This study was presented as an oral presentation at the 2013 Annual Meeting of the Central Association of Obstetricians and Gynecologists, 16–19 October 2013, Napa, CA, USA.
Influence of interpregnancy interval on birth timing
Article first published online: 4 JUN 2014
© 2014 Royal College of Obstetricians and Gynaecologists
BJOG: An International Journal of Obstetrics & Gynaecology
Volume 121, Issue 13, pages 1633–1640, December 2014
How to Cite
Influence of interpregnancy interval on birth timing. BJOG 2014;121:1633–1641., , .
Linked article This article is commented on by Steer P. To view this mini commentary visit http://dx.doi.org/10.1111/14710528.12941.
- Issue published online: 21 NOV 2014
- Article first published online: 4 JUN 2014
- Manuscript Accepted: 17 MAR 2014
- Perinatal Institute
- Cincinnati Children's Hospital Medical Center
- March of Dimes Prematurity Research Center. Grant Number: 22-FY13-543
- Birth spacing;
- birth timing;
- interpregnancy interval;
- preterm birth
To assess the influence of inadequate birth spacing on birth timing distribution across gestation.
Population-based retrospective cohort study using vital statistics birth records.
Singleton, non-anomalous live births ≥20 weeks to multiparous mothers, 2006–2011.
Birth frequency at each gestational week was compared following short IPIs of <6, 6–12 and 12–18 months versus referent group, normal IPI ≥18 months.
Main outcome measures
Frequency of birth at each gestational week; preterm <37 weeks; <39 and ≥40 weeks.
Of 454 716 births, 87% followed a normal IPI ≥18 months, 10.7% had IPI 12–18 months and 2.2% with IPI <12 months. The risk of delivery <39 weeks was higher following short IPI <12 months, adjOR (odds ratio) 2.78 (95% CI 2.64, 2.93). 53.3% of women delivered before the 39th week after IPI <12 months compared with 37.5% of women with normal IPI, P < 0.001. Likewise, birth at ≥40 weeks was decreased (16.9%) following short IPI <12 months compared to normal IPI, 23.2%, adjOR 0.67 (95% CI 0.64, 0.71). This resulted in a shift of the frequency distribution curve of birth by week of gestation to the left for pregnancies following a short IPI <12 months and 12–18 months compared to, birth spacing ≥18 months.
While short IPI is a known risk factor for preterm birth, our data show that inadequate birth spacing is associated with decreased gestational age for all births. Pregnancies following short IPIs have a higher frequency of birth at all weeks of gestation prior to 39 and fewer births ≥40 weeks, resulting in overall shortened pregnancy duration.