Short interpregnancy interval is associated with increased risks to the mother and fetusBMJ 2018; 363 doi: https://doi.org/10.1136/bmj.k4536 (Published 29 October 2018) Cite this as: BMJ 2018;363:k4536
A gap of less than a year between giving birth and conceiving another child is associated with increased risks for women of all ages, according to a large cohort study.1
A short interpregnancy interval was associated with risks to the fetus and infant, although to a greater extent for younger women (aged 20 to 34 years) than for women 35 years or older. For older women, an interpregnancy interval under 12 months was associated with a significant increased risk of maternal death or severe morbidity such as blood transfusion, admission to intensive care, or organ failure.
The study, published in JAMA Internal Medicine, included 148 544 pregnancies recorded in the British Columbia Perinatal Data Registry over a 10 year period. Among women aged 35 years or older, the risk of maternal mortality or severe morbidity was 0.62% for a six month interpregnancy interval compared with 0.26% at 18 months (adjusted risk ratio 2.39; 95% CI, 2.03 to 2.80). For women aged 20 to 34 there were no increased risks of maternal mortality or severe morbidity with a short interpregnancy interval.
The researchers calculated a fetal and infant composite outcome measure which included stillbirth, infant death within one year, birthweight below the 10th percentile, and delivery before 28 weeks. The risks of adverse fetal and infant outcomes were more pronounced for women aged 20 to 34 years (2.0% at 6 months compared with 1.4% at 18 months; adjusted risk ratio 1.42; 95% CI, 1.36 to 1.47) than for older women (2.1% at 6 months v 1.8% at 8 months; adjusted risk ratio 1.15; 95% CI, 1.01 to 1.31). The risk of spontaneous preterm delivery was also higher with a short interpregnancy interval for women of all ages.
Most previous studies looking at short interpregnancy interval only included women who continued the pregnancy to delivery but this study included women who had terminations, whether spontaneous or induced, before 20 weeks gestation. This is important as in older women such terminations are often related to foetal abnormalities or maternal comorbidities.
In an accompanying editorial, Stephanie Teal and Jeanelle Sheeder from the University of Colorado School of Medicine, Aurora, United States, wrote: “This evidence appears to make it clear that clinicians should encourage women 35 years or older to avoid rapid repeat pregnancy. The situation is complicated, however, by the decline in fertility that begins in the mid 30s and accelerates rapidly through the 40s.” They added, “Older women need to weigh the risks to their own health and their infants’ health against the risks of not achieving the number of children they want.”2