Interpregnancy Interval and Singleton Live Birth Outcomes From In Vitro Fertilization.

OBJECTIVE

To describe the relationship between a short interpregnancy interval and adverse pregnancy outcomes in the population undergoing assisted reproductive technology.

METHODS

This is a retrospective analysis using data from the Society for Assisted Reproductive Technology Clinic Outcome Reporting System. The cohort includes patients with a history of live birth from assisted reproductive technology who returned for a fresh, autologous in vitro fertilization (IVF) cycle from 2004 to 2013. Interpregnancy interval was defined as the interval from live birth to cycle start. Logistic regression models of preterm delivery (less than 37 weeks of gestation) and low birth weight (less than 2,500 g) on interpregnancy interval were fit with adjustment for age, body mass index, and history of preterm delivery. Predicted probabilities were generated from the logistic model.

RESULTS

Of 51,997 fresh IVF cycles after an index live birth, 17,536 resulted in a repeat live birth with 11,271 singleton live births from autologous IVF. An interpregnancy interval of less than 18 months occurred in 40.9% of cycles. Compared with a reference interpregnancy interval of 12 to less than 18 months, the adjusted odds ratio for singleton preterm delivery was 1.66 (95% CI 1.05-2.65) for an interpregnancy interval less than 6 months and 1.34 (95% CI 1.06-1.69) for 6 to less than 12 months. An interpregnancy interval 6 to less than 12 months was associated with a 3.0% increase in preterm delivery (13.6±1.1% vs 10.6±0.7%, P=.030) and a 2.7% increase in low birth weight (8.0±0.9% vs 5.3±0.5%, P=.025) compared with an interpregnancy interval of 12 to less than 18 months.

CONCLUSION

In this nationally representative population, an interval from delivery to treatment start of less than 12 months is associated with increased rates of preterm delivery and low birth weight in singleton live births from assisted reproductive technology. The data support delaying the start of IVF treatment 12 months from a live birth, but do not suggest a benefit from a longer interval as has been recommended for naturally conceiving couples.