Are live birth rates higher in women with greater endometrial thickness undergoing fresh embryo transfer?

This study investigated if there is a link between endometrial thickness (EMT) and live birth rate (LBR) in women undergoing in vitro fertilization (IVF) with fresh embryo transfer (FET). 

They found that thicker EMT is associated with higher LBR in these women. 

Infertility is an increasing problem worldwide. Assisted reproduction (AR) is used to treat couples with infertility. Fertility naturally declines in women over time. The number and quality of oocytes (eggs) declines. Endometrial receptivity (ER) also reduces with age. The endometrium is the lining of the womb. ER is important for embryos to implant and develop. ER is measured by endometrial thickness (EMT). EMT is usually measured before embryo transfer (ET).

A thin EMT usually suggests that there will be negative fertility outcomes. A thin EMT is anything less than 6 mm. Normal thickness is 7 mm or more. A thick EMT is more than 13 or 14 mm. Thin EMT is linked to poorer fertility outcomes. However, it is unclear if thicker EMT is associated with better birth rates during AR. 

This study included 2343 women undergoing 5133 IVF cycles with fresh ET. EMT was measured before fresh ET. The authors analyzed fertility outcomes including live birth rate (LBR). LBR was compared across 5 EMT groups. Group 1 had an EMT of 6 mm or less. Group 2 had 7-9 mm. Group 3 had 10-12 mm. Group 4 had 13-15 mm and group 5 had 16 mm or more. 

The lowest LBR (11.22%) was in women with EMT 6 mm or less. The highest LBR was in women with EMT 16 mm or more (34.21%). LBRs were increasingly higher with increasing EMT. Group 2 had a LBR of 17.98%, compared to 23.44% in group 3 and 25.62% in group 4. Younger women had higher LBRs. There was no link between EMT and pregnancy loss in each age group. 

The authors concluded that higher EMT is associated with higher LBR in women undergoing IVF with fresh ET.

This was a retrospective study, meaning it looked back at medical records data. Some data may not have been available. ET happened with fresh embryos on day 3. The effect of EMT on fertility outcomes could be different with other AR protocols. More studies are needed.