O-207 Comparison of the pregnancy outcomes of transferring frozen embryos versus fresh embryos among advanced maternal age women: a nationwide analysis of 232,942 cycles
Authors: Wang Z , Liu C , Kong N , Yan G , Sun H 
Published: July 2024

Abstract

Study question
Are there differences in pregnancy outcomes when comparing frozen embryo transfer versus fresh embryo transfer among aged women?

Summary answer
Frozen embryo transfer yields lower live birth rate for women aged 35-39, but higher rate for women ≥40 compared to fresh embryo transfer.

What is known already
Advanced maternal age was defined as over 35 years old, while recent literature lifted the threshold to 40. An increasing number of women are postponing childbirth, but reproductive issues become more common after the age of 35, with a significant decline in fertility, particularly after 40, even with IVF. Advanced age affects pregnancy rates, prompting some clinicians to prefer fresh embryo transfer to achieve pregnancy quickly. However, it may be less effective with potential negative effects of ovarian stimulation on endometrial receptivity. Frozen embryo transfer is seen as a better strategy, but data specific to advanced maternal age is lacking.

Study design, size, duration
This cohort study analyzed the Human Fertilization and Embryology Authority anonymized data from 2011 to 2018 in the United Kingdom. This comprised of a total of 232,942 cycles with advanced maternal age, in which 65,066 patients undergoing frozen embryo transfer cycles, and 167,876 patients undergoing fresh embryo transfer cycles.

Participants/materials, setting, methods
Data on women with advanced maternal age undergoing IVF/ICSI cycles were analyzed to compare live birth rate and miscarriage rate. The cycles with patients’ age &lt;35, donor oocyte / embryo, PGT, or without embryo to transfer were excluded. Log-binominal regression analysis was performed adjusting for patient age, cause of infertility, number of embryos transferred, year of treatment, and IVF or ICSI cycle.

Main results and the role of chance
We analyzed data from 232,942 cycles with patients age ≥35, and found that FET cycles exhibited a higher live birth rate than that of fresh embryo transfer cycles (25.5% vs. 24.9%, RR, 1.03; 95% CI, 1.01–1.123). Miscarriage rate (4.6% vs. 3.3%, RR, 1.41; 95% CI, 1.35–1.48) was also different. However, the adjusted RR (aRR) of live birth rate was 0.91; 95% CI, 0.88–0.93, after adjusting for potential confounders. For those patients aged 35-39, live birth rate (28.4% vs. 29.7%, aRR, 0.86; 95% CI, 0.83–0.88) following FET cycles was lower than that of fresh embryo transfer cycles. While FET cycles showed a higher rate of miscarriage (4.6% vs. 3.2%, aRR, 1.83; 95% CI, 1.70–1.98). When patients age≥40, FET cycles showed a higher rate of live birth (18.2% vs. 14.0%, aRR, 1.24; 95% CI, 1.16–1.32) and miscarriage rate (4.7% vs. 3.4%, aRR, 1.72; 95% CI, 1.52–1.94). Besides the live birth rate was sharply decreased than patients aged 35-39 both in FET and fresh embryo transfer cycles.

Limitations, reasons for caution
The conclusion of the present study might be limited by the anonymous nature of the dataset. Further randomized trials may be required to provide direct evidence for the best embryo transfer strategy for the advanced age women.

Wider implications of the findings
The study shows that FET exhibited a higher live birth rate in women aged ≥ 40, but lower for those aged 35-39 than fresh embryo transfer. Additionally, FET demonstrated a higher miscarriage rate. Therefore, it is necessary to tailor the embryo transfer strategy for advanced maternal age women.

Trial registration number
not applicable