Interpregnancy interval and risk of stillbirth: a population-based case control study

We examined the association between interpregnancy intervals (IPIs) and stillbirth (defined as fetal death ≥20 weeks), as both short and long IPIs have been associated with adverse perinatal outcomes. Prior pregnancy loss is also a known risk factor for stillbirth, and women who suffer a prior loss often have shorter IPIs. For these reasons, we also sought to quantify the proportion of the association between prior pregnancy loss and subsequent stillbirth risk that may be attributed to a short IPI.

We used data from the Stillbirth Collaborative Research Network, a multisite case-control study conducted in 2006-2008, restricted to singleton pregnancies among multiparous or multigravid women (985 controls and 291 cases). We accounted for complex sample design and nonparticipation with weighted multivariable logistic regression.

In the adjusted models, IPIs <6 months, as compared with a reference of 18-23 months, were associated with increased odds of stillbirth (aOR 1.6, 95% CI: 0.8, 3.4). Long IPIs (60-100 months) were also associated with an increased odds of stillbirth (aOR 2.4, 95% CI: 1.2, 4.5). After control for covariates, about one-fifth (21.2%) of the association of prior pregnancy loss (stillbirth, ectopic pregnancy, molar pregnancy, or spontaneous abortion) and stillbirth may be attributable to a short IPI.

Our results suggest that women who experience a prior pregnancy loss may benefit from additional counseling on adequate birth spacing to reduce subsequent stillbirth risk.