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

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.

Retrospective cohort study.

Not applicable.

Frozen embryo transfer cycles.

None.

Singleton LGA infant.

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/m²; adjusted relative risk [aRR], 1.31; 95% confidence interval [CI], 1.26-1.36; BMI, 30.0-34.9 kg/m²; aRR, 1.48; 95% CI, 1.41-1.55; and BMI, >35 Kg/m²; 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/m²) 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).

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.