Medscape Medical News
Jenni Laidman
June 09, 2014
The risk for preterm births nearly tripled when less than 12 months elapsed between pregnancies, according to a study of more than 400,000 births published online June 4 in BJOG.
Emily A. DeFranco, DO, assistant professor, Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children’s Hospital Medical Center, Ohio, and colleagues to analyzed 454,716 birth records of singleton live deliveries at 20 to 44 weeks gestation between 2006 and 2011. The researchers compared gestational age at birth for interpregnancy intervals (IPIs) of less than 12 months, IPIs of 12 to less than 18 months, and IPIs of 18 or more months.
The researchers adjusted for cigarette smoking, maternal age, and race. The adjusted odds ratio (AOR) was 2.78 (95% confidence interval [CI], 2.64 – 2.93) for delivery at less than 39 weeks for an IPI of less than 12 months. More than half of the women in the group with the shortest IPI (53.3%) delivered at fewer than 39 weeks compared with 37.5% of women with IPIs of 18 months or longer (P < .001). Among women with an IPI of less than 12 months, there were fewer births at 40 or more weeks: 16.9% compared with 23.2% for an IPI of 18 months or longer (AOR, 0.67; 95% CI, 0.64 – 0.71).
“Inadequate birth spacing with short interpregnancy intervals is an important risk factor for preterm birth,” the authors write.
Births at 18 months or longer, the “normal” IPI, the authors write, constituted 87.1% of all births to multiparous mothers. Almost 11% of births were with IPIs of 12 to 18 months, and 2.2% had IPIs of less than 12 months. Of all births, 1.1% were at less than 32 weeks and 0.6% were at 20 to 28 weeks.
Seventy-eight percent of the mothers in the study population were white, 19% were black, and 3% were of other races. Short IPI was more frequent in black mothers, as were preterm births. Women with optimal IPI had lower preterm birth rates, although black women had more preterm births even with optimal IPI (11.3% of all optimal IPI births in black women compared with 6.8% in white women; P < .01.)
Shorter IPIs were associated with low education level, limited preterm care, tobacco use, and prior preterm birth. Pregnancy complications such as gestational diabetes, gestational hypertension, and small for gestational age at birth (<10th percentile for gestational age) were also more common with short IPI.
However, the most frequent gestational age for birth was the same in all IPI groups: 39 weeks.
One limitation of the study, the authors write, is that data on pregnancy complications and medical comorbidities are underreported in birth certificate data, making it difficult to adjust for these confounding risk factors.
This work was supported by the Perinatal Institute, Cincinnati Children’s Hospital Medical Center, and March of Dimes. The authors have disclosed no relevant financial relationships.
BJOG. Published online June 4, 2014. Abstract