- Email: [email protected]
The use of obstetrical ultrasound in the obese gravida
SE
M I N A R S I N
P
E R I N A T O L O G Y
37 (2013) 345–347
Available online at www.sciencedirect.com
www.elsevier.com/locate/semperi
The use of obstetrical ultrasound in the obese gravida Beryl Benacerraf, MDa,b,c,n a
Department of Radiology, Brigham and Women's Hospital, Boston, MA Department of OB GYN, Brigham and Women's Hospital, Boston, MA c Department OBGYN, Massachusetts General Hospital, Harvard Medical School, Boston, MA b
ART IC LE INFO
abstra ct Obesity is an epidemic in the United States, especially among the pregnant population.
Keywords:
Obesity is responsible for an increase in fetal anomalies and adverse outcome of both
Ultrasound
mother and fetus. Due to difficulty in penetrating to the depth of the uterus, the ultrasound
Obesity
image in obese patients is inadequate, fuzzy, and high in artifacts. Hence, obese patients
Fetal anomalies
often require multiple scans as well as special scanning techniques just to get borderline
Ultrasound technique
image quality. These techniques and the data regarding quality and frequency of scans for the obese pregnant population are discussed in this paper. & 2013 Elsevier Inc. All rights reserved.
Obesity is a worldwide epidemic, but particularly prevalent in the United States, where more than 60% of the population is considered overweight.1 Adipose tissue makes ultrasound imaging especially challenging, placing fetuses of obese patients at a great disadvantage.1,2 Performing a fetal ultrasound in an obese gravida results in a technically inferior examination compared to the same ultrasound examination done on patients of normal weight. The ultrasound beam is increasingly degraded as it penetrates deeper to reach the gravid uterus.1 The quality of the image produced is inversely proportional to the distance that the beam must travel and in obese patients, the ultrasound beam is absorbed and dispersed, resulting in an inadequate evaluation of fetal anatomy. Ultrasound technology has made great strides in improving image quality using compound imaging, speckle-reduction filters, pre- and post-processing filters, and tissue harmonic imaging.3,4 The ultrasound image of the fetus in obese patients is still inadequate however, resulting in fuzzy image, riddled with noise, backscatter, and artifacts.1 Despite these technical enhancements in ultrasound technology, ultrasound imaging of the obese gravidas remains an increasingly difficult problem, not only due to the technical imaging
n
difficulties but also because these patients are at increased risk for adverse outcome. There is a growing body of evidence showing that obese patients are at an increased risk for adverse pregnancy outcome both from a maternal and fetal point of view. Fetal structural malformations are more common in obese patients and yet the ultrasound examinations are often inadequate, forcing the practitioners to repeat these examinations later in
Table 1 – Risks incurred by obese gravidas Maternal risks
Fetal risks
Maternal death or severe morbidity Cardiac disease Recurrent spontaneous abortions Pre-eclampsia Gestational diabetes Thromboembolism Cesarean-section wound infection Postpartum hemorrhage
Stillbirth and neonatal death Congenital anomalies Prematurity Macrosomia
Correspondence address: One Brookline Place, Brookline, MA 02445. E-mail address: [email protected]
0146-0005/13/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1053/j.semperi.2013.06.012
346
SE
M I N A R S I N
P
Table 2 – The risk of fetal anomalies in obese gravidas. Anomaly
OR (95% CI)
p Value
Neural tube defect Cardiac anomalies Anal atresia Limb reduction
1.87 1.30 1.48 1.34
0.001 0.001 0.006 0.03
(1.62–2.15) (1.12–1.51) (1.12–1.97) (1.03–1.73)
37 (2013) 345–347
E R I N A T O L O G Y
Adapted from Stothard et al.6
Table 3 – The effect of obesity on the adequacy of fetal anatomy scan.
