Endometrial Thickness of 9.4 mm on Day 4 of Cycle for Donor Embryo Transfer
An endometrial thickness of 9.4 mm on day 4 of the menstrual cycle is adequate for proceeding with donor embryo transfer, and you should transfer only a single embryo regardless of this measurement, the mild adenomyosis, or the small ovarian cyst. 1
Mandatory Single Embryo Transfer for Donor Embryos
The European Society of Human Reproduction and Embryology (ESHRE) mandates elective single embryo transfer (eSET) for all donated embryo transfers, with no exceptions based on endometrial thickness, mild adenomyosis, or presence of small ovarian cysts. 1
This is a strong recommendation that applies regardless of endometrial characteristics, patient age, number of previous unsuccessful treatments, duration of infertility, or ovarian response. 1
ESHRE guidelines explicitly state that endometrial characteristics should not determine whether to perform single versus double embryo transfer in frozen embryo transfer cycles, prioritizing avoidance of multiple pregnancy risks. 1
Endometrial Thickness Assessment
The 9.4 mm endometrial thickness on day 4 is well above the threshold associated with successful implantation. 2, 3
Research demonstrates that endometrial thickness >9 mm is associated with significantly higher embryo implantation rates (24.4% vs 14.3%), clinical pregnancy rates (48.6% vs 16.0%), and ongoing pregnancy rates (42.2% vs 11.7%) compared to thickness <9 mm. 2
A large retrospective study of 1,294 IVF cycles showed clinical pregnancy rates increased from 53% with endometrium <9 mm to 77% with endometrium ≥16 mm, with live-birth rates reaching a plateau at 11 mm thickness. 3, 4
However, the independent contribution of endometrial thickness to live birth is actually quite small - multivariate analysis shows that a 2 mm increase in endometrial thickness results in only approximately 1.6% increase in live birth rate when controlling for other factors. 5
Clinical Implications for This Case
The presence of mild adenomyosis does not change the recommendation for single embryo transfer and should not be considered a reason to transfer multiple embryos. 1
The 11 mm ovarian cyst is classified as O-RADS 2 (almost certainly benign, <1% risk of malignancy) if it is a simple or classic benign lesion less than 10 cm, and does not contraindicate embryo transfer. 6
Focus on preventing multiple pregnancy complications, which would be particularly problematic in a uterus with adenomyosis. 1
Counseling Points
Counsel the patient that eSET is the standard of care for donor embryo transfers to minimize maternal and neonatal complications. 1
The multiple pregnancy rate is 30-fold higher with double embryo transfer compared to repeated single embryo transfer (OR 30.54,95% CI 7.46-124.95). 1
Cumulative live birth rates with repeated single embryo transfer are equivalent to double embryo transfer while avoiding twin risks including pre-eclampsia, gestational diabetes, emergency cesarean section, and preterm labor. 1