On successfully completing this topic, you will be able to:
understand how to assess suitability for vaginal delivery
understand how to safely manage appropriate vaginal twin deliveries.
Introduction
Dizygous twinning rates vary enormously depending on age, parity, racial background and assisted-conception techniques. The incidence of twin pregnancies continues to increase, largely due to assisted reproduction techniques, giving a multiple birth rate of 16/1000 maternities in England and Wales in 2009. Monozygous twinning rates are relatively constant, with an incidence of 3.5/1000 births. Overall maternal and perinatal mortality and morbidity are higher in multiple gestations than in singletons. Premature delivery and the complications of prematurity are the main contributors to adverse outcomes. Other factors contributing to the risk are: intrauterine growth restriction; congenital anomalies; malpresentation; cord prolapse; and premature separation of the placenta.
The use of routine antenatal ultrasound assessment has facilitated the diagnosis of multiple gestations. Women with multiple fetuses who attend for antenatal care should have the chorionicity of the pregnancy determined early in pregnancy and then have serial growth scans as specified in the recent NICE and RCOG Greentop guidelines on the antenatal care of multiple pregnancies.1,2 It is recommended that monochorionic twins are delivered after 36+0 weeks following a course of antenatal steroids, and dichorionic twins are delivered after 37+0 weeks.
A meta-analysis of the management of twin delivery did not find significant differences in outcome, in terms of mortality or neonatal morbidity, when comparing policies of planned vaginal delivery against planned CS. A cohort study of 2890 twin pairs delivered after 36 weeks of gestation found that there were no deaths in those twins delivered by CS, but nine second-twin deaths in those delivered vaginally. An international, multicentre, RCT (the Twin Birth Study) of 2400 women randomly delivered by CS and planned vaginal birth has now been completed and shows that vaginal delivery is safe.3 However, some aspects of twin delivery remain controversial.
Presentation
Twin 1 vertex
Assess the suitability for vaginal delivery allowing for the fact that, even if twin two is cephalic prelabour, it is difficult to predict its eventual presentation at the time of delivery. If the second twin is breech, vaginal delivery is considered safe and is best delivered by assisted breech delivery or breech extraction. If the second twin is tranverse, then delivery can be either with ECV, or internal podalic version and breech extraction.
Twin 1 nonvertex
When twin one is breech, current opinion favours CS. This is the case despite a large, multicentre, retrospective study of breech first births that showed no increased risk attributable to vaginal delivery and in the context that one of the main concerns quoted about vaginal delivery in this situation is the risk of locked twins, the incidence of which is very low at 1/645. The Term Breech Trial was a singleton study and the results should not be extrapolated to twins. However, in the light of these concerns, any decision to proceed with vaginal birth should be made at consultant level. When twin one is transverse, CS is needed.
Intertwin delivery interval
The ideal time interval between the delivery of the first and second twin is not agreed. Undue haste with rupture of the membranes before the presenting part of twin two has entered the pelvis can cause problems, while undue delay is not without hazards too. In one report, umbilical cord arterial and venous pH and base excess were shown to deteriorate with increasing twin-to-twin delivery interval. There were no second twins with an umbilical pH less than 7.00 when delivered within 15 minutes of twin 1. If the intertwin delivery interval was greater than 30 minutes, 27% had an umbilical artery pH of less than 7.00. Among those with an intertwin delivery interval of greater than 30 minutes, 73% had evidence of fetal distress that required operative intervention.
Studies have previously suggested that no specific time interval needs to be set, providing that there is continuous electronic fetal heart rate monitoring of twin 2 and that this is reassuring.
ECV versus internal podalic version for transverse twin two
Both techniques are reasonable, but while many investigators report success with an attempt at ECV in the first instance, other authors have reported lower success rates with ECV with increased maternal complication rates compared with proceeding straight to internal podalic version. Nevertheless, given that ECV is less invasive, it is reasonable to consider this in the first place, if the operator is more comfortable with that technique. The experience of the operator is probably the most important factor, and more senior practitioners may choose to go straight to internal manoeuvres.
Higher multiples
Even though the incidence of triplets is rising, most obstetricians have relatively little experience of delivering triplets and even less of delivering them vaginally. Although a study from the Netherlands reported improved outcome for triplets with vaginal delivery, when compared with CS, the unit was particularly experienced at this type of delivery. For most obstetricians, the safer option would almost certainly be CS.
Previous CS
The scarce evidence available suggests that a trial of labour is a safe option in the absence of a contraindication to vaginal birth. Scar dehiscence rates have been reported to be 0–3%. Clearly, vaginal delivery is most suitable when both twins are longitudinal (both cephalic or cephalic/breech). Employing ECV or internal podalic version for the transverse lie is more controversial.
Preterm/very-low-birthweight twins
There seems to be little difference in outcome between vaginal and caesarean delivery in very-low-birthweight gestations and little difference in terms of perinatal outcome, but fetal monitoring of both twins must be accurate and continuous (see below).
Indications for CS
These include:
conjoined twins
monoamniotic twins
placenta praevia
certain congenital anomalies
possible interlocking twins.
Intrapartum management of vaginal twin delivery
Management of stage 1
In stage 1:
admit to delivery suite
intravenous line
blood tests – full blood count, group and save serum
continuous cardiotocograph on a twin monitor
fetal heart rate abnormalities twin 1 take fetal blood sample
fetal heart rate abnormalities twin 2 perform CS.
If, at any stage, either twin cannot be monitored, then CS may be the only safe option. It is imperative that both twins are monitored and the trace should be scrutinised to ensure that this is the case (i.e. each twin has a distinct rate and both of these are different from the mother’s heart rate). Equally, it is crucial to be sure which twin is which recording, as this has, on occasion, been erroneously interpreted and a fetal blood sample performed on twin 1 for a pathological trace of twin 2.
Ultrasound assessment should be performed by an appropriately trained practitioner to determine:
presentation of each fetus
liquor volume assessment
placental site
viability of each fetus
estimation of fetal weight if not recently performed.
(Ultrasound can also guide the operator if ECV or internal podalic version is needed for twin 2 – see below.)
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
