Shorter, longer interpregnancy intervals tied to spontaneous abortion risk

Key takeaways:

• Interpregnancy intervals shorter than 18 months were tied to higher risk for spontaneous abortion.
• Interpregnancy intervals of 36 to 59 or at least 60 months were tied to higher spontaneous abortion risk.

After a healthy live birth, interpregnancy intervals shorter than 18 months or 36 months or longer were associated with an increased risk for subsequent spontaneous abortion, according to cohort study results published in JAMA Network Open.

“Some scholars have proposed that the interpregnancy interval is a potential modifiable risk factor for adverse pregnancy outcomes, and previous evidence has shown that a short interpregnancy interval after an abortion may reduce the risk of a subsequent spontaneous abortion,” Xuan Hu, BA, from the National Research Institute for Family Planning, the department of epidemiology and health statistics at the School of Public Health at the Medical College of Soochow University and the National Human Genetic Resources Center, Beijing, and colleagues wrote. “Nevertheless, the association between interpregnancy interval after live birth and subsequent spontaneous abortion is less studied and remains unclear, particularly among parous women with healthy live births.”

Hu and colleagues conducted a prospective cohort study using data from the Chinese National Free Prepregnancy Checkups Project from 2010 to 2020 from 180,921 multiparous women (mean age, 26.3 years) aged 20 to 49 years with a single healthy live birth who were planning for another pregnancy. Researchers investigated the association between interpregnancy intervals shorter than 18 months, 18 to 23 months, 24 to 35 months, 36 to 59 months or 60 months or longer after a healthy pregnancy and subsequent spontaneous abortion.

Interpregnancy intervals were shorter than 18 months for 37.4% of women, 18 to 23 months for 16.2%, 24 to 35 months for 25.2%, 36 to 59 months for 19.1% and 60 months or longer for 2.1%.

Overall, 2.4% of women experienced a subsequent spontaneous abortion. Of spontaneous abortions, 2.3% occurred among women with interpregnancy intervals shorter than 18 months, 2.1% among women with intervals of 18 to 23 months, 2.3% among women with intervals of 24 to 35 months, 2.8% among women with intervals of 36 to 59 months and 4.9% among women with intervals of 60 months or longer.

Researchers observed a nonlinear association between interpregnancy intervals and spontaneous abortion.

In adjusted models, women with interpregnancy intervals shorter than 18 months had a 15% higher risk for spontaneous abortion compared with intervals of 18 to 23 months (OR = 1.15; 95% CI, 1.04-1.27). Compared with interpregnancy intervals of 18 to 23 months, women with intervals of 36 to 59 months (OR = 1.28; 95% CI, 1.15-1.43) and 60 months or longer (OR = 2.13; 95% CI, 1.78-2.56) had a 28% and 113% higher risk for spontaneous abortion, respectively.

“These findings are potentially valuable to clinicians when providing fertility counseling and to families when making a rational birth plan; these results may also facilitate the prevention of spontaneous abortion and improvement in neonatal outcomes,” the researchers wrote.