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Ante- and intrapartum diagnosis of vasa praevia in singleton pregnancies by colour coded Doppler sonography
European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19–25
Ante- and intrapartum diagnosis of vasa praevia in singleton pregnancies by colour coded Doppler sonography Ahmet Alexander Baschat*, Ulrich Gembruch ¨ ¨ , Ratzeburger Allee 160, 23538 Lubeck , Germany Department of Obstetrics and Gynaecology, Medical University of Lubeck Received 13 June 1997; received in revised form 18 September 1997; accepted 12 January 1998
Abstract Vasa praevia is a rare complication of pregnancy associated with a high fetal morbidity and mortality. As planned caesarean section can circumvent fetal risks, early detection of vasa praevia is desirable. Antenatal diagnosis by ultrasound by visualisation of vasa praevia may be difficult by transvaginal sonography alone due to an unfavourable angle of insonation. Combination of transabdominal and transvaginal sonography is superior in imaging the placental type, location, insertion of the cord and vasa praevia. We present four cases of antepartum and one case of intrapartum diagnosis of vasa praevia in singleton pregnancies using transabdominal and transvaginal colour coded Doppler sonography. A bipartite placenta with normal cord insertion was found in three cases and with velamentous insertion of the cord in one case. One case had a partially membranous placenta with velamentous insertion of the cord. From the site of cord insertion fetal vessels were coursing over the internal cervical os and then continued in an amniotic sheet to the main placental mass on the opposite uterine wall. 1998 Elsevier Science Ireland Ltd. Keywords: Vasa praevia; Velamentous cord insertion; Amniotic sheet; Prenatal diagnosis; Colour coded Doppler sonography; Pulsed wave Doppler sonography
1. Introduction Vasa praevia is a rare complication of pregnancy occurring in the presence of velamentous insertion of the cord, succenturiate lobe of the placenta or a bipartite placenta [1]. The condition is characterised by the passage of fetal vessels between chorion and amnion, below the presenting part over the region of the internal os. The true incidence of vasa praevia is unknown, but estimated to range from 1:2000 to 1:5000 pregnancies [2,3]. Since the first description of ruptured vasa praevia in 1801 [4] mortality has remained virtually unchanged over the past years [3]. The associated fetal mortality may be due to exsanguination after ruptured membranes, or as*Corresponding author. Address for correspondence: Department of Obstetrics, Gynecology and Reproductive Sciences, University of Maryland Medical Center, 405 West Redwood Street, Baltimore, MD 21209, USA. Tel.: 11 410 3286475; fax: 11 410 3282849.
phyxia by occlusion of the vessels by the presenting part [5]. Antepartum diagnosis is rare despite improved diagnostic tools. However the use of grey scale ultrasound in combination with colour coded Doppler and pulsed wave Doppler can aid in making the diagnosis [6–9]. We present four cases of antepartum and one case of intrapartum diagnosis of vasa praevia in singleton pregnancies by colour coded Doppler sonography.
2. Case reports Five cases of vasa praevia were observed amongst 4822 singleton pregnancies (0.1%) delivered at a tertiary care facility from January 1st 1994 to December 31st 1996. Every patient receives a routine ultrasound examination on admission during which fetal size, position, placental location and amniotic fluid volume are assessed. If abnormalities are noticed a more detailed ultrasound examina-
0301-2115 / 98 / $19.00 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0301-2115( 98 )00026-8
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A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
tion for fetal and placental assessment is carried out. All ultrasound examinations were carried out using a 4 MHz sector probe or 7 MHz vaginal probe (Acuson XP 128 / 10 OB, Mountain View, Ca). Alternatively a 5 MHz curved array or 7.5 MHz vaginal probe were used (Logic 500, General Electric). After delivery each placenta and cord is systematically assessed for placental type, completeness, cord insertion and course of aberrant vessels. The cases presented include all patients in which vasa praevia was diagnosed during this time interval. The main data of these cases are summarised in Table 1. Four cases were diagnosed prenatally and one case during labour. In case 1 the patient was referred for evaluation of oligohydramnios at 4016 weeks gestation. Her obstetrician had noted frequent changes of fetal presentation between breech and cephalic during antenatal visits. The head was not engaged on abdominal palpation. The fetal