Factors associated with short interpregnancy interval among women treated with in vitro fertilization.

PURPOSE: To evaluate factors associated with interpregnancy interval (IPI) among women treated with in vitro fertilization (IVF).

METHODS: Women with at least two cycles of IVF between 2004 and 2013 were identified from the SART CORS database and grouped by age at first cycle, infertility diagnosis, IVF treatment parameters, and cycle 1 outcome (singleton or multiple live birth or no live birth, length of gestation, and birthweight). The distributions of IPIs (in months, 0-5, 6-11, 12-17, 18-23, and ≥ 24) were compared across these factors. IPI was fit as a function of these factors by a general linear model, separately for singleton and multiple live births and no live births at cycle 1.

RESULTS: The study included 93,546 women with two consecutive IVF cycles where the first cycle resulted in a clinical intrauterine pregnancy or a live birth. Among women with a live birth in cycle 1, there was a general pattern of longer IPI for younger women compared to older women. Women with a multiple birth waited longer before initiating a second cycle than women with a singleton birth. For women with no live birth in the first cycle, nearly three fourths initiated cycle 2 within 6 months, regardless of their age. Short (0-5 months) IPI was associated with preterm delivery, older maternal age, and use of donor oocytes.

CONCLUSIONS: Age of the mother, outcome of the first pregnancy, and treatment factors affect the length of the interpregnancy interval. Because short IPI has been associated with poor outcomes, women who are at risk for short IPI should be counseled about these outcome risks.