To examine the association between interpregnancy interval and maternal–neonate health when matching women to their successive pregnancies to control for differences in maternal risk factors and compare these results with traditional unmatched designs.
We conducted a retrospective cohort study of 38,178 women with three or more deliveries (two or greater interpregnancy intervals) between 2000 and 2015 in British Columbia, Canada. We examined interpregnancy interval (0–5, 6–11, 12–17, 18–23 [reference], 24–59, and 60 months or greater) in relation to neonatal outcomes (preterm birth [less than 37 weeks of gestation], small-for-gestational-age birth [less than the 10th centile], use of neonatal intensive care, low birth weight [less than 2,500 g]) and maternal outcomes (gestational diabetes, beginning the subsequent pregnancy obese [body mass index 30 or greater], and preeclampsia–eclampsia). We used conditional logistic regression to compare interpregnancy intervals within the same mother and unconditional (unmatched) logistic regression to enable comparison with prior research.
Analyses using the traditional unmatched design showed significantly increased risks associated with short interpregnancy intervals (eg, there were 232 preterm births [12.8%] in 0–5 months compared with 501 [8.2%] in the 18–23 months reference group; adjusted odds ratio [OR] for preterm birth 1.53, 95% confidence interval [CI] 1.35–1.73). However, these risks were eliminated in within-woman matched analyses (adjusted OR for preterm birth 0.85, 95% CI 0.71–1.02). Matched results indicated that short interpregnancy intervals were significantly associated with increased risk of gestational diabetes (adjusted OR 1.35, 95% CI 1.02–1.80 for 0–5 months) and beginning the subsequent pregnancy obese (adjusted OR 1.61, 95% CI 1.05–2.45 for 0–5 months and adjusted OR 1.43, 95% CI 1.10–1.87 for 6–11 months).
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.
The relationship between intepregnancy interval and adverse neonatal outcomes is confounded, because it largely disappears when using a within-woman matched analysis.Supplemental Digital Content is Available in the Text.
Perinatal Services BC, and the Department of Obstetrics & Gynaecology, University of British Columbia, Vancouver, British Columbia, Canada.
Corresponding author: Gillian E. Hanley, PhD, Diamond Health Care Centre, 6207A 2775 Laurel Street, Vancouver, British Columbia V5Z 1M9, Canada; email: Gillian.email@example.com.
Financial Disclosure The authors did not report any potential conflicts of interest.
Gillian E. Hanley is funded by the Canadian Cancer Society Research Institute and a New Investigator Award from the Canadian Institutes of Health Research. Jennifer A. Hutcheon holds New Investigator Awards from the Canadian Institutes of Health Research and the Michael Smith Foundation for Health Research.
The funders played no role in this study.
Each author has indicated that he or she has met the journal’s requirements for authorship.