heart tracing was normal. The umbilical cord was normal with two arteries and one vein, and the placenta was located on the anterior wall, reaching very close to the internal cervical os. A small succenturiate lobe was visualised on the posterior wall, again in close relation with the internal cervical os. Grey scale sonography revealed an irregularity of the fetal membranes in the lower pole, between the two placental masses. These structures were identified as blood vessels passing in front of the fetal head by transabdominal colour coded Doppler sonography (Fig. 1b). Pulsed wave Doppler sonography of the vessels showed patterns characteristic of arterial flow (Fig. 1c). Transvaginal colour coded Doppler sonography added little to making the diagnosis, as visualisation of the vessels was unsatisfactory. A diagnosis of a low lying placenta with a succenturiate lobe and vasa praevia was
made. Vaginal examination was deferred and a caesarean section was promptly performed and healthy newborn was delivered (Table 1). The main placental mass was anterior, with a small succenturiate lobe on the posterior wall of the uterus. The cord inserted peripherally into the main placenta and there were several vessels traversing the fetal membranes between the insertion of the cord and the succenturiate lobe (Fig. 2). In case 2 the patient was referred at 2915 weeks gestation for Doppler sonography for suspected uteroplacental insufficiency which was not confirmed. In the presence of a normal umbilical cord a low lying anterior placenta was demonstrated. Transabdominal and transvaginal colour coded Doppler sonography confirmed blood vessels passing over the internal os to a posterior succenturiate lobe, which had been suspected on B-mode sonography. The patient was seen at regular intervals for close fetal surveillance. The fetal heart tracing was normal at all times. At 3512 weeks gestation the patient had premature rupture of the membranes and a healthy female newborn was delivered by caesarean section. The situation of the placenta, succenturiate lobe and vasa praevia was identical to case one, however, the cord inserted centrally in the main placenta. In case 3 the patient was referred at 2910 weeks for evaluation of vaginal bleeding and premature labour. Again a low lying anterior placenta was noted the umbilical cord was normal. A retroplacental or retroamnial haematoma was not present. Transabdominal and transvaginal colour coded Doppler sonography showed blood vessels passing over the internal os to a posterior succenturiate lobe. The patient was admitted and commenced on i.v. tocolytics. The fetal heart tracing was normal at all
Table 1 Placental site, cord insertion and prenatal outcome in cases with placenta praevia Case
Obstetric history
Type of placenta and cord insertion
Gestational age at diagnosis
Mode and gestational age at delivery
Birthwt
Apgar
UA-pH
No 1
gravida 1, para 0
bipartite, marginal cord insertion
4016
358
9/10/10
7, 34
No 2
gravida 1, para 0
bipartite, normal cord insertion
2915
primary CS, 4016 primary CS, 3512
2380
10/10/10
7, 40
No 3
gravida 2, para 0
bipartite, normal cord insertion
2910
primary CS, 3415
220
8/10/10
7, 41
No 4
gravida 3, para 1
partially membranous placenta, velamentous insertion, single umbilical artery
2116
primary re-CS, 3311
166
6/8/9
7, 23
No 5
gravida 0, para 0
bipartite, velamentous insertion
3414
secondary CS, 3414
246
8/9/9
7, 29
Comment
Mode of primary US-diagnosis ta and tv
premature rupture of membranes premature rupture of membranes amniotic sheet with fetal vessels, oligo-hydramnios, preductal coarctation of the aorta
ta and tv
ta and tv
ta
tv
Key: CS 5 caesarean section, Apgar 5 Apgar scores at 1, 5 and 10 minutes, birthwt 5 birthweight in grams, mode of us diagnosis 5 mode of ultrasound diagnosis, ta 5 transabdominal, tv 5 transvaginal.
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
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Fig. 1. A sagittal view of the lower uterine segment obtained by transabdominal sonography shows the cervical canal (marked with arrows) and fetal head on the left. Vasa praevia can be seen coursing over the internal cervical os, identified by colour coded Doppler sonography (vessel coded in blue)(a). The venous blood flow in the opposite direction is coded in red (b). The flow velocity waveform obtained by placement of the pulsed wave Doppler gate in one of the aberrant vessels resembles umbilical arterial flow (c).
22
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
Fig. 1. (continued)
Fig. 2. This shows the placenta with the main placental mass on the left and a small succenturiate lobe on the right. Blood vessels can be seen to pass on the chorioamniotic membranes from the main placenta to the succenturiate lobe.
