closed portion of the cervix ("x" calipers) and the degree of dilatation of the internal os (" +" calipers) are measured.
Fig 14.
carried out via transabdominal, translabial, or transvaginal sonography. Transabdominal scanning provides the lowest resolution look at the cervix but may be an adequate approach in patients at no apparent risk for cervical incompetence. When examining the cervix transabdominally, the bladder must not be overfilled, as the pressure from a large bladder may eliminate funneling. A very full bladder can also appose the anterior and posterior walls of the lower uterine segment, leading to apparent lengthening of the cervix. In women with clinically suspected cervical incompetence or those in whom the transabdominal scan is not definitive, transla-
Incompetent cervix. Transabdominal sonogram demonstrates dilatation of the full length of the cervical canal.
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Fig 16. incomplete view of the cervix due to shadowing by rectal gas. Translabial sonogram demonstrates obscuration of the external portion of the cervix by shadowing from rectal gas (arrows). Because this image provides only a partial view of the cervix, it is inadequate for measuring cervical length.
bial scanning should be done. 4° If the translabial scan provides an incomplete view of the cervix (eg, if rectal gas shadows out the external portion of the cervix) (Fig 16), transvaginal scanning should be performed (Fig 17), taking care to insert the transducer shallowly and with little pressure. Pressure on the cervix with the transvaginal transducer can lead to the same inaccuracies as can occur with an overfull bladder: elimination of funneling and increase in cervical length. With any of the sonographic approaches, the cervical evaluation should not be done when there is a lower uterine segment contraction. In some women, the appearance of the cervix may change over the course of the sonographic examination. Its length may vary, and the cervical
DOUBILET AND BENSON
Fig 18. Umbilical cord presentation. Transabdominal sonogram demonstrates umbilical cord (arrow) surrounded by amniotic fluid in a dilated cervix.
canal may be dilated at some times and closed at others. The change in appearance may occur spontaneously 41 or can, in some cases, be brought on by exerting manual pressure on the fundus 42 or by having the mother stand upright during the sonogram. 43 With either spontaneous or elicited change in the cervical appearance, the diagnosis of cervical incompetence should be made if the cervix is dilated or short at any time during the sonogram because the risk of preterm labor is related to the greatest degree of dilatation or shortest cervical length. 41-43 Cervical incompetence involves painless dilatation of the cervix, and hence its diagnosis is often made during a scan performed for a routine (ie, nonemergent) indication on an asymptomatic patient. Because the sonographic finding of cervical dilatation or shortening in the second or early third trimester places the patient at risk for preterm delivery, decisions regarding patient management should be made without undue delay. Management options include bed rest or placement of a cerclage (a suture mound the cervix). Umbilical Cord Presentation or Prolapse
Fig 17. Cervical length measured transvaginaliy. Transvaginal sonogram demonstrates the cervix in the near field, with cervical length measured by electronic calipers (arrows).
Sonographic identification of the umbilical cord between the lowermost fetal part and the cervix, within the dilated cervix, or extending through the cervix into the vagina can be accomplished using
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g r a y - s c a l e or D o p p l e r s o n o g r a p h y . 44,45 D o p p l e r is
W h e n u m b i l i c a l c o r d p r e s e n t a t i o n or p r o l a p s e is
n o t n e c e s s a r y i f t h e c o r d is s u r r o u n d e d b y fluid (Fig 18), b u t m a y b e n e e d e d to m a k e t h e d i a g n o s i s i f t h e
seen, a p p r o p r i a t e m a n a g e m e n t s h o u l d b e u n d e r t a k e n to m i n i m i z e t h e r i s k o f c o r d c o m p r e s s i o n a n d
c o r d h a s little or n o fluid a r o u n d it.
