Factors associated with large-for-gestational-age infants born after frozen embryo transfer cycles

OBJECTIVE: To examine trends of frozen embryo transfer (FET) proportions and large-for-gestational-age (LGA) incidence and determine risk factors for LGA infants after FET. DESIGN: Retrospective cohort study. SETTING: Not applicable. PATIENT(S): Frozen embryo transfer cycles. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Singleton LGA infant. RESULT(S): The percentage of FETs increased from 20%–74% of transfers, whereas the rate of LGA among FET singleton births decreased from 18%–12% during 2004–2018. In a subanalysis of 127,525 FET-associated singleton live births during 2016–2018, patient factors associated with LGA were higher-than-normal maternal body mass index (body mass index [BMI], 25.0–29.9 kg/m(2); adjusted relative risk [aRR], 1.31; 95% confidence interval [CI], 1.26–1.36; BMI, 30.0–34.9 kg/m(2); aRR, 1.48; 95% CI, 1.41–1.55; and BMI, >35 Kg/m(2); aRR, 1.68; 95% CI, 1.59–1.77) and ≥1 prior birth vs. none. Low maternal BMI (<18.5 vs. 18.5–24.9 kg/m(2)) and cycles involving patients who were non-Hispanic (NH) Asian/Native Hawaiian/Pacific Islander, NH Black, or Hispanic (compared with NH White) were at lower risk of LGA infants. Cycle factors associated with LGA included gestational carrier use (aRR, 1.25; 95% CI, 1.16–1.34) and donor sperm (aRR, 1.17; 95% CI, 1.10–1.25). CONCLUSION(S): Although the number and proportion of FET cycles increased from 2004–2018, the rate of LGA after FET decreased. Maternal BMI, parity, and race/ethnicity were the strongest risk factors for LGA infants after FET.