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
times. At 3415 weeks gestation immediate caesarean section was performed after premature rupture of the membranes and a healthy female newborn was delivered (Table 1). The placenta displayed a succenturiate lobe at the posterior wall with vasa praevia passing over the cervical os. The cord inserted centrally in the main anterior placenta. In case 4 the patient was referred for routine antenatal scanning for exclusion of fetal anomaly. In her first pregnancy caesarean section had been performed for premature labour at 31 weeks gestation. The postpartum period had been complicated by endo-myometritis and a curettage for retained products of conception. At this antenatal visit the fetus was in a transverse lie. The main placenta was situated anterior with a velamentous insertion of the cord on the posterior uterine wall. There was a single umbilical artery. Vasa praeviae were demonstrated by transabdominal colour coded Doppler to pass from the site of cord insertion coursing over the internal os to an amniotic sheet. This was confirmed by transvaginal colour coded Doppler. The amniotic sheet was situated between the right posterior and anterior uterine walls and the continuation of the vasa praeviae were passing in the free edge of the amniotic sheet towards to main anterior placenta (Fig. 3b). The patient was re-examined at weekly intervals. At 3311 weeks elective caesarean section was performed for progressive oligohydramnios and persistent transverse lie of the fetus. The fetal heart rate tracing had been normal throughout pregnancy. A male newborn was delivered and re-admitted at six weeks after developing preductal coarctation of the aorta. After operation the remaining clinical course was uneventful. Post-partum examination of the placenta confirmed the prenatal findings. In the fifth case the patient was admitted with premature labour at 3414 weeks gestation. After progressive dilatation of the cervix pulsating vessels were palpated in front of the presenting head at three centimetres. While the intrapartum fetal heart rate tracing had been normal, variable decelerations were observed at this time. Amnioscopy revealed vasa praevia which were confirmed by transvaginal colour coded Doppler flow mapping. Immediate caesarean section was performed and a healthy male newborn was delivered. Examination revealed a bipartite placenta with both masses at the anterior uterine wall. From a posterior velamentous insertion two sets of vessels were passing over the cervical os to each placental mass.
3. Discussion The umbilical cord inserts on the main placental mass in the majority of cases. A velamentous insertion of the cord on the chorioamniotic membranes rather than the main placenta results in a variable proportion of the umbilical vessels running between amnion and chorion, thus loosing
23
the protection of Whartons jelly [3,10,11]. Theories concerning the genesis of a velamentous cord insertion include abnormal fixation of yolk sac to chorion, aberrant body stalk insertion to a region of proliferating trophoblast away from the decidua basalis, abnormal primary implantation due to obliquity of the embryo during implantation and trophotropism [10,12]. A velamentous insertion of the cord is found in 0.24 to 1.25% of singleton pregnancies. In twin pregnancies one of the umbilical cords usually inserts more peripherally and thus a velamentous insertion is found in 8 to 18.5% [13–15], with an even higher incidence in twin pregnancies with fused placentas. In monochorionic diamniotic twin pregnancies complicated by twin–twin transfusion, the incidence of this anomalous cord insertion is significantly increased up to 63.6% [15]. In early pregnancy velamentous insertion of the cord is estimated to be present in 33% at the 12th and 26% between the 13th and 16th weeks of gestation [12]. A bilobed placenta as well as fetal anomalies including oesophageal atresia, obstructive uropathies, congenital hip translocation, asymmetrical head shape, ventricular septal defects and trisomy 21 are present in 5.9 to 8,5% of cases with velamentous cord insertion [17,18]. A single umbilical artery is found in 13% of cases [18]. Vasa praevia is the most significant problem arising with velamentous insertion of the cord if the placenta is lying in the lower uterine segment. Therefore, the antenatal diagnosis of a velamentous cord insertion should alert the examiner to the possible presence of vasa praevia. Of note is that only two cases in this series had vasa praevia in association with velamentous insertion. The likelihood of vasa praevia occurring in coexistence with a velamentous cord insertion was estimated at 1:50 in one series [14] while others state a 6% incidence in singleton pregnancies [16]. These unprotected vessels are predisposed to rupture at any time during pregnancy causing fetal exsanguination [3]. Although spontaneous rupture has been reported in intact and ruptured membranes [3,19–21], it usually occurs during amniotomy. As bleeding from vasa praevia is of fetal origin, associated fetal morbidity and mortality are extremely high ranging from 50–60% with intact, to 70– 100% with ruptured membranes [3,22–24]. Most diagnostic tests proposed, including testing of intrapartum blood loss by the Apt test [23,25] or determination of fetal haemoglobin in maternal serum will not have a major impact on fetal prognosis, which will remain poor with fetal haemorrhage. Detection of the aberrant vessels by palpation or amnioscopy may be difficult as well as it may precipitate haemorrhage. Antepartum diagnosis by real time ultrasound and pulsed wave Doppler sonography was first reported in 1987 [26]. However with the use of grey scale ultrasound careful scanning is required with a high index of suspicion to enable detection.
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A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
Fig. 3. This shows the amniotic sheet coursing from the posterior uterine wall up towards the main anterior placenta. Fetal blood vessels were demonstrated by transabdominal colour-Doppler (coded in red) (a) and confirmed as artery and vein by pulsed wave Doppler-sonography (b).
