It should be done at 32–34 weeks of gestation for women with twins.

The recommended time of testing is 3–5 weeks prior to the anticipated delivery date- therefore  35–37 weeks of gestation in singleton pregnancies with no risk factors for preterm delivery.

A systematic review reported that women with one, two, or three or more previous caesarean deliveries experience a 1%, 1.7% or 2.8% risk of placenta previa in a subsequent pregnancy. ( Source- Birth After Previous
Caesarean Birth Green-top Guideline No. 45 ).

Assisted reproductive technology ( RR- 3.71, OR 2.67)and maternal smoking ( OR 1.42)  increase the risk of placenta praevia.

The likelihood of maternal GBS carriage in this pregnancy is 50%.
What should be done?- Discuss the options- a. Intrapartum antibiotic prophylaxis ( IAP).
b. Bacteriological testing in late pregnancy and the offer of IAP if still positive. ( This is the only group of women who are eligible for GBS screening funded by NHS)

In the event of an intrauterine death (IUD), where no sample can be obtained from the baby, an appropriate dose of prophylactic anti-D Ig should be administered within
72 h of the diagnosis of IUD, irrespective of the time of subsequent delivery.

A dose of 250 IU anti-D immunoglobulin should be sufficient to cover up to five adult therapeutic doses of D positive platelets given within a 6-week period.

In severely thrombocytopenic patients with platelet count of?30 × 10^9/L, anti-D Ig should be given subcutaneously, or IV.

When testing for GBS carrier status, a swab should be taken from the lower vagina and the anorectum.

A single swab (vagina then anorectum) or two different swabs can be used.

Antenatal treatment for vaginal or rectal colonisation does not reduce the likelihood of GBS colonisation at the time of delivery and so is not indicated in this situation.

IAP should be offered to GBS-colonised women

Routine ultrasound screening is not useful. Selective ultrasound screening can be considered for women with breech presentation at term who are considering vaginal birth.

Successful VBAC is more likely among women with previous caesarean for
fetal malpresentation (84%) compared with women with previous caesarean for either labour dystocia (64%) or fetal distress (73%) indications.

Previous vaginal delivery, particularly previous VBAC, is the single best predictor of successful VBAC and is associated with a planned VBAC success rate of 85–90%.

Previous vaginal delivery is also independently associated
with a reduced risk of uterine rupture.

• No screening test is entirely accurate.
• 17% to 25% of women who have a positive swab at 35–37 weeks of gestation will be GBS negative at delivery.
•  5% to 7% of women who are GBS negative at 35–37 weeks of gestation will be GBS positive at delivery.
• Many of the babies who are severely affected from GBS infection are born prematurely, before the suggested time for screening.

This is GBS bacteruria. GBS bacteriuria is associated with a higher risk of chorioamnionitis and neonatal disease. Women with GBS bacteriuria should be offered IAP.

Women with GBS urinary tract infection (growth of greater than 10^5 cfu/ml) during pregnancy should receive appropriate treatment at the time of diagnosis as well as IAP. 

For potentially sensitising events after 20weeks gestation,
a minimum anti-D Ig dose of 500 IU should be administered within 72 h of the event.

It is not necessary to administer anti-D Ig to D negative females without childbearing potential, or males who receive D positive platelets.

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