Is there an optimal endometrial thickness to maintain pregnancy after embryo transfer?

This study investigated if there is a link between endometrial thickness (EMT) and live birth rate (LBR) after embryo transfer (ET). They found that EMT equal to or greater than 10 mm was linked to a higher LBR.

Assisted reproductive technologies (ART) are used to treat infertility. In vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) are methods used to fertilize an egg in a lab. The fertilized egg or embryo is later transferred to the uterus (womb). Embryo transfer (ET) is performed when the embryo is mature. Before ET, the uterus lining (endometrium, EM) must be formed. Endometrial thickness (EMT) is an important factor for ART success. The EM supplies growth factors and hormones that support the developing embryo. 

Although EMT is considered to be an important factor, there is no ‘ideal’ EMT. Guidelines suggest performing ET with an EMT of 5 mm thickness or greater. It is unclear of EMT thickness has an impact on the pregnancy (PR) or live birth rate (LBR).

This study included 25,767 IVF/ICSI cycles. These were performed in 21,752 women. The authors analyzed patient records. EMT was measured using a transvaginal ultrasound. The main outcomes of interest were PR, pregnancy loss rate (PLR) and LBR. 

The average EMT was 11.3mm. LBR was significantly greater in cycles with EMT of 10 mm or greater compared to 5 mm or less (33.1% vs. 15.6%). PRs were also higher with an EMT of 10 mm or greater. PLR was 41.7% in cycles with EMT of 5 mm or less. This compares to a PLR of 26.5% in cycles with EMT of 10 mm or greater. Implantation rates also increased with increasing EMT.

The authors concluded that EMT equal to or greater than 10 mm was linked to a higher LBR.

This study analyzed cycles with fresh ET. Frozen ET is also frequently used. The optimal EMT in frozen ET may be different. 

If you have any concerns regarding fertility treatment, please consult with your doctor.