Twins become parents later than single-birth children and bring fewer children into the world, a new Linköping University study shows.
The study of the registers covered all children born between 1973 and 1983 – a million in total, of which 16,500 were twins. It confirms the estimation that twins, more often than single births, are born too early (34 % against 4 %) and with low birth weight (35-40 % against 3 %), a consequence of such things as a higher share of Caesarian sections.
But what this study also shows is that twins, when they reach adulthood, have fewer children than average. This is also valid when comparing them to premature single births.
“Both male and female twins have a 10 % less chance of having their own children compared with single-birth children who have the same birth characteristics,” says Marie Bladh, statistician and PhD student in Obstetrics and Gynaecology.
Along with her supervisor Gunilla Sydsjö, professor of Reproductive Health Research at Linköping University, she will publish her results in the scientific journal BMC Pregnancy and Childbirth.
The causes can be social. It has long been known that women who give birth to twins are more highly educated than the average new mother. This could be a reason why they put off having children; the older they are, the more likely the probability of having twins.
“It’s likely that their children have a ‘social inheritance’ that more often leads them to choose to pursue their studies further. Another reason could be that they wait to find a partner because they already have a ‘psychological’ partner in their twin sibling,” Bladh says.
But it is also probable that as-yet unknown medical factors lie behind the phenomenon.
“We’re now delving further into the health of the mothers during pregnancy: nutrition indicators, infections, and so on that can influence their twins’ ability to have children themselves,” Sydsjö says.
In her role as a therapist at the University Hospital Women’s Clinic, she has broad experience in helping and treating childless couples.
“We see an increasing share of parents seeking fertility treatments. Through these studies, we can learn more about reasons for childlessness,” Sydsjö says.
The share of twin births is now around 1 % – approximately 1,000 of a total of 110,000 per year. During the so-called “twin boom” at the turn of the millennium the share was about 1.6 %, which was a result of in vitro fertilisation (IVF) becoming routine in hospitals. Nearly one-fourth of these children were born as twins, owing to the fact that two fertilised eggs were often put back into the mother’s uterus.
Source: Linkoping University