Short interpregnancy interval (IPI) is associated with preterm delivery in singleton live births from a national cohort undergoing assisted reproductive technology (ART)

Abstract

Short interpregnancy interval (IPI) has been associated with poor maternal and neonatal outcomes in the naturally conceiving population. As a result, a stated objective of Healthy People 2020 is to reduce by 10% pregnancies occurring within 18 months of delivery while the World Health Organization recommends an IPI of 24 months. Patients with a prior live birth from assisted reproductive technology (ART) may want to initiate treatment sooner given a history of infertility, particularly in the setting of advanced maternal age. However, no data exist on IPI and pregnancy outcomes in patients undergoing ART. We evaluated the strength and direction of associations between short IPI and adverse pregnancy outcomes in the population undergoing ART in a national dataset. Retrospective analysis of the Society for Assisted Reproductive Technology Clinic Outcome Reporting System (SARTCORS) cohort. Patients from SARTCORS with a history of live birth from ART who returned for a subsequent fresh in vitro fertilization (IVF) cycle from 2004-2013 were included. IPI was defined as interval from live birth to IVF cycle start. Singleton gestational age at delivery and birth weight were stratified by 6-month IPI intervals and compared by ANCOVA with adjustment for age and oocyte source. Logistic regression models of preterm delivery (<37 weeks) and low birth weight (<2500 grams) on IPI were fit with adjustment for age and oocyte source. Predicted probabilities for each dichotomous outcome were generated from the logistic model. Of 51,997 fresh IVF cycles following an index live birth, 17,536 resulted in a repeat live birth with 12,551 singleton live births. Forty percent of singleton live births occurred after an IPI of <18 months. Compared to a reference IPI of 18 to <24 months, the adjusted odds ratio for singleton preterm delivery was 1.73 [95%CI 1.19,2.51] for IPI <6 months, 1.57 [1.30,1.89] for IPI 6 to <12 months, 1.12 [0.95,1.33] for IPI 12 to <18 months, and 1.07 [0.92,1.26] for >24 months. IPI less than 12 months was associated with a higher predicted incidence of preterm delivery and low birth weight.Tabled 1Interpregnancy Interval (IPI), singletons<6 months n=2436 to <12 months n=1,63412 to <18 months n=3,12218 to <24 months n=2,749≥24 months n=4,803p-valueaPreterm delivery % (est) ±SEM15.9±2.4%bcd14.6±0.9%ecd10.9±0.6%9.8±0.6%10.5±0.4%<0.001Birth weight <2,500 grams % (est) ±SEM10.1±1.9%ecf8.7±0.7%ecd5.5±0.4%5.6±0.4%6.4±0.4%<0.001apredicted probabilities derived from logistic regression with adjustment for age and oocyte sourcebp=0.02 compared with 12 to <18 monthscp<0.01 compared with 18 to <24 monthsdp<0.01 compared with ≥24 monthsep<0.01 compared with 12 to <18 monthsfp=0.03 compared with ≥24 months Open table in a new tab apredicted probabilities derived from logistic regression with adjustment for age and oocyte source bp=0.02 compared with 12 to <18 months cp<0.01 compared with 18 to <24 months dp<0.01 compared with ≥24 months ep<0.01 compared with 12 to <18 months fp=0.03 compared with ≥24 months 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 in singleton live births from ART. The data support delaying the start of IVF treatment 12 months from live birth, but do not suggest a benefit from a longer interval as has been recommended for naturally conceiving couples.