Shabina Akhtar explains: The bringing forth of multiple offspring at the time of birth is commonly termed multiple birth. Twins are the most common type of multiple birth in humans. But cases of triplets, quadruplets and septuplets have also been recorded.

“Multiple ovulation (releasing more than one ovum) during single menstrual cycle and their consequent fertilisation lead to the development of multiple foetus during a single pregnancy,” said Dr Baidyanath Chakravarty, consultant gynaecologist, Institute of Reproductive Medicine, Calcutta.

During each menstrual cycle, only one egg matures among 30 eggs that are competing for maturity. The fertilisation of this single ovum, followed by the segmentation of the blastocyst (modified blastula of a placental mammal), leads to the development of uniovular twins or identical twins.

But at times two or three eggs may also mature in a single menstrual month. The fertilisation of the multiple eggs released leads to the development of the binovular twins. “When these two fertilised eggs segment into two parts respectively, then quadruplets are formed,” said Dr Chakravarty. Natural ovulation doesn’t favour multiple birth.

The use of fertility drugs to stimulate ovulation, or assisted reproductive technology (ART), which transfers multiple embryos to the womb (such as in vitro fertilisation, or IVF), greatly increases the chance of multiple pregnancy, he added.

The question was sent by Sumon Datta, Hind Motors