Giving birth to a second child less than 18 months after having a first reduces the gestational age at birth of the subsequent children, according to study results published in BJOG: An International Journal of Obstetrics and Gynaecology.
Short intervals between pregnancies increased the likelihood of delivery the second baby prior to 39 weeks.
The population-based study relied on birth records from the Ohio Department of Health and included 454,716 live births from women with two or more pregnancies. For the study, short interpregnancy interval was divided into two groups: women who waited less than a year from giving birth to conceiving a second child and those who became pregnant within 12 to 18 months of giving birth. Those groups were compared with women who were considered to have an optimal interpregnancy interval of 18 months or more.
- Women who conceive a child less than 18 months after giving birth are more likely to deliver the subsequent child prior to 39 weeks.
- A shorter interval between pregnancies is associated not only with preterm deliveries but also with a reduction in the overall length of pregnancy.
Results showed that women who waited less than 18 months were more likely to give birth prior to 39 weeks’ gestation when compared with women who had optimal birth spacing. Among women who became pregnant again within a year, 53.3% delivered before 39 weeks, compared with 37.5% of women who became pregnant after 18 months.
In addition, the rate of preterm birth before 37 weeks’ gestation was higher in women who conceived within a year after giving birth. These women were more than twice as likely to give birth before 37 weeks compared with those who had 18 months are longer between last delivery and conception (20.1% vs 7.7%, respectively), the study authors reported.
"Short interpregnancy interval is a known risk factor for preterm birth. However, this new research shows that inadequate birth spacing is associated with shorter overall pregnancy duration,” explained Emily DeFranco, DO, Assistant Professor of Maternal-Fetal Medicine at the University of Cincinnati College of Medicine in Ohio and the Center for Prevention of Preterm Birth at Cincinnati Children's Hospital Medical Center, and coauthor of the study, in a news release. "This study has potential clinical impact on reducing the overall rate of preterm birth across the world through counselling [sic] women on the importance of adequate birth spacing, especially focusing on women known to be at inherently high risk for preterm birth."