fetal h y p o x i a . REFERENCES
1. Timor-Tritsch IE, Farine D, Rosen MG: A close look at early embryonic development with the high-frequency transvaginal transducer. Am J Obstet Gynecol 159:676-681, 1988 2. Goldstein I, Zimmer EA, Tamir A, et al: Evaluation of normal gestational sac growth: Appearance of embryonic heartbeat and embryo body movements using the transvaginal technique. Obstet Gyneco177:885-888, 1991 3. Bree RL, Edwards M, Bohm-Velez M, et al: Transvaginal sonography in the evaluation of normal early pregnancy: Correlation with HCG level. AJR Am J Roentgenol 153:75-79, 1989 4. Levi CS, Lyons EA, Lindsay DJ: Early diagnosis of nonviable pregnancy with endovaginal US. Radiology 167:383385, 1988 5. Levi CS, Lyons EA, Zheng XH, et al: Endovaginal US: Demonstration of cardiac activity in embryos of less than 5.0 mm in crown-rump length. Radiology 176:71-74, 1990 6. Brown DL, Emerson DS, Felker RE, et al: Diagnosis of early embryonic demise by endovaginal sonography. J Ultrasound Med 9:631-636, 1990 7. Doubilet PM, Benson CB: Embryonic heart rate in the early first trimester: what rate is normal? J Ultrasound Med 14:431-434, 1995 8. Mehta TS, Levine D, Beckwith B: Treatment of ectopic pregnancy: Is a human chorionic gonadotropin level of 2000 mlU/ml a reasonable threshold? Radiology 205:569-573, 1997 9. Rowling SE, Coleman BG, Langer JE, et al: First-trimester US parameters of failed pregnancy. Radiology 203:211-217, 1997 10. Nyberg DA, Laing FC, Filly RA, et al: Ultrasonic differentiation of the gestational sac of early pregnancy from the pseudogestational sac of ectopic pregnancy. Radiology 146:755759, 1983 11. Bromley B, Harlow BL, Laboda LA, et al: Small sac size in the first trimester: A predictor of poor fetal outcome. Radiology 178:375-377, 1991 12. Brown DL, Doubilet PM. Transvaginal sonography for diagnosing ectopic pregnancy: positivity criteria and performance characteristics. J Ultrasound Med 13:259-266, 1994 13. Emerson DS, Cartier MS, Altieri LA, et al: Diagnostic efficacy of endovaginal color Doppler flow imaging in an ectopic pregnancy screening program. Radiology 183:413-420, 1992 14. Pellerito JS, Taylor KJW, Qnedens-Case C, et al: Ectopic pregnancy: Evaluation with endovaginal color flow imaging. Radiology 183:407-411, 1992 15. Taylor KJW, Ramos IM, Feyock AL, et al: Ectopic pregnancy: Duplex Doppler evaluation. Radiology 173:93-97, 1989 16. Mascarenhas L, Williamson J, Smith S: The changing face of ectopic pregnancy: Laparoscopic or medical treatment should now replace laparotomy. BMJ 315, 1997 17. Stovall TG, Ling FW: Single-dose methotrexate: An
expanded clinical trial. Am J Obstet Gynecol 168:1759-1765, 1993 18. Yao M, Tulandi T, Falcone T: Treatment of ectopic pregnancy by systemic methotrexate, transvaginal methotrexate, and operative laparoscopy. Int J Fertil 41:470-475, 1996 19. Brown DL, Felker RE, Stovall TG, et al: Serial endovaginal sonography of ectopic pregnancies treated with methotrexate. Obstet Gyneco177:406-409, 1991 20. Atri M, Bret PM, Tulandi T, et al: Ectopic pregnancy: Evolution after treatment with transvaginal methotrexate. Radiology 185:749-753, 1992 21. Ginsburg ES, Frates MC, Rein MS, et al: Early diagnosis and treatment of cervical pregnancy in an in vitro fertilization program. Fertil Steri161:966-969, 1994 22. Timor-Tritsch IE, Monteagudo A, Mandeville EO, et al: Successful management of viable cervical pregnancy by local injection of methotrexate guided by transvaginal ultrasonography. Am J Obstet Gynecol 170:737-739, 1994 23. Frates MC, Benson CB, Doubilet PM, et al: Cervical ectopic pregnancy: Results of conservative treatment. Radiology 191:769-772, 1994 24. Benson CB, Doubilet PM: Strategies for conservative treatment of cervical ectopic pregnancy. Ultrasound Obstet Gynecol 8:371-372, 1996 25. Jurkovic D, Hacket E, Campbell S: Ultrasound diagnosis and conservative management of cervical pregnancy. Ultrasound Obstet Gynecol 8:373-380, 1996 26. Oppenheimer LW, Farine D, Ritchie JWK, et al: What is a low-lying placenta? Am J Obstet Gynecol 165:1036-1038, 1991 27. Gallagher R Fagan CJ, Bedi DG, et al: Potential placenta previa: Definition, frequency, and significance. AJR Am J Roentgenol 149:1013-1015, 1987 28. Zelop CC, Frigoletto Jr FD, Benacerraf BR: Second trimester sonographically diagnosed placenta previa: Prediction of persistent previa at birth. Int J Gynaecol Obstet 44:207-210, 1994 29. Jeffrey RB, Laing FC: Sonography of the low-lying placenta: Value of Trendelenburg and traction scans. AIR Am J Roentgenol 137:547-549, 1981 30. Hertzberg BS, Bowie JD, Carroll BA, et al: Diagnosis of placenta previa during the third trimester: Role of transperineal sonography. A JR Am J Roentgenol 159:83-87, 1992 31. Farine D, Fox HE, Jakobson S, et al: Vaginal ultrasound for diagnosis of placenta previa. Am J Obstet Gynecol 159:566569, 1988 32. Leerentveld RA, Gilberts ECAM, Arnold MJCWJ, et al: Accuracy and safety of transvaginal sonographic placental localization. Obstet Gyneco176:759-762, 1990 33. Mintz MC, Kurtz AB, Arenson R, et al: Abruptio placentae: Apparent thickening of the placenta caused by hyperechoic retroplacental clot. J Ultrasound Med 5:411-413, 1986
