ANTEPARTUM HAEMORRHAGE - APH

PLACENTA PRAEVIA

 

 

Screening and diagnosis of placenta praevia.

    

 

While clinical acumen remains vitally important in suspecting and managing placenta praevia, the definitive diagnoses of most low-lying placentas is now achieved with ultrasound imaging. Clinical suspicion should, however, be raised in any woman with vaginal bleeding and a high presenting part or an abnormal lie, irrespective of previous imaging results.

Transvaginal ultrasound is safe in the presence of placenta praevia and is more accurate than transabdominal ultrasound in locating the placenta. Numerous prospective observational studies have used transvaginal ultrasound scanning (TVS) to diagnose placenta praevia and none has experienced any haemorrhagic complications, thus confirming its safety.9001, 9601, 9701, 0201There is still only one small RCT which exists comparing transabdominal scans (TAS) and TVS for placenta praevia that supports this safety profile.9201

With the lower segment still unformed in the second trimester, screening for future placenta praevia at this time is inevitably associated with false positives, as not all low lying placentas will persist and this is especially so when TAS is employed. TVS can improve on this. In the second trimester,26?60% of cases of low-lying placenta diagnosed by TAS are reclassified by TVS.9701 Leerentveld et al9001 demonstrated high levels of accuracy of TVS in predicting placenta praevia in 100 women suspected of having a low-lying placenta in the second and third trimester (sensitivity 87.5%, specificity 98.8%, positive predictive value 93.3%, negative predictive value 97.6%, false negative rate 2.33%).

Magnetic resonance imaging (MRI) has been reported in the diagnosis of placenta praevia where TAS images have been unsatisfactory.8601 MRI has the advantage of being possible without a full bladder and is an objective test, removing operator error. It is particularly useful in imaging posterior placentas but has not been subject to comparison with TVS and can only be recommended for use in a research context at this stage.

A reasonable antenatal imaging policy is to perform a transvaginal ultrasound scan on all women in whom a low-lying placenta is suspected from their transabdominal anomaly scan (at approximately 20?24 weeks) to reduce the numbers of those for whom follow-up will be needed. A further transvaginal scan is required for all women whose placenta reaches or overlaps the cervical os at their anomaly scan as follows:

  • Women who bleed should be managed individually according to their needs.
  • In cases of asymptomatic suspected minor praevia, follow-up imaging can be left until 36 weeks.
  • In cases with asymptomatic suspected major placenta praevia, a transvaginal ultrasound scan
  • should be performed at 32 weeks, to clarify the diagnosis and allow planning for third-trimester
  • management and delivery.

Placental migration occurs during the second and third trimesters,0001,0201,0202 owing to the development of the lower uterine segment, but it is less likely if the placenta is posterior0002 or if there has been a previous caesarean section.0201 A retrospective review of 714 women with placenta praevia found that, even with a marginal ?praevia? at 20?23 weeks (i.e. the edge of the placenta reached the internal cervical os), the chance of persistence of the placenta praevia requiring abdominal delivery was 11% with no uterine scar and 50% with a previous caesarean section.0201 In another study of 55 women with a placenta reaching or overlapping the cervical os at 18?23 weeks diagnosed by transvaginal sonography, only five had placenta praevia at birth and in all these cases the edge of the placenta had overlapped 15 mm over the os. Migration is still possible, with a 50% chance of resolution if the placenta covers the os at 20 weeks.0201

For these reasons, a third-trimester follow-up scan is needed to confirm the diagnosis and plan further care. In the case of asymptomatic women in whom the placental edge has only reached or just overlapped the cervical os at the second trimester scan, with anticipated minor placenta praevia, a scan should be performed at 36 weeks. Those suspected of major placenta praevia require clarification of the diagnosis earlier to enable counselling and careful planning. This should be taken into account in the timing of the follow-up scan, which should be conducted at around 32 weeks. Placentas still diagnosed as complete praevia at this gestation remain so in 90% of cases.0201

 

 

Women's Health


Thank you for choosing to visit us.


This is the personal website of David A Viniker MD FRCOG, Consultant Obstetrician and Gynaecologist at Whipps Cross University Hospital, London - Specialist Interests - Reproductive Medicine including Infertility, PCOS, PMS, Menopause and HRT.

I do hope that you find the answers to your women's health questions in the patient information and medical advice provided.


Women's Health



women's health

 

Thank you for choosing to visit us.


This is the personal website of David A Viniker MD FRCOG, Consultant Obstetrician and Gynaecologist at Whipps Cross University Hospital, London - Specialist Interests - Reproductive Medicine including Infertility, PCOS, PMS, Menopause and HRT.

I do hope that you find the answers to your women's health questions in the patient information and medical advice provided. If you still have unanswered questions, please consider entering them into one of our forums and I will try to assist you.  





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