Around a dozen triplets and some 850 pairs of twins are born in Finland each year. In the 1990s the number of triplets born was as much three times higher.

In the late 1990s, specialists began changing their practices after realising the link between multiple births and in vitro fertilisation. Moms of multiples face higher risks during pregnancy, and multiple pregnancies also carry an increased risk for babies. Half of all twins are born premature, and the risk of cerebral palsy in multiple fetus pregnancies is many times that of single births, according to fertility professor Aila Tiitinen.

“We began developing fertility treatments that aimed for single births,” says Tiitinen.

Today, only one embryo is usually transferred into the woman’s uterus. Other embryos can be frozen and transferred later if necessary. Embryo freezing, or cryopreservation, has significantly developed since the 1990s, when multiple embryos were placed into the uterus as a rule.

Meanwhile, naturally occurring multiples are becoming more common as the average age of mothers continues to rise.