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Subfecundity and neonatal mortality: longitudinal study within the Danish national birth cohort

Treatment for infertility correlates with adverse outcomes in pregnancy, especially in singleton deliveries.1 A long time to pregnancy (subfecundity) also correlates with adverse outcomes,2–4 but few studies evaluating treatment take subfecundity into consideration. We explored the association between time to pregnancy and neonatal death in the Danish national birth cohort.

We identified 27 624 firstborn singleton babies, born alive from the 24th week of gestation between March 1998 and December 2001, whose mothers were enrolled in the Danish national birth cohort.4 5 Mothers had been interviewed during pregnancy (50% by the 16th completed week and 95% by the 25th) and asked about pregnancy planning and other factors.

Women who reported having planned or partly planned their pregnancy were asked how long it had taken them to conceive. If the answer was six months or longer, they were further asked whether they had received infertility treatment. We excluded 402 women reporting infertility treatment after …