Perinatal outcomes in singletons after fresh IVF/ICSI – a cohort study comparing the Bern IVF Cohort with a tertiary center cohort and the national live birth registry

How are perinatal outcomes of live-born singletons after stimulated and unstimulated IVF different from perinatal outcomes in (i) children born in a tertiary centre and (ii) all children born in Switzerland?This cohort study compared the perinatal outcomes of two birth cohorts and the national live birth registry. Relative risks were calculated using modified Poisson regression and clustering for siblings and adjustment for maternal age, parity and childs sex.Of the 636,639 live births, 311 were in the Bern IVF Cohort (144 stimulated, 167 unstimulated), 2332 in the tertiary centre and 633,996 in the Swiss Live Birth Registry (SLBR). Perinatal outcomes following IVF did not differ compared with births in the SLBR (adjusted relative risk [aRR]; 95% confidence interval [CI]), with the exception of the increased risk of small for gestational age (1.31; 1.01 to 1.70, P = 0.04; aRR 1.12; 0.87 to 1.45, P = 0.39). Children born following stimulated IVF had a higher risk of low birthweight (2.17; 1.27 to 3.69, P < 0.01; aRR 1.72; 1.01 to 2.93, P = 0.05), and of being small for gestational age (1.50; 1.05 to 2.14, P = 0.03; aRR 1.31; 0.92 to 1.87; P = 0.13), whereas children born after unstimulated IVF had no increased risks compared with the SLBR. Higher Caesarean rate after IVF was mainly associated with higher maternal age.Singletons in the Bern IVF Cohort do not show less favourable perinatal outcomes. Gonadotrophin stimulation seems to have an effect, because lower risks were associated with unstimulated IVF.