Interpregnancy interval and singleton pregnancy outcomes after frozen embryo transfer.

OBJECTIVE

To describe the relationship between interpregnancy interval (IPI) and perinatal outcomes in singleton live births after frozen embryo transfer (FET).

DESIGN

Retrospective analysis of the Society for Assisted Reproductive Technology Clinical Outcome Reporting System cohort including patients with a history of live birth from ART who returned for an FET cycle between 2004 and 2013.

SETTING

Not applicable.

PATIENT(S): A total of 19,270 singleton live births from FET subsequent to a live birth.

INTERVENTION(S): None.

MAIN OUTCOME MEASURE(S): Odds for preterm delivery (<37, <34, <28 weeks) and low birth weight (<2,500, <1,500 g) adjusted for age, body mass index, and history of prior preterm delivery.

RESULT(S): Of 74,456 autologous FET cycles following an index live birth, 24,091 resulted in a repeat live birth, with 19,270 singleton live births. An IPI of <12 months occurred in 19% of cycles. Adjusted odds (aORs) for preterm delivery at <37 weeks were significantly increased for an IPI of <6 months (aOR 2.05, 95% confidence interval [CI] 1.48-2.84), 6 to <12 months (aOR 1.26, 95% CI 1.06-1.49), and 18 to <24 months (aOR 1.23, 95% CI 1.06-1.43) when compared with the reference interval of 12 to <18 months. Additionally, an IPI of <6 months was associated with increased odds for low birth weight (aOR 3.06, 95% CI 2.07-4.52) and very low birth weight (aOR 5.65, 95% CI 2.96-10.84) compared with an IPI of 12 to <18 months.

CONCLUSION(S): In this nationally representative population, an interval from delivery to start of an FET cycle of <12 months is associated with increased odds for preterm delivery among singleton live births. Consistent with data for patients undergoing fresh IVF, the data support delaying FET 12 months from a live birth.