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34. Nyberg DA, Cyr DR, Mack LA, et al: Sonographic spectrum of placental abruption. AJR Am J Roentgenol 148:161 1 6 4 , 1987 35. Iams JD, Paraskos J, Landon MB, et ai: Cervical sonography in preterm labor. Obstet Gyneco184:40-46, 1994 36. Iams JD, Goldenberg RL, Meis PJ, et al: The length of the cervix and the risk of spontaneous premature delivery. N Engl J Med 334:567-572, 1996 37. Gomez R, Galasso M, Romero R, et al: Ultrasonographic examination of the uterine cervix is better than cervical digital exam as a predictor of the likelihood of premature delivery in patients with preterm labor and intact membranes. Am J Obstet Gynecol 171:956-964, 1994 38. Riley L, Frigoletto FD, Benacerraf BR: The implications of sonographically identified cervical changes in patients not necessarily at risk for preterm birth. J Ultrasound Med 11:75-79, 1992 39. Berghella V, Kuhlman K, Weiner S, et al: Cervical funneling: Sonographic criteria predictive of preterm delivery. Ultrasound Obstet Gynecol 10:161-166, 1997
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40. Hertzberg BS, Bowie JD, Weber TM, et al: Sonography of the cervix during the third trimester of pregnancy: Value of the transperineal approach. AJR Am J Roentgenol 157:73-76, 1990 41. Hertzberg BS, Kliewer MA, Farrell TA, et al: Spontaneously changing gravid cervix: Clinical implications and prognostic features. Radiology 196:721-724, 1995 42. Guzman ER, Rosenberg JC, Houlihan C, et al: A new method using vaginal ultrasound and transfnndal pressure to evaluate the asymptomatic incompetent cervix. Obstet Gynecol 83:248-252, 1994 43. Wong G, Levine D, Ludmir J: Maternal posmral challenge as a functional test for cervical incompetence. J Ultrasound Med 16:169-175, 1997 44. Hales ED, Westney LS: Sonogaphy of occult cord prolapse. J Clin Ultrasound 12:283-285, 1984 45. Johnson RL, Anderson JC, Irsik RD, et al: Duplex ultrasound diagnosis of umbilical cord prolapse. J Clin Ultrasound 15:282-284, 1987
HE TERM "emergency obstetrical ultrasound' comprises two types of situations involving obstetrical sonography. First are cases where sonography is performed on an emergency basis to evaluate acutely symptomatic pregnant patients, such as those with pelvic pain or vaginal bleeding. When the symptomatic patient is in the first trimester of pregnancy, the role of sonography is to distinguish among a failed (or failing) intrauterine pregnancy, an ectopic pregnancy, and a normal ongoing intrauterine pregnancy. When the symptomatic patient is in the second or third trimesters of pregnancy, the main diagnostic considerations are placenta previa and placental abruption. The second type of emergency obstetrical ultrasound study is one that demonstrates a finding requiring emergent management, such as unexpected cervical dilatation. With either type of emergency sonogram, the ability to make rapid and accurate diagnoses can improve outcome and relieve parental uncertainty and anxiety.
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ULTRASONOGRAPHY OF THE ACUTELY SYMPTOMATIC PREGNANT PATIENT
First-Trimester Bleeding or Pain Role of Ultrasonography in Diagnosis. When a patient presents with a positive pregnancy test and symptoms of vaginal bleeding or pain, she is at elevated risk for having an abnormal pregnancy, including a failed or failing intrauterine pregnancy (IUP) or an ectopic pregnancy. However, bleeding may also occur in an otherwise normal, ongoing IUR Ultrasonography is the primary diagnostic modality for distinguishing among these possibilities. The key to accurate sonographic diagnosis in the symptomatic patient is an understanding and recognition of normal sonographic findings in early pregnancy. Transvaginal sonographic norms for gestational age, serum beta-human chorionic gonadotropin ([~-HCG), and other factors have been established. In a normal pregnancy, a gestational sac is identifiable at 5.0 weeks gestational age 1,2 (using "gestational age" synonymously with "menstrual age"), a yolk sac can be seen within the gestational sac at 5.5 weeks, 3 and cardiac activity is visible at 6.0 weeks. 1,3 A gestational sac can often be seen when the [3-HCG is 500 to 1,000 mIU/mL