The additional use of colour coded Doppler sonography makes the detection of the aberrant vessels easier and also facilitates placement of the pulsed wave Doppler gate into the vessel thus improving the accuracy of diagnosis. Since the membranes usually have no flow the detection of blood
flow in a membrane can be considered pathognomic. The possibility to detect these vessels by colour coded Doppler ultrasound adds another important rationale for meticulous scanning of twin pregnancies. Usually prenatal diagnosis of vasa praevia had been in the presence of velamentous
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
insertion and mostly using transvaginal colour coded Doppler sonography [6–9,26–30]. In one case the diagnosis was made intrapartum and the baby was delivered without complications by caesarean section [9]. We would like to point out, that visualisation of vasa praevia may be difficult with transvaginal sonography alone. As seen in one case, vessels may run at an unfavourable insonation angle of 90 degrees to the relatively fixed transducer. If transvaginal visualisation by colour coded Doppler is not possible, the transabdominal route may allow for a more favourable insonation angle, and better visualisation of blood flow. Furthermore, only the combined use of transabdominal and transvaginal ultrasound allows the diagnosis of placental type, situation and the cord insertion. In addition, in one case we observed the presence of an amniotic sheet carrying fetal vessels similar to the case recently reported by Clerici and colleagues [30]. This diagnosis was only possible using the combined approach. Furthermore, pregnancy associated varicosities of the uterine vessels, may be mistaken for aberrant placental vessels. In this setting exact localisation by a combined approach may avoid an erroneous diagnosis of vasa praevia. The most important prerequisite for making the correct diagnosis however, is a high index of suspicion in the presence of known associations with vasa praevia. These include low-lying to marginal placenta, velamentous insertion of the cord, succenturiate lobes or multiple gestation [5,6]. In one of the cases presented the unengaged fetal head and the frequent changes in fetal presentation alerted the examiner to the possible presence of a low lying placenta. This report also stresses the fact that even in a low risk situation careful assessment of placentation can yield an unsuspected diagnosis. Evaluating exact placental position and cord insertion should be an integral part of a regular antenatal scan, which should be paid as much attention to as to the fetus. In the first and second trimester scan in particular, localisation of the cord insertion into the placental mass may be easier to identify than in the third trimester.
References [1] Evans GM. Vasa praevia. Br Med J 1952;2:1243. [2] Vago T, Caspi EL. Antepartum bleeding due to injury to velamentous insertion of placental vessels. Obstet Gynecol 1962;20:671–4. [3] Kouyoumadjian A. Velamentous insertion of the umbilical cord. Obstet Gynecol 1980;56:737–42. [4] Lobstein. Arch de l’art des accouchments. Strasbourg 1801. 320–28. [5] Dougall A, Baird CH. Vasa praevia—report of three cases and review of the literature. Br J Obstet Gynaecol 1987;94:712–5.
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[6] Harding JA, Lewis DF, Major CA, Crade M, Patel J, Nageotte MP. Colour flow Doppler—a useful tool in the diagnosis of vasa praevia. Am J Obstet Gynecol 1990;163:1566–8. [7] Nelson LH, Melone PJ, King M. Diagnosis of vasa previa with transvaginal and colour flow Doppler ultrasound. Obstet Gynecol 1990;76:506–9. [8] Hsieh FJ, Chen HF, Ko TM, Hsieh CY, Chen HY. Antenatal diagnosis of vasa praevia by colour flow mapping. J Ultrasound Med 1991;10:397–9. [9] Arts H, van Eyck J. Antenatal diagnosis of vasa previa by transvaginal colour Doppler sonography. Ultrasound Obstet Gynecol 1993;3:276–8. [10] Benirschke K, Kaufmann P. Pathology of the human placenta. New York: Springer, 1990:200–4. [11] Fox, H. Pathology of the placenta. Philadelphia: WB Saunders, 1978:434–7. [12] Monie IW. Velamentous insertion of the cord in early pregnancy. Am J Obstet Gynecol 1965;93:276–81. [13] Torrey WE. Vasa praevia. Am J Obstet Gynecol 1952;63:146–52. [14] Quek SP, Tan KL. Vasa praevia. Aust NZ J Obstet Gynecol 1972;12:206–9. [15] Fries MH, Goldstein RB, Kilpatrick SJ, Golbus MS, Callen PW, Filly RA. The role of velamentous cord insertion in the etiology of twin-twin transfusion syndrome. Obstet Gynecol 1993;81:569–74. [16] Paavonen J, Jouttunnpaa K, Kangasluooma P. Velamentous insertion of the cord and vasa previa. Int J Gynaecol Obstet 1984;22:207–11. [17] Bjoro K. Vascular anomalies of the umbilical cord. II. Perinatal and pediatric implications. Early Hum