“Nobody in my family or my husband’s family has twins, but two years after my first son was born, I conceived a boy and a girl. The doctor left us alone for a few minutes, but when she returned, we were still looking at each other in complete silence, as we processed the news that caused us to feel fright and delight all at once,” says Dubai resident and cake craft artist Khushi Malani, 40, mum to Aryan, 13, and twins Rhea and Rehan, 10.
The Malanis, it seems, are something of the rule rather than the exception in the 21st century, as a study conducted by the University of Oxford and published in the Human Reproduction journal reported on Saturday.
Researchers, led by professor Christiaan Monden, found that more than 1.6 million twins are being born every year, which works out to one in 42 children. This figure is nearly a third more than those reported in the 1980s – when it was 9 in every 1,000 compared with 12 in every 1,000.
The main reason cited is the rising use of IVF and other fertility treatments, which are sought by parents who may be unable to conceive owing to age or lifestyle-related issues. Somewhat paradoxically, the team noted that with fertility clinics better able to modify their techniques and technologies, the rate of twin births may now be at its peak.
The increase is most notable in fraternal or non-identical twins, as the rate of identical twins has not changed drastically.
Prof Monden and his team drew their conclusions on the back of data gathered from 1980 to 2015, from 165 countries.
Why does IVF lead to twins?
Medically-assisted reproduction is more common than ever before, and takes forms such as in vitro fertilisation (IVF), ovarian stimulation and artificial insemination. These techniques are linked to a likelihood of multiple births compared with natural conception because they often involve women taking hormones to stimulate egg production.
This may lead to the release of two eggs at the same time.
IVF clinics also tend to transfer more than one embryo to boost the chances of conception, which leads to a higher occurrence of twins, triplets or even quadruplets.
Older women more likely to have twins?
Delayed childbirth is another contributing factor to many women conceiving twins, albeit to a lesser extent than fertility treatments.
Couples often wait it out to become more financially independent and more women are joining the workforce, especially in high-income and middle-income countries, and so delay starting families.
As older women are more likely to release two eggs at the same time, there is a chance that they will conceive twins.
Modern technology to the rescue
On the one hand, modern medicine is able to ensure that the mortality rate among twins born today is lower compared with the 1970s and 1980s, which means "more twin pairs than ever before will survive until adulthood", according to the study.
On the other hand, twins are still considered a high-risk group "associated with complications during pregnancy, at birth and thereafter, including preterm deliveries, lower birth weight, increased stillbirths and infant and maternal mortality", compared with single births.
Accordingly, IVF clinics in many countries have been directed to rely on new medical technologies, and reduce the number of transferred embryos and focus on “successful live birth delivery of singletons”, says the study, which predicts that twin births may in fact start to plateau in the months and years ahead.