and is consistently identifiable when the [3-HCG is > 1,000 mIU/mL. 3 (These values apply to the First and Third International Reference Preparations, and should be halved for the Second International Standard3). When a gestational sac is seen, a yolk sac should be visible within it when the mean gestational sac diameter is ->8 ram, and an embryo should be seen when the mean sac diameter is -> 16 ram. 4 Cardiac activity is always identifiable in a living embryo whose crown-rump length (CRL) is ->5 mm and is most often seen in even smaller embryos. 5,6 The normal heart rate is ->100 bpm before 6.3 weeks and -> 120 bpm at 6.3 to 7 weeks. 7 Most of these norms, or milestones, of early pregnancy should be taken as general guidelines and not as rigid rules, in that a pregnancy that misses a milestone may prove to have a normal outcome. 8,9 For example, although a woman whose sonogram demonstrates an intrauterine gestational sac with mean sac diameter of 8 mm mad no detectable yolk sac will generally prove to have an abnormal pregnancy, there is a chance (albeit small) that she will subsequently be shown to have a normal pregnancy and have a good outcome. 9 When a sonogram is performed in a symptomatic patient in the early first trimester, the diagnosis hinges on the answers to three questions (Fig 1): Does the sonogram demonstrate an intrauterine gestational sac? If so, are the gestational sac contents normal? Are the adnexa normal in appearance? Each of these questions bears further scrutiny. When deciding whether an intrauterine fluid collection represents a gestational sac, care must be taken not to mistake blood or other fluid in the uterine cavity for an IUP. To avoid this error, a gestational sac should be diagnosed only if a fluid collection in the uterus contains an embryo or yolk sac or if it is surrounded by two echogenic rings ("double sac" or "double decidual ring" sign) (Fig 2). l°
From the Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA. Address reprint requests to Peter M. Deubilet, MD, PhD, Department of Radiology, Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115. Copyright © 1998 by WB. Saunders Company 0037-198X/98/3304-000558.00/0
Seminars in Roentgenology, Vol XXXIII, No 4 (October), 1998: pp 339-350
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Woman With Positive B-HCG and Pai,i or Bleeding
+ ;
Transvaginal Sonogram
I
Intrauterine Gestational Sac Identified?
/ Yes
Gestational Sac Contents Normal?
/ Yes
¢
Diagnose Normal IUP
\ No
Extraovarian Adnexal Complex or Solid Mass?
\
/ No
Suspect Abnormal IUP
Go to Table 1
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Differential Dx: - Early IUP - Abnormal IUP - Ectopic Pregnancy
Go to Table 2 Serial B-HCG Levels and Sonograms until Diagnosis is Established
Fig 1.
Approach to the sonographic assessment of a woman with pain or bleeding in the first trimester of pregnancy.
When an intrauterine gestational sac is identified, the sac contents should be compared with expected milestones for gestational age, [3-HCG, and other criteria. If the sac contents are appropriate, the patient can be reassured that, despite her symptoms, the prognosis for her pregnancy is quite good. However, if the sac contents are abnormal, in that they fail to meet one or more milestones, pregnancy failure (also referred to as "spontaneous abortion," "fetal demise," and other related terms) should be diagnosed or suspected. The likelihood of a failed pregnancy depends on the nature of the sonographic abnormality (Table 1). Pregnancy failure can be diagnosed with certainty if there is no cardiac activity at a stage in the pregnancy when a heartbeat should always be seen. With transvaginal sonography, this means that a diagnosis of pregnancy failure is made if the sonogram demonstrates no heartbeat when the gestational age is known with certainty to be at least 6.5 weeks, 1,2 or if the sonogram demonstrates no cardiac activity in an embryo whose crown-rump length is ->5 mm. 5,6 A variety of other sonographic findings, such as nonvisualization of a gestational sac when the serum [3-HCG is above 1,000 mIU/mL or nonvisualization of a yolk sac when the mean gestational
sac diameter is at least 8 ram, indicates that pregnancy failure has likely occurred, but the diagnosis is not definitive. 8,9 Furthermore, although the presence of cardiac activity precludes the diagnosis of pregnancy failure at the time of the sonogram, the finding of a slow heartbeat in the early first trimester 7 or a small sac size in relation to a living embryo v is associated with a high likelihood of subsequent pregnancy failure (Table 1). When the sonographic findings are nondefinitive but suggest a high likelihood that the pregnancy has failed, or will soon fail, it is prudent to re-scan the patient 1 to 2 weeks later. If the sonogram demonstrates no intrauterine gestational sac in a woman with bleeding or pain and a positive pregnancy test, the diagnosis of ectopic pregnancy should be considered (Table 2). Other diagnostic possibilities include a very early IUP (<5 weeks) or an abnormal 1UP. If the adnexa appear normal or there is an ovarian cyst but no extra-ovarian adnexal complex or solid mass, the likelihood of ectopic pregnancy is fairly low (approximately 5%). 12 In such cases, the most likely diagnosis is an early 1UP if the [3-HCG is below 500 to 1,000 miU/mL and a failed IUP otherwise. On the other hand, if there is an extra-ovarian adnexal complex or solid mass (Fig 3),
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Fig 2. "Double sac" sign of early pregnancy. Transvaginal sonogram demonstrates an intrauterine fluid collection surrounded by two echogenic rings (inner ring delineated by electronic calipers, outer ring by arrows). The presence of two rings indicates that the fluid collection is a gestational sac.