Dev 1983;8:279–87. [18] Robinson LK, Jones KL, Benirschke K. The nature of the structural defects associated with velamentous and marginal insertion of the umbilical cord. Am J Obstet Gynecol 1983;146:191–3. [19] Bjoro K. Vascular anomalies of the umbilical cord. I. Obstetric implications. Early Hum Dev 1983;8:119–27. [20] Carp HJA, Mashiach S, Serr DM. Vasa previa: a major complication and its management. Obstet Gynecol 1979;53:273–5. [21] Porter CC, Davies NJ, Gerden AS. Fetal death due to spontaneous rupture of vasa praevia with intact membranes. Int J Obstet Gynaecol 1991;11:349–50. [22] Naftolin F, Mimshell DR. Vasa praevia. Report of three cases. Obstet Gynecol 1965;26:561–5. [23] Pent D. Vasa praevia. Am J Obstet Gynecol 1979;134:151–5. [24] Antoine C, Young BK, Silverman F et al. Sinusoidal fetal heart rate pattern with vasa previa in twin pregnancy. J Reprod Med 1982;27:295–300. [25] Apt L, Darney W. Meelena neonatorum: the swallowed blood syndrome: a simple test for differentiation of adult and fetal hemoglobin in bloody stool. J Pediatr 1955;47:6–12. [26] Fleischer AC, Kepple DM. Transvaginal colour Doppler sonography. Philadelphia: Lippincott, 1992:273–5. [27] Gianopoulos J, Carver T, Tomich PG, Karlman R, Gadwood K. Diagnosis of vasa previa with ultrasonography. Obstet Gynecol 1987;69:488–91. [28] Hurley VA. The antenatal diagosis of vasa praevia: the role of ultrasound. Aust NZ J Obstet Gynecol 1988;28:177–9. [29] Daly-Jones E, Hollingsworth J, Sepulveda W. Vasa praevia: second trimester diagnosis using colour flow imaging. Br J Obstet Gynaecol 1996;103:284–6. [30] Clerici G, Burnelli L, Lauro V, Pilu GL, Di Renzo GC. Prenatal diagnosis of vasa previa presenting as amniotic band. ‘A not so innocent amniotic band’. Ultrasound Obstet Gynecol 1996;7:61–3.
Ante- and intrapartum diagnosis of vasa praevia in singleton pregnancies by colour coded Doppler sonography Ahmet Alexander Baschat*, Ulrich Gembruch ¨ ¨ , Ratzeburger Allee 160, 23538 Lubeck , Germany Department of Obstetrics and Gynaecology, Medical University of Lubeck Received 13 June 1997; received in revised form 18 September 1997; accepted 12 January 1998
Abstract Vasa praevia is a rare complication of pregnancy associated with a high fetal morbidity and mortality. As planned caesarean section can circumvent fetal risks, early detection of vasa praevia is desirable. Antenatal diagnosis by ultrasound by visualisation of vasa praevia may be difficult by transvaginal sonography alone due to an unfavourable angle of insonation. Combination of transabdominal and transvaginal sonography is superior in imaging the placental type, location, insertion of the cord and vasa praevia. We present four cases of antepartum and one case of intrapartum diagnosis of vasa praevia in singleton pregnancies using transabdominal and transvaginal colour coded Doppler sonography. A bipartite placenta with normal cord insertion was found in three cases and with velamentous insertion of the cord in one case. One case had a partially membranous placenta with velamentous insertion of the cord. From the site of cord insertion fetal vessels were coursing over the internal cervical os and then continued in an amniotic sheet to the main placental mass on the opposite uterine wall. 1998 Elsevier Science Ireland Ltd. Keywords: Vasa praevia; Velamentous cord insertion; Amniotic sheet; Prenatal diagnosis; Colour coded Doppler sonography; Pulsed wave Doppler sonography
1. Introduction Vasa praevia is a rare complication of pregnancy occurring in the presence of velamentous insertion of the cord, succenturiate lobe of the placenta or a bipartite placenta [1]. The condition is characterised by the passage of fetal vessels between chorion and amnion, below the presenting part over the region of the internal os. The true incidence of vasa praevia is unknown, but estimated to range from 1:2000 to 1:5000 pregnancies [2,3]. Since the first description of ruptured vasa praevia in 1801 [4] mortality has remained virtually unchanged over the past years [3]. The associated fetal mortality may be due to exsanguination after ruptured membranes, or as*Corresponding author. Address for correspondence: Department of Obstetrics, Gynecology and Reproductive Sciences, University of Maryland Medical Center, 405 West Redwood Street, Baltimore, MD 21209, USA. Tel.: 11 410 3286475; fax: 11 410 3282849.
phyxia by occlusion of the vessels by the presenting part [5]. Antepartum diagnosis is rare despite improved diagnostic tools. However the use of grey scale ultrasound in combination with colour coded Doppler and pulsed wave Doppler can aid in making the diagnosis [6–9]. We present four cases of antepartum and one case of intrapartum diagnosis of vasa praevia in singleton pregnancies by colour coded Doppler sonography.
