As a general rule, babies born during gestational weeks 39 and 40 (full term) get the very healthiest starts in life. Those born before week 39 and after week 40 are more likely to face difficulties. A recent study indicates pregnancies grow shorter if there is an interval shorter than 18 months between pregnancies. This finding suggests a mixed blessing, depending on how far along a pregnancy is when childbirth occurs.

Pregnant belly with handsEmily DeFranco is a co-author of the report of the study. She is an assistant professor of maternal-fetal medicine at the University of Cincinnati (Ohio) College of Medicine and is affiliated with the Center for Prevention of Preterm Birth, a branch of the Cincinnati Children’s Hospital Medical Center. The focus of her study was the influence of short interpregnancy intervals (IPIs) on the health of the baby.

DeFranco and her research team examined the medical records of 454,716 singletons born without complication to mothers who had two or more children during a six-year period. The mothers were categorized according to the length of IPI:

  • Less than 12 months between pregnancies
  • 12 to 18 months between
  • 18 months or more between pregnancies

“Short interpregnancy interval is a known risk factor for preterm birth,” according to DeFranco. When children are born prematurely, they are at higher risk of feeding and sensory problems and their risk for cerebral palsy is high. The US Centers for Disease Control and Prevention (CDC) defines preterm birth as occurring before week 37 but many maternal-fetal specialists report better neonatal outcomes when childbirth occurs after the 39-week mark. The CDC advises scheduled deliveries to occur after week 39.

The DeFranco study found the shortest IPIs were more likely to result in shorter pregnancies. When pregnancies were less than a year apart, the second pregnancy was 53.3% more likely to end before week 39. Babies born less than a year after their mother’s previous pregnancy were at twice the risk for premature delivery (before week 37).

The rate of premature delivery dropped to just 37.5% when there was a year or more between pregnancies.

There is evidence some babies benefited from short intervals between pregnancies. When there were fewer than 12 months between pregnancies, the number of pregnancies lasting beyond week 40 was 17% lower than expected. Some complications of post-term delivery include decreased amniotic fluid, compression of the umbilical cord that could cause oxygen deprivation, release of meconium in the womb, pneumonia caused by inhalation of the meconium, and babies too large to pass through the birth canal.

Source: DeFranco, EA, et al. “Influence of interpregnancy interval on birth timing.” BJOG. John Wiley & Sons, Inc. Jun 4, 2014. Web. Jun 16, 2014.

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