the likelihood of ectopic pregnancy is very high (>90%) (Table 2). 12 Ectopic pregnancy is a 100% certainty if the adnexal mass contains an embryo or yolk sac (Fig 4). Table 1. Diagnosis of Early Pregnancy Failure by Transvaginal Ultrasonography Diagnose failed pregnancy definitively No cardiac activity is seen and GA is known with certainty to be ->6.5 weeks No cardiac activity is seen in an embryo whose CRL is ->5 mm Suspect failed pregnancy* GA ->5 weeks and no gestational sac is seen GA >-5.5 weeks and no yolk sac is seen GA 6-6,4 weeks and no cardiac activity is identified ~3-HCG ->1000 mlU/mLt and no gestational sac is seen I3-HCG ->10,800 mlU/mLf and no embryo is seen Mean gestational sac diameter ->8 mm and no yolk sac is seen Mean gestational sac diameter ->16 mm and no embryo is seen No cardiac activity is seen in an embryo whose CRL is <5 mm Suspect subsequent pregnancy failure* Slow heart rate at 6 to 7 weeks Small sac size in relation to living embryo *Follow-up scanning in 1 to 2 weeks is recommended, tFirst or third international reference preparation. Values should be halved for second international standard. Abbreviations: GA, gestational age; CRL, crown-rump length; 13-HCG, beta-human chorionic gonadotropin.
The approach to sonographic evaluation of a symptomatic first-trimester patient discussed earlier, and outlined in Figure 1, is based on transvaginal sonography. Although transvaginal sonography is generally sufficient, there are situations in which transabdominal or Doppler sonography may add useful information and help in arriving at a diagnosis. Transabdominal sonography should be performed following any transvaginal scan that does not provide a full view of the uterus and adnexa. In
Table 2. Likelihood of Ectopic Pregnancy Based on Transvaginal Sonographic Findings
Ultrasound Finding Extrauterine embryo with cardiac activity Adnexal fluid collection with either a yolk sac or an apparent embryo without heartbeat Tubal ring Complex or solid adnexat mass without tubal ring, yolk sac, or embryo (excluding masses clearly within an ovary) No significant adnexal abnormalityt
Likelihood of Ectopic Pregnancy* 100% 100% 95%
92% 5%
*Likelihoods apply to women with a positive [3-HCG, pain or bleeding, and no intrauterine gestational sac identified on sonography. tThis includes normal sonograms and scans demonstrating a simple adnexal cyst or an intraovarian lesion. Modified and reprinted with permission. 12
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a prominent ring of color and the spectral waveform demonstrates low-impedance blood flow, the likely diagnosis is ectopic pregnancy. 13q5 It is important to note that, although Doppler is helpful in a small number of cases, there is no need to use Doppler in most cases. For example, Doppler is not helpful if the transvaginal sonogram is entirely normal or if it indicates a high likelihood of ectopic pregnancy.
Role of Ultrasonography in Treatment of Ectopic Pregnancy. In a woman with the definite, or Fig 3. Ectopic pregnancy. Transvaginal sonogram in a woman with a positive ~-HCG and right-sided pelvic pain demonstrates a right-sided complex mass (arrows) and free fluid. The right ovary was seen to be separate from the mass on other images. These findings indicate a very high likelihood (>90%) of ectopic pregnancy.
particular, transabdominal sonography should be done if uterine fibroids limit the transvaginal scan of the pelvis or if the transvaginal scan suggests that there may be a mass high in the pelvis. Advantages of transabdominal sonography in such cases include the ability to use a lower frequency, more highly penetrating transducer, and greater latitude in where to place the transducer. Doppler ultrasonography is occasionally helpful in clarifying the significance of questionable findings on imaging sonography (transvaginal or transabdominal). If sonography demonstrates an area that may or may not represent a pathological mass, the color and spectral Doppler signals from in and around this area may aid in interpretation. If there is
Fig 4. Ectopic pregnancy. Transvaginal demonstrates a right adnexal fluid collection containing a yolk sac (curved arrow) and an embryo (straight arrows) with cardiac activity. These findings are definitive for ectopic pregnancy.
