Interpregnancy Interval and Adverse Pregnancy Outcomes

Abstract

Previously reported associations between short interpregnancy intervals and adverse neonatal outcomes may not be causal. However, short interpregnancy interval is associated with increased risk of gestational diabetes and beginning a subsequent pregnancy obese.

Within-Family Analysis of Interpregnancy Interval and Adverse Birth Outcomes

“…However, with our more rigorous control of unmeasured confounding factors in sibling-, cousin-, and post-birth interval analyses, our interpretation is different from the causal assumptions made by previous studies. Our findings are in agreement with recent research showing that sibling-comparisons attenuate the association between short interpregnancy intervals and adverse birth outcomes (15, 16). Our findings are also in agreement with another paper that used post-birth interpregnancy intervals (14).…”

“…Further, the lack of association between long post-birth interpregnancy interval and adverse birth outcomes indicates that within-family confounding for long interpregnancy interval is minimal, and there is no indication of an earlier-born's birth outcome influencing the odds of future long interpregnancy intervals. This supports and extends previous sibling-comparison studies showing elevated risk for SGA (15) and LBW (16) following long-interpregnancy interval by introducing results from cousin- and post-birth interval analyses. A large meta-analysis (1) has also previously shown increased risk for PTB, LBW, and SGA following a long interpregnancy interval.…”

“…Our findings are also in agreement with another paper that used post-birth interpregnancy intervals (14). In addition, one study also found that the directionality of association switches for LBW in the sibling-comparison model (16) which may suggest a suppression effect.…”

“…Post-birth intervals were calculated between the birth of the second-born and the conception of the third-born sibling and used to predict second-born outcomes. Interpregnancy intervals were categorized as 0 to 5 months, 6 to 11 months, 12 to 17 months, 18 to 23 months (referent), 24 to 59 months, and 60 or more months in order to allow for comparison across previous studies (15, 16). …”

“…Cousin-and sibling-comparison designs rule out influence from unmeasured environmental and genetic risks that make relatives similar (24). Previous research has used sibling-comparison designs to investigate these associations (15, 16). We sought to replicate those findings here; we also include a cousin-comparison.…”