Does less time between pregnancies lead to more preterm births?

Women with interpregnancy intervals (IPIs) of less than 18 months may be at increased risk of preterm delivery, according to a new study in BJOG.

Researchers from the University of Cincinnati College of Medicine and Cincinnati Children’s Hospital Medical Center used Ohio Department of Health records to identify singleton, non-anomalous live births ≥20 week to multiparous mothers that had occurred from 2006 to 2011. The recorded 454,716 births were grouped into IPIs of <6 months, 6 to 12 months, 12 to 18 months, and ≥18 months for comparison.

The vast majority (87%) of the deliveries followed a normal IPI ≥18 months; 10.7% had an IPI of 12 to 18 months; and 2.2% had an IPI of <12 months. A short IPI (<12 months) had a higher risk of delivery <39 weeks (adjusted odds ratio [_adjOR] 2.78, 95% confidence interval [CI] 2.64, 2.93). Of the women with an IPI of <12 weeks, 53.3% delivered before their pregnancy entered 39 weeks; 37.5% of women with a normal IPI delivered before the 39^th week, P<0.001. The rate of delivery at ≥40 weeks following an IPI of <12 months was smaller in comparison to a normal IPI (23.2% _adjOR 0.67, 95% CI, 0.64, 0.71). The result was a  shift to the left in the frequency distribution curve of delivery  for pregnancies when the IPI was <12 months or 12 to 18 months, compared with an IPI of ≥18 months.

The investigators concluded that the data show a short IPI is associated with decreased gestational age for all births. According to their research, women with short IPIs have a higher frequency of birth in all weeks prior to 39 and fewer births at or after 40 weeks.

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