presumed, diagnosis of tubal ectopic pregnancy, the main treatment options include laparoscopic surgery and intramuscular methotrexate injection. 1618 Ultrasonography can help both in selecting the appropriate treatment and in monitoring response to treatment. Treatment with methotrexate is less invasive than surgery, but can only be used in a patient who is stable and who meets a number of sonographic and clinical conditions. In particular, methotrexate therapy is generally believed to be contraindicated if the patient has a complex adnexal mass greater than 3 to 3.5 cm in diameter or a large amount of free intraperitoneal fluid. 17'18 When methotrexate is used, ultrasonography can be used to monitor response to therapy. When this is done, it is important to recognize that the adnexal mass of an ectopic pregnancy often increases in size and vascularity over the first few days after methotrexate injection, before it begins to involute. The mass may take several weeks to resolve completely. 19.20 Ultrasonography also plays a central role in the treatment of cervical ectopic pregnancy (ie, implantation of the gestational sac in the cervix). Cervical ectopics are rare in naturally conceived pregnancies, but occur with greater frequency in pregnancies achieved via in vitro fertilization and other assisted reproductive techniques. 21 Before ultrasonography, it was common for patients with cervical ectopic pregnancies to undergo emergency hysterectomy for life-threatening bleeding, because the diagnosis could not usually be made preoperatively. The diagnosis of cervical ectopic pregnancy was typically made only after pathological examination of the hysterectomy specimen. Ultrasonography permits diagnosis of cervical ectopic pregnancy to be made early in gestation, which in turn has led to minimally invasive, uterus-sparing therapy.=-2s On ultrasonography, a cervical ectopic appears as a round or ovoid sac surrounded by a thick decidual reaction, located within the cervix
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(Fig 5A). It is important to distinguish a cervical ectopic from a spontaneous abortion-in-progress. The latter typically appears as an irregularly shaped sac in the cervix or lower uterine segment, with poor decidual reaction (Fig 6). However, sac shape and thickness of decidual reaction are not always sufficient to definitively distinguish between spontaneous abortion-in-progress and cervical ectopic pregnancy. A definitive diagnosis of cervical ectopic pregnancy can be made when there is an intracervical gestational sac that contains an embryo with a heartbeat. If no embryo is seen, the diagnosis is less certain because the intracervical gestational sac could represent an aborting IUE Whenever there is uncertainty about whether an
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intracervical sac represents a cervical ectopic or a spontaneous abortion-in-progress, repeating the scan a day later will generally clarify the situation. If the sac is unchanged in location and appearance, cervical ectopic can be diagnosed with confidence, although a significant change indicates a spontaneous abortion-in-progress. When the diagnosis of cervical ectopic is established, ablation of the ectopic can be performed by guiding a needle into the gestational sac, using a transvaginal transducer with needle guide. If there is an embryo with a heartbeat, the needle is advanced into the embryo (Fig 5B) and potassium chloride is injected until cardiac activity ceases. In the absence of an embryo or heartbeat, potassium chloride or methotrexate is instilled directly into the gestational sac. After injection, the sac progressively decreases in size and the cervix returns to normal over the next few weeks. 23
Second- and Third-Trimester Bleeding
Fig 5. Cervical ectopic pregnancy, (A) Sagittal transvaginal scan demonstrates an intracervical gestational sac containing an embryo (arrows) with cardiac activity. (B) Needle inserted through a guide on the transvaginal transducer ends within the embryo. Potassium chloride was injected, leading to cessation of cardiac activity.
When a patient presents with bleeding in the second or third trimester, the major diagnostic possibilities are placenta previa and placental abruption. Accurate diagnosis of these entities can aid in decisions concerning the timing and route of delivery. Placenta Previa. Placenta previa is defined as a placenta that extends to the internal cervical os. A "complete previa" covers the internal os entirely. A "marginal previa" extends to the edge of, but does not cover, the internal os. A "partial previa" partially covers the internal os. Ultrasonography is the primary modality used for diagnosing placenta previa, but the traditional definitions presented previously are not completely applicable to sonographic evaluation of placental location. It is often difficult to identify the exact location of the internal os, especially when scanning transabdominally, so that it may be impossible to determine the precise relationship between the placenta and the internal os. Furthermore, it has been shown to make little, if any, clinical difference whether the placenta appears sonographically to end exactly at the internal os, 1 to 2 cm short of the os, or 1 to 2 cm over the os. If any of these placental locations is demonstrated on a sonogram shortly before delivery, there is a high likelihood that the patient will have to undergo cesarian delivery because of bleeding characteristic of placenta previa. 26 If any of these placental locations is demon-
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Fig 6. Spontaneous abortion-in-progress. Transvaginal sonogram demonstrates an intracervical gestational sac that is irregular in shape and surrounded by a poor decidual reaction.
strated on a sonogram performed well before delivery, there is a high likelihood that later in pregnancy the placenta will be located far enough away from the internal os to permit vaginal delivery.27,28 In view of the foregoing, a complete previa should be diagnosed by ultrasonography if the cervix (not just the internal os) is completely covered by the placenta (Fig 7), and a marginal previa diagnosed if the placenta extends onto, but not beyond, the cervix (Fig 8). The term "partial previa" does not generally apply to sonographic localization of the placenta because the internal os is usually closed at the time of sonography and, as such, cannot be partially covered.
Sonographic evaluation of placental location can be carried out using a transabdominal, transperineal, or transvaginal approach. In most patients, the presence or absence of a previa can be ascertained by transabdominal sonography, on a sagittal view of the cervix and lower uterine segment through a partially full bladder. An overdistended bladder may lead to the false diagnosis of placenta previa, if the placenta extends to the lower uterine segment and the full bladder pushes the anterior and posterior walls of the lower uterine segment together. If the fetal presenting part obscures the view of the cervix and lower uterine segment, an attempt should be made to manually lift the fetal part 29
Fig 7. Complete placenta previa. Sagittal transabdominal sonogram demonstrates placenta completely covering the cervix.
