Influence of interpregnancy interval on birth timing

Authors

  • EA DeFranco,

    Corresponding author
    1. Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
    2. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
    • Correspondence: EA DeFranco, Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine, Medical Sciences Building, Room 5464, 231 Albert Sabin Way, Cincinnati, OH 45267-0526, USA. Email emily.defranco@uc.edu

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  • S Ehrlich,

    1. Division of Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
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  • LJ Muglia

    1. Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
    2. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine, Cincinnati, OH, USA
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  • 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.
  • Linked article This article is commented on by Steer P. To view this mini commentary visit http://dx.doi.org/10.1111/14710528.12941.

Abstract

Objective

To assess the influence of inadequate birth spacing on birth timing distribution across gestation.

Design

Population-based retrospective cohort study using vital statistics birth records.

Setting

Ohio, USA.

Study Population

Singleton, non-anomalous live births ≥20 weeks to multiparous mothers, 2006–2011.

Methods

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.

Results

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,< 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.

Conclusions

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.

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