Higher endometrial thickness prior frozen embryo transfer is associated with lower first-trimester placental growth...

To investigate the potential interaction between endometrial thickness before Frozen Embryo Transfer and Placental Growth Factor levels during the first trimester screening of pregnancy.

This single-centre retrospective observational study was conducted at the Reproductive Medicine Department of Dexeus University Hospital between January 2021 and June 2025. The analysis included singleton pregnancies resulting from both Artificial Cycle Frozen Embryo Transfer and Natural Cycle Frozen Embryo Transfer. All participants attended first-trimester pregnancy screening and delivered at Dexeus University Hospital in Barcelona, Spain.

Overall, 1,757 singleton pregnancies after Frozen Embryo Transfer were analysed, including 1,080 autologous and 677 heterologous cycles. Higher endometrial thickness (>12  mm) was associated with lower first-trimester Placental Growth Factor levels (24.9 ± 16.3 vs. 29.6 ± 16.3  pg/mL; p = 0.04), a finding that remained significant after Multiples of the Median adjustment (0.80 ± 0.29 vs. 0.90 ± 0.35; p = 0.013) and Log10 transformation (-0.12 ± 0.16 vs. - 0.08 ± 0.18; p = 0.029). Linear regression confirmed a negative correlation between endometrial thickness and log10 MoM Placental Growth Factor (β =  - 0.01; 95% CI - 0.01 to 0.00; p = 0.020). Obstetric and perinatal outcomes, including gestational age at delivery, birthweight, and the incidence of Hypertensive Disorders of Pregnancy, did not differ between groups.

Our findings suggest a negative association between endometrial thickness prior to frozen embryo transfer and first-trimester placental growth factor levels. Further studies are warranted to confirm these results and to better elucidate the mechanisms underlying the potential impact of endometrial thickness on early placental angiogenesis.