Serum progesterone day-of-transfer test falls short in frozen embryo transfers

Researchers at Sun Yat-Sen University found that a single serum progesterone measurement on embryo transfer day did not reliably predict success in frozen–thawed embryo transfer cycles using intramuscular progesterone. Embryo stage and quality were more important signals, suggesting fertility clinics should look beyond one hormone reading when guiding treatment.

Why it matters: - A day-of-transfer progesterone test is appealing because it is simple and could guide hormone dose adjustments in IVF. - This study suggests that one serum progesterone reading alone is not enough to predict frozen–thawed embryo transfer outcomes. - The finding could affect how fertility clinics monitor patients and decide whether to change progesterone support.

What happened: - Researchers from The First Affiliated Hospital of Sun Yat-Sen University in Guangzhou studied whether serum progesterone on embryo transfer day predicted pregnancy success in frozen–thawed embryo transfer cycles. - The team focused on single euploid blastocyst transfers in hormone replacement therapy cycles supported by intramuscular progesterone. - The findings were published in BJOG: An International Journal of Obstetrics & Gynaecology on April 15, 2025, and were available online on December 17, 2024.

The details: - The study was a retrospective analysis of clinical data from patients undergoing hormone replacement therapy-frozen embryo transfer. - Researchers compared live birth rate, clinical pregnancy rate and early pregnancy loss across three serum progesterone categories measured on the day of embryo transfer. - The overall live birth rate was about 55%. - Serum progesterone levels were similar in patients who had a live birth and those who did not. - Patients with both relatively lower and relatively higher progesterone levels on transfer day still achieved successful pregnancies. - Blastocyst developmental stage mattered more than the hormone reading, with day 5 embryos linked to better outcomes than day 6 embryos. - Overall embryo quality was also more strongly associated with live birth rate than serum progesterone on transfer day. - The original paper was titled “Serum Progesterone Level on the Day of Embryo Transfer Is Not a Reliable Predictor for Frozen–Thawed Embryo Transfer Outcomes With Euploid Blastocyst Transfer: A Retrospective Cohort Study.” - The paper’s DOI is 10.1111/1471-0528.18045.

Between the lines: - Previous research on progesterone thresholds has been inconsistent, in part because many studies did not fully account for embryo-related factors and often examined vaginal progesterone rather than intramuscular dosing. - The Sun Yat-Sen University team says that single serum progesterone measurements do not capture the full biology of implantation. - The results point to a broader view of IVF success that includes embryo competence, not just hormone levels. - This is analysis from a single retrospective cohort, so the findings are useful but not definitive.

What's next: - The researchers say randomized controlled trials are needed to test whether measuring progesterone and adjusting the dose improves outcomes. - Future fertility protocols may rely more on embryo stage and quality alongside hormonal support. - Better understanding of implantation biology could help refine treatment strategies for IVF patients.

The bottom line: - In frozen embryo transfer cycles using intramuscular progesterone, one serum progesterone check on transfer day does not appear to be a reliable stand-alone predictor of success.