Vasa Previa

Author Information

Raut VS*, Jain N**, Jain P**, Velankar K**
(* Consultant, ** Resident, Department of Obstetrics and Gynecology, Dr. L.H. Hiranandani Hospital, Mumbai, India.)

Abstract

Vasa previa is an uncommon but catastrophic obstetrical complication which often goes undiagnosed. High index of suspicion is required to prevent fetal morbidity and mortality. Because of unanticipated sudden fetal demise, this is one of the most dreaded events in modern obstetrics. The suspicion of vasa previa in a patient with low lying placenta is highlighted in this case report. A primigravida with 38 weeks of gestation with placenta 4 cm away from the internal os presented in active labour with 4 cm dilation and good fetal heart tracing. The patient had spontaneous rupture of membranes along with a large bout of vaginal bleeding with persistent fetal bradycardia at 60 beats per minute resulting in emergency cesarean section.

Introduction

Vasa previa is an uncommon type of placental and cord anatomy where fetal vessels course through the membranes over the internal os and in front of the fetal presenting part. The vessels are unprotected either by placental tissue or the umbilical cord [1]. These patients present with painless vaginal bleeding at the time of spontaneous or artificial rupture of membranes. In 50 - 60 % of cases, fetal mortality may occur by immediate fetal distress because of compression of vessels by presenting part [2] and mortality can be as high as 75 - 100% [3], when the vessels are torn following spontaneous rupture of membranes or amniotomy, leading to fetal hemorrhage[1].

Case Report
A 33 year old, registered primigravida with regular follow up, with natural conception, came with labor pain at 38 weeks 3 days of gestation. Her ultrasonography (USG) at 12 weeks showed a low lying placenta, covering the internal os. Subsequent USG at 19 weeks showed a low lying placenta, 7 mm away from internal os. She was admitted at 34 weeks with antepartum haemorrhage and was managed conservatively. Her USG at 36 weeks revealed anterolateral low lying placenta, 4 cm away from the internal os. Examination revealed the fetus to be in vertex presentation with 2 uterine contractions lasting for 15 seconds in every 10 minutes and 4 cm cervical dilatation with intact membranes and good fetal heart tracing.
As the placenta was 4 cm away from the internal os and the patient was in active labor with a reactive NST, decision for trial of labor was taken. The patient and her husband were explained that at any time during the course of labor if she develops bleeding per vaginum, patient will be taken for cesarean section. She was kept on continuous fetal monitoring and was closely observed for signs of distress. One hour after the admission she suddenly had a large bout of bleeding per vaginum with fetal heart decelerations till 60 beats per minute that persisted. In view of fetal distress emergency cesarean section was performed.
A male baby weighing 3.8 kg was delivered with Apgar score of 1, 2 and 7 at birth, 1 minute and 5 minutes of life respectively after resuscitation. Baby was grossly pale at birth and was shifted to NICU. Baby’s hemoglobin was 10.40 gm % at birth. 80 ml packed red blood cells were transfused within 1 hour of birth to the baby. On day 4 hemoglobin was 13.40 gm%, when the mother and the baby were discharged. The maternal condition remained stable throughout;, hemoglobin was 12.5 gm % pre- delivery and 12 gm % post- delivery.
As after the bout of bleeding, there was sudden and persistent fetal bradycardia, and as the fetus looked grossly pale, we examined the placenta in detail which revealed a bilobed placenta with velamentous insertion of cord, confirming the diagnosis of vasa previa.


Figure 1. Bilobed placenta.


Figure 2. Velamentous insertion of cord.

Discussion

The incidence of vasa previa is about 1 in 2500 deliveries [3]. If there is a velamentous insertion of the umbilical cord with the presence of low lying placenta, this incidence rises to 1 in 50. The risk factors for vasa previa include conditions associated with blood vessels that are in close proximity to or over the cervix, like placenta previa [2,4,5,6], multiple pregnancies [3] and multilobed placenta and velamentous insertion [7].
Before the advent of obstetric ultrasound, vasa previa was rarely detected in asymptomatic women. Oftentimes, an emergency cesarean section was done for acute profound fetal distress and only at CS was vasa previa discovered [7,8]. Diagnosis of vasa previa may be reached by sonography, magnetic resonance imaging (MRI), amnioscopy, by palpation of vessels on digital vaginal examination or by identifying fetal blood in vagina [1,9]. In all cases with risk factors for vasa previa, targeted transvaginal ultrasound examination of the lower uterine segment and cervical os using colour Doppler should be done; this is the recommendation of numerous authors.[1,6,7,9,10,11,12,13]
Diagnostic criteria on transvaginal ultrasound include the presence of a sonolucent linear area over the internal os, with sparse or absent Wharton’s jelly. Only combined transabdominal and transvaginal ultrasound [11,13] and color Doppler allows the diagnosis of placental type and location, and the cord insertion; however, many cases are not diagnosed. Not reaching the diagnosis of vasa previa is still acceptable, because even under the best circumstances the false negative rate is high [3].
Canadian Task Force on Preventive Health Care (2009) has laid down following guidelines in order to improve the diagnosis of vasa previa [1]:
• If there is a low lying placenta at the routine second trimester ultrasound, an evaluation for placental cord insertion should be performed. 
• If vasa previa is suspected, transvaginal ultrasound and color Doppler may be used to aid diagnosis. Even with the use of transvaginal ultrasound and color Doppler, vasa previa may be missed.
• While antenatal diagnosis optimizes outcome among women with known vasa previa, undiagnosed cases will still occur, presenting in labor with variable decelerations and palpable vessels through intact membranes, or intrapartum vaginal bleeding along with acute fetal distress at the time of membrane rupture.  
The Apt test and haemoglobin electrophoresis [1,13] can be used to detect the presence of fetal haemoglobin when patients present with vaginal bleeding; however, the sudden and unexpected way in which the bleeding occurs limits the use of this test. Some workers have used MRI to diagnose vasa previa, but is often impractical for diagnosis, especially in the emergecy situation. 
Conclusion
Every case of placenta previa should be screened with high resolution USG and Doppler for vasa previa. While antenatal diagnosis optimizes outcome among women with known vasa previa, undiagnosed cases will still occur. Hence, a high index of suspicion is still needed, should there be fetal heart deceleration or vaginal bleeding immediately after amniotomy. However, the fetal outcome in a case of vasa previa diagnosed clinically is almost invariably poor.

References
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Citation

Raut VS, Jain N, Jain P, Velankar K. Vasa Previa. JPGO 2015. Volume 3 No. 5. Available from: http://www.jpgo.org/2016/05/vasa-previa.html