Is endometrial thickness associated with higher risk of small-for-gestational age infants?

This study investigated if endometrial thickness (EMT) is associated with neonatal outcomes after fresh embryo transfer (Fr-ET). They found that a low EMT was associated with the risk of small-for-gestational-age (SGA) infants.

Assisted reproduction (AR) is used to treat infertility. Procedures like in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are used in AR. After IVF/ICSI fertilized embryos can be transferred to the uterus. This is called a fresh embryo transfer (Fr-ET). Embryos can also be frozen and transferred at a later stage (Fz-ET). The benefit of Fz-ET is it allows transfer at the optimal stage. 

After transfer, the embryo attaches to the endometrium (EM). The EM is the lining of the uterus. Endometrial thickness (EMT) is important for a successful ET. Some studies suggest that Fz-ET has better outcomes for the infant (neonatal outcomes). This may be because Fz-ET can be performed when the EM is at its optimal thickness. This is not always possible with Fr-ET. It is unclear if there is an association between EMT and neonatal outcomes in infants born from Fr-ET.

This study included 3157 women that underwent IVF/ICSI and Fr-ET. Women were categorized according to EMT. The groups were EMT below 7.5 mm, 7.5- 12 mm and more than 12 mm. The main outcomes measured included small-for-gestational-age (SGA) infants and preterm delivery (PTD). 

The rate of SGA infants was higher (8.3%) in women with EMT less than 7.5 mm. The risk of SGA was 2.39 times higher in this group compared to EMT of 12 mm or more. There were no differences in the rates of PTD or cesarian section. Other outcomes such as gestational diabetes and placenta previa (pregnancy complications) were not affected by EMT.

The authors concluded that a low EMT was associated with the risk of SGA infants in women undergoing IFV/ICSI with Fr-ET.

This study was based on medical records. The type of infertility and hormone levels were significantly different between the EMT groups. These factors could also influence the risk of SGA. 

If you have any concerns regarding infertility please consult with your doctor.