Infertility twins born earlier, but not dangerously so

Twins resulting from subfertility treatment are born about 4 days sooner (95% CI; 2.7–5.2) and are about 60% more likely (OR 1.6; 1.4–1.8) to be born slightly preterm (between 34 and 36 weeks) when compared with naturally conceived twins, according to the results of a population-based cohort study from Belgium. But the differences are largely explained by a first birth effect among subfertile couples and are mitigated by the protective effect of dizygotic twinning; most twins resulting from subfertility treatment are dizygotic.

To obtain the findings, researchers looked at 2,915 spontaneous twins, 710 twins born after ovarian stimulation, and 743 twins born after in vitro fertilization or intracytoplasmic sperm injection.

While the study lacked data on potential confounding by socioeconomic status, it is the first population-based twin study to look at the relationship between subfertility treatment (rather than reproductive technologies) and gestational length.