Adequate scan (%)
Normal
Overweight, BMI 25–29
Class 1, BMI 30–34
Class 2, BMI 35–39
Class 3, BMI ≥ 40
72
68
57
41
30
Adapted from Dashe et al.7
pregnancy for better diagnostic quality.5 Table 1 shows the types of adverse outcomes for which obese gravidas are at increased risk compared to the general population. Both the mother and the fetus are at high risk for these complications making the management of such obese gravidas challenging. Many of these patients require multiple ultrasound examinations to manage their prenatal care. Stothard et al.6 showed that the risk of certain fetal anomalies is significantly higher in obese patients compared to normal population, especially neural tube defects, cardiac anomalies, anal atresia, and limb-reduction abnormalities (Table 2). Yet in more than 50% of obese women the fetal anatomic survey cannot be completed at the time of the first ultrasound examination. Dashe et al.7 studied the effect of obesity on routine second trimester ultrasound examinations at 18–24 weeks, using a cohort of 10,112 patients, 34% of whom were overweight and 26% of whom were obese. Ten anatomic views were evaluated for adequacy: cerebral ventricles, posterior fossa, midline face, four chambers, spine, ventral wall, cord vessels, stomach, kidneys, and bladder. Table 3 and Table 4 shows the distribution of successful scans by obesity class, showing a steady degradation in scan quality with increasing body mass index (BMI).7 Hendler et al.8 showed that the rate of poor visualization was worse in the obese group for both the fetal heart (37% vs. 19%) and spine (43% vs. 29%), which correlated linearly with the degree of obesity. When the ultrasound examination was repeated at 21 weeks, there was improvement in the visualization of cardiac anatomy in all classes of obesity, although the heart could still not be adequately assessed in up to 20% of the obese population despite multiple ultrasound examinations.8 The importance of adequate views of the fetal heart in obese gravidas is paramount due to the higher incidence of heart defects in these fetuses.9 Uhden et al.10 showed that the prevalence of heart defects was higher (relative risk ¼ 2.04) in overweight and obese women (BMI 425) compared to those of normal weight. And yet, the quality of insufficient ultrasound images increased from 6.4% in normal weight patients to 17.4% in obese women10.
The FaSTER trial was designed to identify fetuses with Down syndrome as well as other abnormalities, but one important result from this trial relates to the detection of anomalies in obese gravidas.11 The cardiac anomalies were identified at a higher rate in women with BMI o25 with a significantly lower false-positive rate in comparison to obese women. In a logistic regression model, the presence of maternal obesity decreased the likelihood that common fetal anomalies would be detected sonographically (adjusted OR 0.7; 95% CI 0.6–0.9; p ¼ 0.001).11 Table 5 lists the techniques that can be helpful in the sonographic imaging of obese patients. These methods attempt to diminish the distance between the transducer and the uterus, which is one of the sources of the problem. The practitioner can lift the panniculus, thus scanning underneath it, just over the pubic bone, or using the umbilicus as an acoustic window. One can even perform the ultrasound above the panniculus in the region of the mid-abdomen, pushing the panniculus down thus making the distance between the skin surface and the fetus shorter. If the patient's bladder is filled, the fundus of the uterus will be raised to a more cephalad level where the adipose tissue in the anterior abdominal wall is more narrow improving the image in some patients.1 Other techniques to improve the technical quality of the images that can be done on obese gravidas include scanning them in the sitting position, placing the transducer cephalad to the thickest part of the maternal abdomen with the ultrasound beam penetrating the uterus at the fundus. The transvaginal approach is also very helpful as the images are produced with a higherfrequency transducer that can be placed closer to the fetal anatomy than when using the transabdominal method. Once the fetus is beyond the first trimester, it may be necessary to manipulate the fetal position by pressing on the maternal abdomen with the practitioner's free hand to move the fetus into different orientations while scanning transvaginally.12 Lastly, the Sims position places the patient on her side rotating ventrally and allows the practitioner to approach
Table 4 – Adequacy of genetic sonogram 5690 patient based on degree of obesity.
Survey complete at first attempt (%) Gestational age at completion (weeks) Adapted from Tsai et al.9
Normal
Overweight, BMI 25–29
Class 1, BMI 30–34
Class 2, BMI 35–39
Class 3, BMI ≥ 40
63 19.7
62 19.7
58 20.0
51 20.1
41 20.5
S
E M I N A R S I N
P
E R I N A T O L O G Y
Table 5 – Ways to improve quality of obstetrical ultrasound in obese gravidas. a. Improve the signal-to-noise ratio. i. Compound imaging, speckle-reduction filters, pre- and postprocessing, and tissue harmonics.
b. c. d. e. f.
Full maternal bladder. Use umbilicus as acoustic window. Sitting up and image above panniculus. Sims position and image from flank or groin. Transvaginal scan with manipulation of fetus externally.
the fetus through the mother's flank or groin where the adipose tissue is thinner.12 In conclusion, obesity is an epidemic and results in an increased risk for fetal anomalies and adverse outcome of both mother and fetus. Obese patients present a technical problem and therefore adequate imaging often requires repeat examinations just to get borderline image quality. Multiple scans as well as special techniques are often required to improve the sonographic image quality of in these patients.
re fe r en ces
1. Paladini D. Sonography in the obese and overweight pregnant women: clinical, medicolegal and technical issues. Ultrasound Obstet Gynecol. 2009;33:720–729.
