30+ women more likely to have multiple conception


2 Feb 2009, 0230 hrs IST


How do multiple births of twins or octuplets occur?


Unlike most mammals, human beings are biologically designed to have one child per pregnancy. The female body releases one egg per month, which when fertilized by one sperm forms a zygote that later develops into a fetus and finally a baby. However, in exceptional cases, a single pregnancy can result in more than one baby. There are two common types of multiple births fraternal (dizygotic) and identical (monozygotic). If the female body releases more than one egg and all get fertilized during conception, the resultant babies are fraternal siblings. When the zygote of one fertilized egg splits into more than one embryo, it results in identical siblings. Thus, identical siblings have the same genetic material, while fraternal siblings are like normal siblings. Identical twinning results in all boys or all girls, while a fraternal twinning could be one boy and one girl. Polyzygotic births can have both fraternal and identical siblings.

What are the factors that increase chances of multiple pregnancy?

Women over 30 have greater chances of multiple conception. Family history also contributes. A woman who has already had one or more pregnancies is also more likely to have multiple babies. In the US, African-American women have been found more likely to have twins than any other race. Asian and native Americans have the lowest twinning rates, while Caucasian women, especially those over 35 years of age, have the highest rate of higher-order multiple births (triplets or more). Apart from natural causes, in-vitro fertilization can also help in conceiving more than one baby in a single pregnancy. One of the major complications related to IVF is the risk of multiple births. In common practice, multiple embryos are transferred into the mother's body to increase the conception probability, which can result in multiple births. In a few countries like the UK, there is a strict limit on the number of embryos that may be transferred to the mother's body. The US does not have such a law, but according to the guidelines of American Society for Reproductive Medicine implanting of more than two embryos is generally prohibited.

Why are multiple births a cause for concern?

Apart from being highly susceptible to anaemia, women with multiple fetuses are more likely to develop high blood pressure, which increases the chance of early detachment of the placenta. Multiple fetuses mean multiple placenta and hence multiple bleeding sites increasing the risk of post-natal haemorrhage. About 50% of twins and nearly all higher-order multiple births are premature births. Premature babies have a tough time surviving outside the mother's body. Because of the complications, doctors often advise multi-fetal pregnancy reduction, in which one or more fetuses are killed by lethal medication.

What are the social concerns about multiple births?

In the case of the mother of the LA octuplets, the social aspects of multiple pregnancy are also being debated. It's difficult for the mother to breastfeed all the babies, which can deprive them of essential nutrition. Simple things like changing nappies can turn the children's infant days into more than a full-time job for the mother because she will have to change something like 64 nappies per day.