Fig 8. Marginal placenta previa. Sagittal transabdominal sonogram demonstrates placenta extending to, but not over, the cervix (arrow).
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loss that threatens the life of the fetus or mother. Women with placental abruption typically present with pain and vaginal bleeding. Ultrasonography is the primary imaging modality for diagnosing placental abruption, but diagnosis using ultrasonography is less accurate for this purpose than it is for the diagnosis of placenta previa. Ultrasonography does not detect the separation itself, but can identify a retroplacental or submembranous hematoma (Figs 11 and 12) that may be present with abruption. The hematoma may be hypoechoic or hyperechoic relative to the plaFig 9. Placenta previa. Translabia[ scan demonstrates placenta completely covering the cervix (arrows),
while scanning. If the fetus cannot be dislodged, a translabial (sometimes termed "transperineal") scan3° should be performed. This is done by placing a sector transducer on the labia and scanning sagittally along the axis of the vagina. Translabial sonography generally permits good visualization of the cervix and, therefore, permits diagnosis (Fig 9) or exclusion of placenta previa. However, the cervix is occasionally obscured by rectal gas, and if so, a transvaginal scan should be done. 31,32 With any of these sonographic approaches, the diagnosis of placenta previa should not be made when there is a lower uterine segment contraction. If there is a contraction, the scan should be repeated a few minutes later, after the contraction has resolved. When assessing for previa by ultrasonography, it is important to avoid both false-positive and falsenegative diagnosis, as each can have significant negative consequences. A false-positive diagnosis-diagnosing a previa to be present when the patient does not have a previa--may lead to an unnecessary cesarian delivery. A false-negative diagnosis-interpreting the sonogram as showing no previa when the patient does, in fact, have a previa--may lead to a life-threatening attempt to deliver the fetus vaginally. Use of a sequential strategy (Fig 10) will allow a correct and unequivocal diagnosis or exclusion of placenta previa in virtually all women. Placental Abruption. The placenta normally remains attached to its implantation site in the uterus until the fetus is delivered. Separation of the placenta before this is termed "placental abruption" if it occurs after 20 weeks of gestation. Placental abruption can lead to significant blood
Transabdominal Scan through a Partially Full Bladder
I
If Cervix/Lower Segment is Obscured by Presenting Fetal Part
Attempt to Manually Lift Fetal Part
]
I
If Unable to Lift Fetal Part
TranslabialScan
]
I
If Cervix/Lower Segment is Inadequately Seen
TransvaginalScan
]
Fig 10. Approach to the diagnosis of placenta previa by ultrasonography.
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SONOGRAPHIC FINDINGS REQUIRING URGENT MANAGEMENT
Incompetent Cervix
Fig 11. Placental abruption with retroplacental hematoma. Transabdominal sonogram demonstrates a hypoechoic hamatoma (arrows) under the placenta,
centa, or may have heterogeneous echogenicity with both hypoechoic and hyperechoic areas. There are at least two ways in which a sonogram can appear normal in a patient with an abruption. First, there may be placental separation with no retroplacental or submembranous hematoma. Second, there may be a retroplacental hematoma that is isoechoic with the placenta? 3,34Thus, identification of a retroplacental or submembranous hematoma is diagnostic of abruption, but a normal sonogram does not rule out abruption.
Fig 12. Placental abruption with submembranous hematoma. Transabdominal sonogram demonstrates a hematoma lifting the placental edge (curved arrow) and extending under the membranes (straight arrows),
Incompetent cervix refers to painless dilation of the cervix in the second or early third trimester. In the pre-ultrasonography era, the diagnosis was made on the basis of a history of mid-trimester pregnancy loss. The diagnosis can now be made, or at least suggested, by ultrasonography before a woman experiences a pregnancy loss. The two main sonographic findings associated with incompetent cervix are dilatation of the cervical canal and shortening of the cervix. Either of these findings on its own, or both occurring together, is associated with an elevated risk of preterm delivery. 35-39 Dilatation of the cervical canal begins at the internal os and extends towards the external os. It is identified sonographically by visualizing extension of amniotic fluid into the cervix. The fluid is contained within membranes bulging into the open cervix, but the membranes themselves are not usually visible sonographically. The extent of dilatation can be variable, ranging from minor dilatation of the internal os extending a short distance into the cervix (termed "funneling" or "beaking") (Fig 13A) to dilatation of the full length of the cervix with bulging of membranes through the external os (Fig 14). Cervical length is measured on a sagittal scan plane as the distance between the external os and internal os, if there is no dilatation of the canal (Fig 15). If the canal is dilated, the measurement of cervical length should include only the residual closed portion of the cervical canal (Fig 13B)Y -39 It is often necessary to approximate the location of the internal or external os, as these structures may not be distinctly visible sonographically. The normal cervix measures approximately 3.5 _+ 0.8 cm in length in the third trimester. The risk of spontaneous preterm delivery progressively increases as cervical length decreases. At 24 weeks' gestation, a cervical length of 3 cm carries a 3.8-fold increased risk of spontaneous preterm delivery compared with the risk in a woman whose cervix measures at least 4 cm, whereas a length of 2.6 cm carries a 6.2-fold increased risk. 36 Overall, a cervical length of 2.5 to 3 cm should be considered borderline short, and a length below 2.5 cm should be considered definitely short. Sonographic evaluation of the cervix can be
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Fig 15. Cervical length measurement. Translabial sonogram demonstrates a closed cervical canal, with electronic calipers measuring the length of the cervix.