37 (2013) 345–347
347
2. Dashe JS, McIntire D, Twickler DM. Maternal obesity limits the ultrasound evaluation of fetal anatomy. J Ultrasound Med. 2009;28:1025–1030. 3. Tranquart F, Grenier N, Eder V, Pourcelot L. Clinical use of ultrasound tissue harmonic imaging. Ultrasound Med Biol. 1999;25:889–894. 4. Paladini D, Vassallo M, Tartaglione A, Lapadula C, Martinelli P. The role of tissue harmonic imaging in fetal echocardiography. Ultrasound Obstet Gynecol. 2004;23:159–164. 5. Hendler I, Blackwell SC, Bujold E, et al. Suboptimal secondtrimester ultrasonographic visualization of the fetal heart in obese women: should we repeat the examination? J Ultrasound Med. 2005;24:1205–1209. 6. Stothard KJ, Tennant PWG, Bell R, Rankin J. Maternal Overweight and obesity and the risk of congenital anomalies. A systematic review and meta-analysis. J Am Med Assoc. 2009; 301:636–650. 7. Dashe JS, McIntire DD, Twickler DM. Maternal obesity limits the ultrasound evaluation of fetal anatomy. J Ultrasound Med. 2009;28:1025–1030. 8. Hendler I, Blackwell SC, Bujold E, et al. The impact of maternal obesity on midtrimester sonographic visualization of fetal cardiac and craniospinal structures. Int J Obes Relat Metab Disord. 2004;28:1607–1611. 9. Tsai LJ, Ho M, Pressman EK, Thornburg L. Ultrasound screening for fetal aneuploidy using soft markers in the overweight and obese gravida. Prenatal Diagn. 2010;30(9):821–826. 10. Uhden M, Knippel AJ, Stressig R, et al. Impact of maternal obesity and maternal overweight on the detection rate of fetal heart defects and the image quality of prenatal echocardiography. Ultraschall Med. 2011;32(2):E108–E114. 11. Aagaard-Tillery KM, Flint Porter T, Malone FD, et al. Influence of maternal BMI on genetic sonography in the FaSTER trial. Prenat Diagn. 2010;30:14–22. 12. Benacerraf BR. A technical tip on scanning obese gravidas. Ultrasound Obstet Gynecol. 2010;35:615–616.
M I N A R S I N
P
E R I N A T O L O G Y
37 (2013) 345–347
Available online at www.sciencedirect.com
www.elsevier.com/locate/semperi
The use of obstetrical ultrasound in the obese gravida Beryl Benacerraf, MDa,b,c,n a
Department of Radiology, Brigham and Women's Hospital, Boston, MA Department of OB GYN, Brigham and Women's Hospital, Boston, MA c Department OBGYN, Massachusetts General Hospital, Harvard Medical School, Boston, MA b
ART IC LE INFO
abstra ct Obesity is an epidemic in the United States, especially among the pregnant population.
Keywords:
Obesity is responsible for an increase in fetal anomalies and adverse outcome of both
Ultrasound
mother and fetus. Due to difficulty in penetrating to the depth of the uterus, the ultrasound
Obesity
image in obese patients is inadequate, fuzzy, and high in artifacts. Hence, obese patients
Fetal anomalies
often require multiple scans as well as special scanning techniques just to get borderline
Ultrasound technique
image quality. These techniques and the data regarding quality and frequency of scans for the obese pregnant population are discussed in this paper. & 2013 Elsevier Inc. All rights reserved.
