Objective: To study whether interpregnancy interval is associated with increased risks of stillbirth and early neonatal death and whether this possible association is confounded by maternal characteristics and previous reproductive history.
Methods: In a Swedish nationwide study of 410,021 women's first and second singleton deliveries between 1983 and 1997, we investigated the influence of interpregnancy interval on the subsequent risks of stillbirth and early neonatal death. Odds ratios (ORs) with 95% confidence intervals (CIs) estimated using unconditional logistic regression were adjusted for maternal characteristics and previous pregnancy outcome categorized into stillbirth, early neonatal death, preterm, or small for gestational age delivery.
Results: Compared with interpregnancy intervals between 12 and 35 months, very short interpregnancy intervals (0-3 months) were, in the univariate analyses, associated with increased risks of stillbirth and early neonatal death (crude OR 1.9; 95% CI 1.3, 2.7; and 1.8; 1.2, 2.8, respectively). However, after adjusting for maternal characteristics and previous reproductive history, women with interpregnancy intervals of 0 to 3 months were not at increased risks of stillbirth (adjusted OR 1.3; 95% CI 0.8, 2.1) or early neonatal death (adjusted OR 0.9; 95% CI 0.5, 1.6). Women with interpregnancy intervals of 72 months and longer were at increased risk of stillbirth (adjusted OR 1.5; 95% CI 1.1, 2.1) and possibly early neonatal death (adjusted OR 1.3; 95% CI 0.9, 2.1).
Conclusion: Short interpregnancy intervals appear not to be causally associated with increased risk of stillbirth and early neonatal death, whereas long interpregnancy intervals were associated with increased risk of stillbirth and possibly early neonatal death.