2. Case reports Five cases of vasa praevia were observed amongst 4822 singleton pregnancies (0.1%) delivered at a tertiary care facility from January 1st 1994 to December 31st 1996. Every patient receives a routine ultrasound examination on admission during which fetal size, position, placental location and amniotic fluid volume are assessed. If abnormalities are noticed a more detailed ultrasound examina-
0301-2115 / 98 / $19.00 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0301-2115( 98 )00026-8
20
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
tion for fetal and placental assessment is carried out. All ultrasound examinations were carried out using a 4 MHz sector probe or 7 MHz vaginal probe (Acuson XP 128 / 10 OB, Mountain View, Ca). Alternatively a 5 MHz curved array or 7.5 MHz vaginal probe were used (Logic 500, General Electric). After delivery each placenta and cord is systematically assessed for placental type, completeness, cord insertion and course of aberrant vessels. The cases presented include all patients in which vasa praevia was diagnosed during this time interval. The main data of these cases are summarised in Table 1. Four cases were diagnosed prenatally and one case during labour. In case 1 the patient was referred for evaluation of oligohydramnios at 4016 weeks gestation. Her obstetrician had noted frequent changes of fetal presentation between breech and cephalic during antenatal visits. The head was not engaged on abdominal palpation. The fetal heart tracing was normal. The umbilical cord was normal with two arteries and one vein, and the placenta was located on the anterior wall, reaching very close to the internal cervical os. A small succenturiate lobe was visualised on the posterior wall, again in close relation with the internal cervical os. Grey scale sonography revealed an irregularity of the fetal membranes in the lower pole, between the two placental masses. These structures were identified as blood vessels passing in front of the fetal head by transabdominal colour coded Doppler sonography (Fig. 1b). Pulsed wave Doppler sonography of the vessels showed patterns characteristic of arterial flow (Fig. 1c). Transvaginal colour coded Doppler sonography added little to making the diagnosis, as visualisation of the vessels was unsatisfactory. A diagnosis of a low lying placenta with a succenturiate lobe and vasa praevia was
made. Vaginal examination was deferred and a caesarean section was promptly performed and healthy newborn was delivered (Table 1). The main placental mass was anterior, with a small succenturiate lobe on the posterior wall of the uterus. The cord inserted peripherally into the main placenta and there were several vessels traversing the fetal membranes between the insertion of the cord and the succenturiate lobe (Fig. 2). In case 2 the patient was referred at 2915 weeks gestation for Doppler sonography for suspected uteroplacental insufficiency which was not confirmed. In the presence of a normal umbilical cord a low lying anterior placenta was demonstrated. Transabdominal and transvaginal colour coded Doppler sonography confirmed blood vessels passing over the internal os to a posterior succenturiate lobe, which had been suspected on B-mode sonography. The patient was seen at regular intervals for close fetal surveillance. The fetal heart tracing was normal at all times. At 3512 weeks gestation the patient had premature rupture of the membranes and a healthy female newborn was delivered by caesarean section. The situation of the placenta, succenturiate lobe and vasa praevia was identical to case one, however, the cord inserted centrally in the main placenta. In case 3 the patient was referred at 2910 weeks for evaluation of vaginal bleeding and premature labour. Again a low lying anterior placenta was noted the umbilical cord was normal. A retroplacental or retroamnial haematoma was not present. Transabdominal and transvaginal colour coded Doppler sonography showed blood vessels passing over the internal os to a posterior succenturiate lobe. The patient was admitted and commenced on i.v. tocolytics. The fetal heart tracing was normal at all
Table 1 Placental site, cord insertion and prenatal outcome in cases with placenta praevia Case
Obstetric history
Type of placenta and cord insertion
Gestational age at diagnosis
Mode and gestational age at delivery
Birthwt
Apgar
UA-pH
No 1
gravida 1, para 0
bipartite, marginal cord insertion
4016
358
9/10/10
7, 34
No 2
gravida 1, para 0
bipartite, normal cord insertion
2915
primary CS, 4016 primary CS, 3512
2380
10/10/10
7, 40
No 3
gravida 2, para 0
bipartite, normal cord insertion
2910
primary CS, 3415
220
8/10/10
7, 41
No 4
gravida 3, para 1
partially membranous placenta, velamentous insertion, single umbilical artery
2116
primary re-CS, 3311
166
6/8/9
7, 23
No 5
gravida 0, para 0
bipartite, velamentous insertion
3414
secondary CS, 3414
246
8/9/9
7, 29
Comment
Mode of primary US-diagnosis ta and tv
premature rupture of membranes premature rupture of membranes amniotic sheet with fetal vessels, oligo-hydramnios, preductal coarctation of the aorta
ta and tv
ta and tv
ta
tv
Key: CS 5 caesarean section, Apgar 5 Apgar scores at 1, 5 and 10 minutes, birthwt 5 birthweight in grams, mode of us diagnosis 5 mode of ultrasound diagnosis, ta 5 transabdominal, tv 5 transvaginal.