Obesity is a worldwide epidemic, but particularly prevalent in the United States, where more than 60% of the population is considered overweight.1 Adipose tissue makes ultrasound imaging especially challenging, placing fetuses of obese patients at a great disadvantage.1,2 Performing a fetal ultrasound in an obese gravida results in a technically inferior examination compared to the same ultrasound examination done on patients of normal weight. The ultrasound beam is increasingly degraded as it penetrates deeper to reach the gravid uterus.1 The quality of the image produced is inversely proportional to the distance that the beam must travel and in obese patients, the ultrasound beam is absorbed and dispersed, resulting in an inadequate evaluation of fetal anatomy. Ultrasound technology has made great strides in improving image quality using compound imaging, speckle-reduction filters, pre- and post-processing filters, and tissue harmonic imaging.3,4 The ultrasound image of the fetus in obese patients is still inadequate however, resulting in fuzzy image, riddled with noise, backscatter, and artifacts.1 Despite these technical enhancements in ultrasound technology, ultrasound imaging of the obese gravidas remains an increasingly difficult problem, not only due to the technical imaging
n
difficulties but also because these patients are at increased risk for adverse outcome. There is a growing body of evidence showing that obese patients are at an increased risk for adverse pregnancy outcome both from a maternal and fetal point of view. Fetal structural malformations are more common in obese patients and yet the ultrasound examinations are often inadequate, forcing the practitioners to repeat these examinations later in
Table 1 – Risks incurred by obese gravidas Maternal risks
Fetal risks
Maternal death or severe morbidity Cardiac disease Recurrent spontaneous abortions Pre-eclampsia Gestational diabetes Thromboembolism Cesarean-section wound infection Postpartum hemorrhage
Stillbirth and neonatal death Congenital anomalies Prematurity Macrosomia
Correspondence address: One Brookline Place, Brookline, MA 02445. E-mail address: [email protected]
0146-0005/13/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1053/j.semperi.2013.06.012
346
SE
M I N A R S I N
P
Table 2 – The risk of fetal anomalies in obese gravidas. Anomaly
OR (95% CI)
p Value
Neural tube defect Cardiac anomalies Anal atresia Limb reduction
1.87 1.30 1.48 1.34
0.001 0.001 0.006 0.03
(1.62–2.15) (1.12–1.51) (1.12–1.97) (1.03–1.73)
37 (2013) 345–347
E R I N A T O L O G Y
Adapted from Stothard et al.6
Table 3 – The effect of obesity on the adequacy of fetal anatomy scan.
Adequate scan (%)
Normal
Overweight, BMI 25–29
Class 1, BMI 30–34
Class 2, BMI 35–39
Class 3, BMI ≥ 40
72
68
57
41
30
Adapted from Dashe et al.7
pregnancy for better diagnostic quality.5 Table 1 shows the types of adverse outcomes for which obese gravidas are at increased risk compared to the general population. Both the mother and the fetus are at high risk for these complications making the management of such obese gravidas challenging. Many of these patients require multiple ultrasound examinations to manage their prenatal care. Stothard et al.6 showed that the risk of certain fetal anomalies is significantly higher in obese patients compared to normal population, especially neural tube defects, cardiac anomalies, anal atresia, and limb-reduction abnormalities (Table 2). Yet in more than 50% of obese women the fetal anatomic survey cannot be completed at the time of the first ultrasound examination. Dashe et al.7 studied the effect of obesity on routine second trimester ultrasound examinations at 18–24 weeks, using a cohort of 10,112 patients, 34% of whom were overweight and 26% of whom were obese. Ten anatomic views were evaluated for adequacy: cerebral ventricles, posterior fossa, midline face, four chambers, spine, ventral wall, cord vessels, stomach, kidneys, and bladder. Table 3 and Table 4 shows the distribution of successful scans by obesity class, showing a steady degradation in scan quality with increasing body mass index (BMI).7 Hendler et al.8 showed that the rate of poor visualization was worse in the obese group for both the fetal heart (37% vs. 19%) and spine (43% vs. 29%), which correlated linearly with the degree of obesity. When the ultrasound examination was repeated at 21 weeks, there was improvement in the visualization of cardiac anatomy in all classes of obesity, although the heart could still not be adequately assessed in up to 20% of the obese population despite multiple ultrasound examinations.8 The importance of adequate views of the fetal heart in obese gravidas is paramount due to the higher incidence of heart defects in these fetuses.9 Uhden et al.10 showed that the prevalence of heart defects was higher (relative risk ¼ 2.04) in overweight and obese women (BMI 425) compared to those of normal weight. And yet, the quality of insufficient ultrasound images increased from 6.4% in normal weight patients to 17.4% in obese women10.
The FaSTER trial was designed to identify fetuses with Down syndrome as well as other abnormalities, but one important result from this trial relates to the detection of anomalies in obese gravidas.11 The cardiac anomalies were identified at a higher rate in women with BMI o25 with a significantly lower false-positive rate in comparison to obese women. In a logistic regression model, the presence of maternal obesity decreased the likelihood that common fetal anomalies would be detected sonographically (adjusted OR 0.7; 95% CI 0.6–0.9; p ¼ 0.001).11 Table 5 lists the techniques that can be helpful in the sonographic imaging of obese patients. These methods attempt to diminish the distance between the transducer and the uterus, which is one of the sources of the problem. The practitioner can lift the panniculus, thus scanning underneath it, just over the pubic bone, or using the umbilicus as an acoustic window. One can even perform the ultrasound above the panniculus in the region of the mid-abdomen, pushing the panniculus down thus making the distance between the skin surface and the fetus shorter. If the patient's bladder is filled, the fundus of the uterus will be raised to a more cephalad level where the adipose tissue in the anterior abdominal wall is more narrow improving the image in some patients.1 Other techniques to improve the technical quality of the images that can be done on obese gravidas include scanning them in the sitting position, placing the transducer cephalad to the thickest part of the maternal abdomen with the ultrasound beam penetrating the uterus at the fundus. The transvaginal approach is also very helpful as the images are produced with a higherfrequency transducer that can be placed closer to the fetal anatomy than when using the transabdominal method. Once the fetus is beyond the first trimester, it may be necessary to manipulate the fetal position by pressing on the maternal abdomen with the practitioner's free hand to move the fetus into different orientations while scanning transvaginally.12 Lastly, the Sims position places the patient on her side rotating ventrally and allows the practitioner to approach
Table 4 – Adequacy of genetic sonogram 5690 patient based on degree of obesity.
