Sunanda is exhilarated and at the same time nervous. She has had an ultrasound scan and discovered she is having twins! When she saw the two little babies inside her, her heart skipped a beat and then started racing. Her husband too is thrilled at this unexpected bonus! 

Sheela and her husband have been trying for a pregnancy for a few years. They had undergone treatment with medications and have now conceived after a fertility procedure. She had her pregnancy confirmed after an ultrasound scan. She too is having twins.

How common is a twin pregnancy? 

The chance of having identical twins i.e. twins from a single egg, has remained fairly constant throughout the world. One out of 250 women will have identical twins. However, the rate of having non-identical twins or fraternal twins i.e. twins formed from two different eggs is increasing all over.  

The advent of IVF (in vitro fertilisation or ‘test tube baby’) has also contributed to the increased rate of twins. This procedure typically involves implanting more than one embryo in the uterus and, therefore, is more likely to result in twins, triplets, quadruplets or more.

How are twins formed?

There are two different kinds of twins: 

Identical twins

Are rarer and are derived from a single fertilised egg. Identical twins may share a placenta, but each baby usually has its own amniotic sac. The twins will have identical genes and be of the same sex, have the same blood type, hair colour and eye colour, and are difficult to differentiate in appearance.

Non-identical twins or fraternal twins

Are derived from two fertilised eggs released during the same menstrual cycle. These twins will have genetic differences in the same way as normal brothers and sisters. They may or may not be of the same sex.