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
21
Fig. 1. A sagittal view of the lower uterine segment obtained by transabdominal sonography shows the cervical canal (marked with arrows) and fetal head on the left. Vasa praevia can be seen coursing over the internal cervical os, identified by colour coded Doppler sonography (vessel coded in blue)(a). The venous blood flow in the opposite direction is coded in red (b). The flow velocity waveform obtained by placement of the pulsed wave Doppler gate in one of the aberrant vessels resembles umbilical arterial flow (c).
22
A. A. Baschat, U. Gembruch / European Journal of Obstetrics & Gynecology and Reproductive Biology 79 (1998) 19 – 25
Fig. 1. (continued)
Fig. 2. This shows the placenta with the main placental mass on the left and a small succenturiate lobe on the right. Blood vessels can be seen to pass on the chorioamniotic membranes from the main placenta to the succenturiate lobe.
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times. At 3415 weeks gestation immediate caesarean section was performed after premature rupture of the membranes and a healthy female newborn was delivered (Table 1). The placenta displayed a succenturiate lobe at the posterior wall with vasa praevia passing over the cervical os. The cord inserted centrally in the main anterior placenta. In case 4 the patient was referred for routine antenatal scanning for exclusion of fetal anomaly. In her first pregnancy caesarean section had been performed for premature labour at 31 weeks gestation. The postpartum period had been complicated by endo-myometritis and a curettage for retained products of conception. At this antenatal visit the fetus was in a transverse lie. The main placenta was situated anterior with a velamentous insertion of the cord on the posterior uterine wall. There was a single umbilical artery. Vasa praeviae were demonstrated by transabdominal colour coded Doppler to pass from the site of cord insertion coursing over the internal os to an amniotic sheet. This was confirmed by transvaginal colour coded Doppler. The amniotic sheet was situated between the right posterior and anterior uterine walls and the continuation of the vasa praeviae were passing in the free edge of the amniotic sheet towards to main anterior placenta (Fig. 3b). The patient was re-examined at weekly intervals. At 3311 weeks elective caesarean section was performed for progressive oligohydramnios and persistent transverse lie of the fetus. The fetal heart rate tracing had been normal throughout pregnancy. A male newborn was delivered and re-admitted at six weeks after developing preductal coarctation of the aorta. After operation the remaining clinical course was uneventful. Post-partum examination of the placenta confirmed the prenatal findings. In the fifth case the patient was admitted with premature labour at 3414 weeks gestation. After progressive dilatation of the cervix pulsating vessels were palpated in front of the presenting head at three centimetres. While the intrapartum fetal heart rate tracing had been normal, variable decelerations were observed at this time. Amnioscopy revealed vasa praevia which were confirmed by transvaginal colour coded Doppler flow mapping. Immediate caesarean section was performed and a healthy male newborn was delivered. Examination revealed a bipartite placenta with both masses at the anterior uterine wall. From a posterior velamentous insertion two sets of vessels were passing over the cervical os to each placental mass.
