Women undergoing in vitro fertilization (IVF) may have one less concern, a new study suggests.
Research published in Human Reproduction indicates that a thin endometrial lining—the inner uterine layer that supports a fertilized embryo—does not necessarily reduce the likelihood of a successful IVF pregnancy.
For years, fertility specialists believed that a thin endometrium could hinder embryo implantation. However, the study shows that many women with thin linings can still achieve live births.
“In the overall population, many patients may have a thin lining, which should not decrease their success rates,” said senior researcher Dr. Emre Seli, professor of obstetrics, gynecology, and reproductive sciences at Yale School of Medicine in New Haven, Connecticut.
The study analyzed more than 30,000 IVF cycles between January 2017 and December 2022 at fertility clinics in the U.S., Spain, and the United Arab Emirates (UAE). Researchers defined a thin endometrium as less than 7 millimeters in thickness.
Findings revealed that only 3% of embryo transfers in the U.S. and 5% in Spain involved thin endometria, suggesting that some clinics may avoid IVF in these patients. In contrast, about 12% of transfers in the UAE involved thin linings, reflecting less concern about potential complications.
Among UAE clinics, thin endometria did not correlate with lower birth rates. In U.S. and Spanish clinics, women with linings under 7 millimeters had roughly 20% fewer live births—but researchers caution that this does not reflect the lining itself.
“In many cases, women with thin endometria receive medications to increase thickness. If the lining remains unresponsive, IVF cycles may be canceled,” Seli explained. “It’s likely not the thin lining itself causing reduced success, but an underlying factor that contributes both to persistent thinness and lower implantation rates.”
The study also found that women with linings under 5 millimeters still achieved successful pregnancies, highlighting that even very thin endometria can support embryo implantation.
“One can have a baby at 4, 5, 6 millimeters with just a slightly decreased success rate,” Seli said.
The research team is now developing a predictive calculator to help fertility specialists provide patients with more personalized assessments of their IVF success chances.
YOU MAY ALSO LIKE
Scientists Capture First IVF Embryo Implantation in Real Time
Nepal Government Sets Uniform Guidelines for IVF and Fertility Services
Study Uncovers How Fat Cells May Fuel Aggressive Breast Cancer
