Gab Kovacs1 and Paula Briggs2
(1)
Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
(2)
Sexual and Reproductive Health, Southport and Ormskirk Hospital, Southport, UK
Definition
Incidence
Aetiology and Pathogenesis
Clinical Assessment
History
Examination
Investigations
Treatment
Antenatal
Surgical
Delivery
Prognosis
Definition
Multiple pregnancy is when there is more than one foetus. Two babies are twins, three babies are triplets, four babies are quadruplets and five babies are quintuplets and so on.
Twins can be mono-zygotic (MZ) (from one zygote – where an embryo splits) or di-zygotic (DZ) where they arise from two different fertilised oocytes. They can be mono-chorionic or di-chorionic. Chorionicity is critical for management. Mono-chorionic twins are always mono-zygotic.
Chorionicity is determined by ultrasound in the first trimester. Mono-chorionic twins need much closer surveillance. Most mono-chorionic twins are di-amniotic, each with its own amniotic sac, but occasionally they are mono-amniotic.
Incidence
The incidence of natural twins is 1:90, triplets is 1:90 × 90 = 1:8,100, and quads 1:90 × 90 × 90 = 1:729,000.
During the last few decades the incidence of multiple pregnancies has risen as a result of reproductive technology, ovulation induction and in vitro fertilization.
Aetiology and Pathogenesis
Di-zygotic twins occur as a result of superovulation, but can also be due to the transfer of multiple embryos, resulting in non-identical twins. Monozygotic twins are due to the embryo splitting. It is suggested that embryos transferred during IVF at the blastocyst stage have a higher incidence of monozygotic twinning (incidence 2 %).
Whether twins are mono-amniotic or bi-amniotic, mono-chorionic or bi-chorionic depends on the gestation at which the embryo splits.
Clinical Assessment
History
Multiple pregnancy is suspected if the woman complains of excessive morning sickness or a bigger “bump” than expected.
Examination
In early pregnancy, a uterus larger than dates is the first hint of a multiple pregnancy. Beyond 28 weeks, a multiple pregnancy may be suspected when more than two poles can be palpated.
Investigations
· Biochemistry – during the early first trimester, the level of quantitative beta HCG may be higher than expected for the stage of gestation.
· Ultrasound – the definitive test is ultrasound examination. It is also essential to in order to determine chorionicity.
Treatment
Antenatal
A twin pregnancy is considered “high risk” due to maternal and foetal factors.
The treatment of di-chorionic twins is not significantly different to a singleton pregnancy. The complications of preterm birth, APH, PPH, maternal hypertension, and the risk of congenital abnormality of the foetuses, is greater. Consequently, more frequent antenatal visits are required.
Women with mono-chorionic twins should have ultrasound surveillance for twin-to-twin-transfusion syndrome (TTTS) (which occurs in about ten per cent of monochorionic twins), and intrauterine growth restriction (IUGR) from the start of the second trimester. This includes assessing each twin for growth, amniotic fluid volume, bladder volume, and umbilical and middle cerebral artery doppler wave form.
Twin anemia/polycythemia syndrome (TAPS) occurs in 5 % of monochorionic twins, and is the result of a slow blood transfusion from the donor to recipient. As there is no discordance in amniotic fluid, this is diagnosed by measuring peak middle cerebral artery blood flow on ultrasound.
Surgical
The possibility of “foetal reduction” should be considered for high multiples (triplets or greater). This is performed by injecting, under ultrasound control, the smallest of the fetuses with intra-cardiac potassium chloride, which causes cardiac arrest. The risk is that the other fetuses may also succumb.
If there is TTTS, laser ablation of vascular connections between the placentas should be considered.
It is also recommended that mono-chorionic twins be delivered at 37 weeks because of a higher rate of sudden still birth.
Delivery
Mode of Delivery
Many twin pregnancies are delivered by Caesarean Section. Nevertheless, the principles of how to deliver twins should be understood.
Vaginal Delivery
Vaginal delivery should be undertaken in a setting where emergency CS can be undertaken at short notice. Both twins should be monitored with CTG. Anaesthetic backup should be available to provide adequate analgesia for the second stage of vaginal delivery. Having an epidural is advisable as this facilitates assisted delivery of the second twin.
Having the first twin present as a breech is a relative contra-indication to vaginal delivery.
The delivery of the first twin should be treated on its merits.
After delivery of the first twin, any syntocinon infusion should be stopped. It should be ascertained that the second twin is longitudinal, at which stage the syntocinon is recommenced, and the membranes are ruptured. If the second twin is cephalic either the mother can push, or an assisted delivery with vacuum or forceps can be carried out. If the second twin is breech, assisted breech delivery/or breech extraction should be carried out. If the lie of the second twin is not longitudinal, internal version and breech extraction should be undertaken. This is facilitated by the use of an epidural.
After delivery, the third stage should be managed actively, because of the risk PPH. The use of an oxytocic infusion post delivery is helpful in decreasing the risk of PPH.
Prognosis
In a study of over 700 twin pregnancies, it was observed that about one in four diagnosed on an early ultrasound, spontaneously reduced to a singleton pregnancy. Whilst 6.6 % of women lost both twins, one in five went on to term (>37 weeks), whilst one in three delivered early between 33 and 36 weeks. Furthermore 20 % delivered before 33 weeks.
The perinatal mortality per 1,000 births was 6.5 for babies delivered over 37 weeks, 8.0 for babies delivered between 33 and 36 weeks, and 41.7 for babies delivered between 29 and 32 weeks, and 500 (one in two) for babies born under 28 weeks.
Spontaneous triplets are rare, and most are the result of ART. Consequently they almost always result from three different embryos.
Their management is similar to twins, but delivery is always by Caesarean Section.