The impact of fresh versus frozen-thawed embryos on maternal serum analyte levels in IVF singleton and twin pregnancies.

PURPOSE: To determine whether embryo cryopreservation is associated with a difference in maternal serum analyte levels in singleton and twin pregnancies conceived via in vitro fertilization (IVF).

METHODS: This was a retrospective cohort study of singleton and twin pregnancies conceived via IVF from a university health system from 01/2014 to 09/2019. Patients with available first and second trimester serum analyte data were included and analyzed separately. Multiple of the median (MoM) values for free β-human chorionic gonadotropin (β-hCG), pregnancy-associated plasma protein A, alpha-fetoprotein (AFP), Inhibin A, and unconjugated estriol (uE3) were compared between two groups: pregnancies conceived after the transfer of fresh embryos versus pregnancies conceived after the transfer of frozen-thawed embryos. Multiple linear regression of log MoM values with F test was performed to adjust for potential confounders.

RESULTS: For singletons, fresh embryos were associated with a lower median first trimester free β-hCG (1.00 MoM vs. 1.14 MoM; parameter estimate [PE] 0.90, 95% CI 0.82-0.99, p = .03) compared to frozen-thawed embryos. Fresh embryos were also associated with a lower median second trimester uE3 (0.93 MoM vs. 1.05 MoM; PE 0.88, CI 0.83-0.95, p = .0004) and AFP (1.02 MoM vs. 1.19 MoM; PE 0.91, CI 0.84-0.99, p = .02) compared to frozen-thawed embryos in singletons. There were no significant differences between median first and second trimester serum analytes in twin pregnancies compared between the two groups.

CONCLUSION: Singleton pregnancies derived from fresh embryos had lower first (free β-hCG) and second (uE3 and AFP) trimester analytes compared to frozen-thawed embryos. Twin pregnancies demonstrated no difference between the groups.