3. Discussion The umbilical cord inserts on the main placental mass in the majority of cases. A velamentous insertion of the cord on the chorioamniotic membranes rather than the main placenta results in a variable proportion of the umbilical vessels running between amnion and chorion, thus loosing
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the protection of Whartons jelly [3,10,11]. Theories concerning the genesis of a velamentous cord insertion include abnormal fixation of yolk sac to chorion, aberrant body stalk insertion to a region of proliferating trophoblast away from the decidua basalis, abnormal primary implantation due to obliquity of the embryo during implantation and trophotropism [10,12]. A velamentous insertion of the cord is found in 0.24 to 1.25% of singleton pregnancies. In twin pregnancies one of the umbilical cords usually inserts more peripherally and thus a velamentous insertion is found in 8 to 18.5% [13–15], with an even higher incidence in twin pregnancies with fused placentas. In monochorionic diamniotic twin pregnancies complicated by twin–twin transfusion, the incidence of this anomalous cord insertion is significantly increased up to 63.6% [15]. In early pregnancy velamentous insertion of the cord is estimated to be present in 33% at the 12th and 26% between the 13th and 16th weeks of gestation [12]. A bilobed placenta as well as fetal anomalies including oesophageal atresia, obstructive uropathies, congenital hip translocation, asymmetrical head shape, ventricular septal defects and trisomy 21 are present in 5.9 to 8,5% of cases with velamentous cord insertion [17,18]. A single umbilical artery is found in 13% of cases [18]. Vasa praevia is the most significant problem arising with velamentous insertion of the cord if the placenta is lying in the lower uterine segment. Therefore, the antenatal diagnosis of a velamentous cord insertion should alert the examiner to the possible presence of vasa praevia. Of note is that only two cases in this series had vasa praevia in association with velamentous insertion. The likelihood of vasa praevia occurring in coexistence with a velamentous cord insertion was estimated at 1:50 in one series [14] while others state a 6% incidence in singleton pregnancies [16]. These unprotected vessels are predisposed to rupture at any time during pregnancy causing fetal exsanguination [3]. Although spontaneous rupture has been reported in intact and ruptured membranes [3,19–21], it usually occurs during amniotomy. As bleeding from vasa praevia is of fetal origin, associated fetal morbidity and mortality are extremely high ranging from 50–60% with intact, to 70– 100% with ruptured membranes [3,22–24]. Most diagnostic tests proposed, including testing of intrapartum blood loss by the Apt test [23,25] or determination of fetal haemoglobin in maternal serum will not have a major impact on fetal prognosis, which will remain poor with fetal haemorrhage. Detection of the aberrant vessels by palpation or amnioscopy may be difficult as well as it may precipitate haemorrhage. Antepartum diagnosis by real time ultrasound and pulsed wave Doppler sonography was first reported in 1987 [26]. However with the use of grey scale ultrasound careful scanning is required with a high index of suspicion to enable detection.
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Fig. 3. This shows the amniotic sheet coursing from the posterior uterine wall up towards the main anterior placenta. Fetal blood vessels were demonstrated by transabdominal colour-Doppler (coded in red) (a) and confirmed as artery and vein by pulsed wave Doppler-sonography (b).
The additional use of colour coded Doppler sonography makes the detection of the aberrant vessels easier and also facilitates placement of the pulsed wave Doppler gate into the vessel thus improving the accuracy of diagnosis. Since the membranes usually have no flow the detection of blood
flow in a membrane can be considered pathognomic. The possibility to detect these vessels by colour coded Doppler ultrasound adds another important rationale for meticulous scanning of twin pregnancies. Usually prenatal diagnosis of vasa praevia had been in the presence of velamentous
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insertion and mostly using transvaginal colour coded Doppler sonography [6–9,26–30]. In one case the diagnosis was made intrapartum and the baby was delivered without complications by caesarean section [9]. We would like to point out, that visualisation of vasa praevia may be difficult with transvaginal sonography alone. As seen in one case, vessels may run at an unfavourable insonation angle of 90 degrees to the relatively fixed transducer. If transvaginal visualisation by colour coded Doppler is not possible, the transabdominal route may allow for a more favourable insonation angle, and better visualisation of blood flow. Furthermore, only the combined use of transabdominal and transvaginal ultrasound allows the diagnosis of placental type, situation and the cord insertion. In addition, in one case we observed the presence of an amniotic sheet carrying fetal vessels similar to the case recently reported by Clerici and colleagues [30]. This diagnosis was only possible using the combined approach. Furthermore, pregnancy associated varicosities of the uterine vessels, may be mistaken for aberrant placental vessels. In this setting exact localisation by a combined approach may avoid an erroneous diagnosis of vasa praevia. The most important prerequisite for making the correct diagnosis however, is a high index of suspicion in the presence of known associations with vasa praevia. These include low-lying to marginal placenta, velamentous insertion of the cord, succenturiate lobes or multiple gestation [5,6]. In one of the cases presented the unengaged fetal head and the frequent changes in fetal presentation alerted the examiner to the possible presence of a low lying placenta. This report also stresses the fact that even in a low risk situation careful assessment of placentation can yield an unsuspected diagnosis. Evaluating exact placental position and cord insertion should be an integral part of a regular antenatal scan, which should be paid as much attention to as to the fetus. In the first and second trimester scan in particular, localisation of the cord insertion into the placental mass may be easier to identify than in the third trimester.
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