Short interpregnancy intervals carry an increased risk of adverse pregnancy outcomes for women of all ages and increased adverse fetal and infant outcome risks for women between 20 and 34 years old, according to research published in JAMA Internal Medicine.

“This finding may be reassuring particularly for older women who must weigh the competing risks of increasing maternal age with longer interpregnancy intervals (including infertility and chromosomal anomalies) against the risks of short interpregnancy intervals,” wrote Laura Schummers, SD, of the department of epidemiology at Harvard T. H. Chan School of Public Health, Boston, and her colleagues.

The researchers examined 148,544 pregnancies of women in British Columbia who were younger than 20 years old at the index (5%), 20-34 years at the index birth (83%), and 35 years or older (12%). The women had two or more consecutive singleton pregnancies that resulted in a live birth between 2004 and 2014 and were recorded in the British Columbia Perinatal Data Registry. There was a lower number of short interpregnancy intervals, defined as less than 6 months between the index and second pregnancy, among women in the 35-years-or-older group, compared with the 20- to 34-year-old group (4.4% vs. 5.5%); the 35-years-or-older group instead had a higher number of interpregnancy intervals between 6 and 11 months and between 12 and 17 months, compared with the 20- to 34-year-old group (17.7% vs. 16.6%, and 25.2% vs. 22.5%, respectively).

The risk for maternal mortality or severe morbidity was higher in women who were a minimum 35 years old with 6 months between pregnancies (0.62%), compared with women who had 18 months (0.26%) between pregnancies (adjusted relative risk [aRR], 2.39). There was no significant increase in those aged between 20 and 34 years at 6 months, compared with 18 months (0.23% vs. 0.25%; aRR, 0.92). However, the 20- to 34-year-old group did have an increased risk of fetal and infant adverse outcomes at 6 months, compared with 18 months (2.0% vs. 1.4%; aRR, 1.42) and compared with women in the 35-years-or-older group at 6 months and 18 months (2.1% vs. 1.8%; aRR, 1.15).

There was a 5.3% increased risk at 6 months and a 3.2% increased risk at 18 months of spontaneous preterm delivery in the 20- to 34-year-old group (aRR, 1.65), compared with a 5.0% risk at 6 months and 3.6% at 18 months in the 35-years-or-older group (aRR, 1.40). The researchers noted “modest increases” in newborns who were born small for their gestational age and indicated preterm delivery at short intervals that did not differ by age group.

The authors reported no conflicts of interest. Dr Schummers was supported a National Research Service Award from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and received a grant from the Canadian Institutes for Health Research and the Public Health Agency of Canada Family Planning Public Health Chair Seed Grant. Two of her coauthors were supported by various other awards.

SOURCE: Schummers L et al. JAMA Intern Med. 2018 Oct 29. doi: 10.1001/jamainternmed.2018.4696.