Survey complete at first attempt (%) Gestational age at completion (weeks) Adapted from Tsai et al.9
Normal
Overweight, BMI 25–29
Class 1, BMI 30–34
Class 2, BMI 35–39
Class 3, BMI ≥ 40
63 19.7
62 19.7
58 20.0
51 20.1
41 20.5
S
E M I N A R S I N
P
E R I N A T O L O G Y
Table 5 – Ways to improve quality of obstetrical ultrasound in obese gravidas. a. Improve the signal-to-noise ratio. i. Compound imaging, speckle-reduction filters, pre- and postprocessing, and tissue harmonics.
b. c. d. e. f.
Full maternal bladder. Use umbilicus as acoustic window. Sitting up and image above panniculus. Sims position and image from flank or groin. Transvaginal scan with manipulation of fetus externally.
the fetus through the mother's flank or groin where the adipose tissue is thinner.12 In conclusion, obesity is an epidemic and results in an increased risk for fetal anomalies and adverse outcome of both mother and fetus. Obese patients present a technical problem and therefore adequate imaging often requires repeat examinations just to get borderline image quality. Multiple scans as well as special techniques are often required to improve the sonographic image quality of in these patients.
re fe r en ces
1. Paladini D. Sonography in the obese and overweight pregnant women: clinical, medicolegal and technical issues. Ultrasound Obstet Gynecol. 2009;33:720–729.
37 (2013) 345–347
347
2. Dashe JS, McIntire D, Twickler DM. Maternal obesity limits the ultrasound evaluation of fetal anatomy. J Ultrasound Med. 2009;28:1025–1030. 3. Tranquart F, Grenier N, Eder V, Pourcelot L. Clinical use of ultrasound tissue harmonic imaging. Ultrasound Med Biol. 1999;25:889–894. 4. Paladini D, Vassallo M, Tartaglione A, Lapadula C, Martinelli P. The role of tissue harmonic imaging in fetal echocardiography. Ultrasound Obstet Gynecol. 2004;23:159–164. 5. Hendler I, Blackwell SC, Bujold E, et al. Suboptimal secondtrimester ultrasonographic visualization of the fetal heart in obese women: should we repeat the examination? J Ultrasound Med. 2005;24:1205–1209. 6. Stothard KJ, Tennant PWG, Bell R, Rankin J. Maternal Overweight and obesity and the risk of congenital anomalies. A systematic review and meta-analysis. J Am Med Assoc. 2009; 301:636–650. 7. Dashe JS, McIntire DD, Twickler DM. Maternal obesity limits the ultrasound evaluation of fetal anatomy. J Ultrasound Med. 2009;28:1025–1030. 8. Hendler I, Blackwell SC, Bujold E, et al. The impact of maternal obesity on midtrimester sonographic visualization of fetal cardiac and craniospinal structures. Int J Obes Relat Metab Disord. 2004;28:1607–1611. 9. Tsai LJ, Ho M, Pressman EK, Thornburg L. Ultrasound screening for fetal aneuploidy using soft markers in the overweight and obese gravida. Prenatal Diagn. 2010;30(9):821–826. 10. Uhden M, Knippel AJ, Stressig R, et al. Impact of maternal obesity and maternal overweight on the detection rate of fetal heart defects and the image quality of prenatal echocardiography. Ultraschall Med. 2011;32(2):E108–E114. 11. Aagaard-Tillery KM, Flint Porter T, Malone FD, et al. Influence of maternal BMI on genetic sonography in the FaSTER trial. Prenat Diagn. 2010;30:14–22. 12. Benacerraf BR. A technical tip on scanning obese gravidas. Ultrasound Obstet Gynecol. 2010;35:615–616.