Fig 13. Incompetent cervix. (A) Translabial sonogram demonstrates partial dilatation of the cervical canal. The canal is dilated internally (arrows). The external portion of the canal is closed. This appearance is termed "beaking" or "funneling." (B) The residual closed portion of the cervix ("x" calipers) and the degree of dilatation of the internal os (" +" calipers) are measured.
Fig 14.
carried out via transabdominal, translabial, or transvaginal sonography. Transabdominal scanning provides the lowest resolution look at the cervix but may be an adequate approach in patients at no apparent risk for cervical incompetence. When examining the cervix transabdominally, the bladder must not be overfilled, as the pressure from a large bladder may eliminate funneling. A very full bladder can also appose the anterior and posterior walls of the lower uterine segment, leading to apparent lengthening of the cervix. In women with clinically suspected cervical incompetence or those in whom the transabdominal scan is not definitive, transla-
Incompetent cervix. Transabdominal sonogram demonstrates dilatation of the full length of the cervical canal.
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Fig 16. incomplete view of the cervix due to shadowing by rectal gas. Translabial sonogram demonstrates obscuration of the external portion of the cervix by shadowing from rectal gas (arrows). Because this image provides only a partial view of the cervix, it is inadequate for measuring cervical length.
bial scanning should be done. 4° If the translabial scan provides an incomplete view of the cervix (eg, if rectal gas shadows out the external portion of the cervix) (Fig 16), transvaginal scanning should be performed (Fig 17), taking care to insert the transducer shallowly and with little pressure. Pressure on the cervix with the transvaginal transducer can lead to the same inaccuracies as can occur with an overfull bladder: elimination of funneling and increase in cervical length. With any of the sonographic approaches, the cervical evaluation should not be done when there is a lower uterine segment contraction. In some women, the appearance of the cervix may change over the course of the sonographic examination. Its length may vary, and the cervical
DOUBILET AND BENSON
Fig 18. Umbilical cord presentation. Transabdominal sonogram demonstrates umbilical cord (arrow) surrounded by amniotic fluid in a dilated cervix.
canal may be dilated at some times and closed at others. The change in appearance may occur spontaneously 41 or can, in some cases, be brought on by exerting manual pressure on the fundus 42 or by having the mother stand upright during the sonogram. 43 With either spontaneous or elicited change in the cervical appearance, the diagnosis of cervical incompetence should be made if the cervix is dilated or short at any time during the sonogram because the risk of preterm labor is related to the greatest degree of dilatation or shortest cervical length. 41-43 Cervical incompetence involves painless dilatation of the cervix, and hence its diagnosis is often made during a scan performed for a routine (ie, nonemergent) indication on an asymptomatic patient. Because the sonographic finding of cervical dilatation or shortening in the second or early third trimester places the patient at risk for preterm delivery, decisions regarding patient management should be made without undue delay. Management options include bed rest or placement of a cerclage (a suture mound the cervix). Umbilical Cord Presentation or Prolapse
Fig 17. Cervical length measured transvaginaliy. Transvaginal sonogram demonstrates the cervix in the near field, with cervical length measured by electronic calipers (arrows).
Sonographic identification of the umbilical cord between the lowermost fetal part and the cervix, within the dilated cervix, or extending through the cervix into the vagina can be accomplished using
EMERGENCY OBSTETRICAL ULTRASONOGRAPHY
349
g r a y - s c a l e or D o p p l e r s o n o g r a p h y . 44,45 D o p p l e r is
W h e n u m b i l i c a l c o r d p r e s e n t a t i o n or p r o l a p s e is
n o t n e c e s s a r y i f t h e c o r d is s u r r o u n d e d b y fluid (Fig 18), b u t m a y b e n e e d e d to m a k e t h e d i a g n o s i s i f t h e
seen, a p p r o p r i a t e m a n a g e m e n t s h o u l d b e u n d e r t a k e n to m i n i m i z e t h e r i s k o f c o r d c o m p r e s s i o n a n d
c o r d h a s little or n o fluid a r o u n d it.
fetal h y p o x i a . REFERENCES
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