Preterm births are more significant in twin pregnancies than in singletons

By: Dr. Shelly Singh, Senior Consultant, Obstetrics and Gynaecology, Rosewalk Hospital

There is an increased number of twin pregnancies and higher order births owing to more cases of pregnancies due to artificial reproductive technology (ART) or IVF. Even liberal use of ovulation inducing medicines leads to a greater incidence of twin and higher order pregnancies. There are specific challenges to twin pregnancies; one of the commonest being preterm births.

How common are preterm births in twin pregnancies?
About 50 % of twin pregnancies end in preterm births before 36 weeks (a month before the 40 weeks of singleton pregnancies). Some studies have shown that preterm deliveries at <37 weeks are 5.7 times more and at <32 weeks 7.1 times more in twin pregnancies compared to singleton pregnancies . Twin gestations of 36 weeks are equivalent to 40 weeks singleton pregnancies. The reasons for preterm deliveries in twin pregnancies are many.

The first could be due to early delivery which is needed medically due to associated complications of twin pregnancies called Iatrogenic preterm deliveries; the other is due to overdistension of the uterus which is part and parcel of bearing two babies , sometimes with a large placenta and excessive amniotic fluid around the babies . This could lead to spontaneous preterm labour or due to PROM (preterm rupture of membranes)

Let’s delve into both these reasons
One of the common problems in twin gestation is Preeclampsia.
Preeclampsia is defined as high blood pressure after 20 weeks of pregnancy accompanied by swelling of the body and protein in the urine. Preeclampsia causes severe risks to the pregnant lady. These include throwing fits (eclampsia) , clots in the brain , liver derangements , bleeding disorders due to low platelets and breathing disorders due to lung issues .

There can also be premature separation of the placenta from the uterus causing ominous bleeding both concealed in the uterus and revealed. Even intrauterine deaths of babies are a known complication due to this condition called abruption placentae. This preeclampsia may warrant preterm delivery due to the above mentioned complications.

Placental problems
Twin pregnancies may be associated with a single placenta or two separate placentas depending on the type of twin gestation. The placenta is attached to the uterine wall and supplies oxygen and nutrients to the babies. A large placenta may be low lying in the uterus (placenta previa) which can bleed at any time, sometimes prematurely, causing the need to do an urgent preterm delivery.

Abruption, as mentioned above, also leads to bleeding – internally inside the uterus or externally, warranting a preterm delivery to save the lives of the mother and babies. Another condition in single shared placentas with shared circulation between twins is called TTTS or Twin to twin transfusion syndrome which may sometimes require a preterm delivery if it compromises the babies.

Premature rupture of membranes (PROM)
Twin babies are enveloped in sacs of liquor called amniotic fluid. In twin gestation, due to overdistension of the uterus, there may be a preterm leaking of amniotic fluid due to breaking of this “ water bag”. This is far more common in twin gestation compared to singleton pregnancies. PROM can lead to infection and also precipitate preterm labour. This is one of the reasons why preterm deliveries are commoner in twin pregnancies.

Fetal growth restriction
Preterm babies are generally smaller than singleton ones. These babies are small or do not fulfill their full potential for growth inside the uterus due to numerous factors. Some twins may be selectively fetal growth restricted which means one baby is significantly smaller than the other due to shared unequal circulation etc. If these babies do not grow adequately in the womb early delivery may be needed.

Hence, whatever be the reason – medically induced or spontaneous, preterm deliveries are more common in twins and come with their own set of problems post birth. Whenever diagnosed with twin gestation it is a good idea to discuss all the issues which come with the little ones Remember: “Two babies twice the fun, Though many times, preterm ones.”