‘A very unique observation’: Study links endometriosis to slightly higher birth-defect risk

A pregnant woman stands for a portrait in Dallas, Thursday, May 18, 2023. THE CANADIAN PRESS/AP, LM Otero

A new study shows that mothers with endometriosis face a slightly higher risk of giving birth to babies with birth defects.

The population-based study, published Monday by the Canadian Medical Association Journal (CMAJ), analyzed data of more than 1.4 million births in Ontario between April 7, 2006, and March 31, 2021.

Among those, 33,619 babies were born to people who had endometriosis, and of that amount, 2,120 babies had a congenital anomaly, representing a 6.3 per cent rate.

For babies born to people without endometriosis, 77,094 had a congenital anomaly, representing a 5.4 per cent rate. The increased risk observed in mothers with endometriosis is small, according to Dr. Olga Bougie, who developed the database used in the study. She is a gynecologic surgeon specializing in advanced endometriosis and other complex benign gynecologic conditions at Mount Sinai Hospital, and head of research in endometriosis and pelvic pain at Sinai Health.

But the findings are important, she says, because this is the first Canadian study to examine the health of babies born to mothers with endometriosis.

“Endometriosis really used to be a condition of ‘bad periods,’ but it has such a bigger impact across the lifespan of these patients,” she told CTVNews.ca in an interview. “Although many do experience pain, there’s implications beyond that.”

‘Very unique observation’

The study found that endometriosis — a gynecological condition in which tissue similar to that which lines the uterus and sheds each month during a menstrual cycle grows abnormally elsewhere in the body — was associated with an increased risk of cardiovascular, gastrointestinal, genital and musculoskeletal birth defects, including neoplasms and tumours.

Particularly, they saw a slightly increased risk for conditions like cleft palate, hypospadias and pulmonary artery stenosis.

In addition to severe cramps and chronic pelvic pain, endometriosis can also cause heavy bleeding and impact several organ systems in the body.

Prior research has also shown that people with endometriosis can experience infertility and have a higher risk of complications during pregnancy, Bougie says.

“And now we’re seeing that even beyond that, there may be a risk to the infants born to parents with endometriosis,” Bougie said. She is an associate professor of obstetrics and gynecology at the University of Toronto.

“This is a very unique observation, and it certainly warrants further investigation on whether people that have a pregnancy who have endometriosis need better imaging to screen for potential anomalies or better counseling.”

Bougie says fertility treatments can increase the risk of having a baby with a birth defect, and women with endometriosis may experience infertility and use such treatments. But she says the findings in this study showed that the increased risk was only partially due to fertility treatments, and that endometriosis itself is a contributing factor.

“There is an impact of endometriosis on the birth defects, but what we don’t know right now is how that is caused,” she said. “Is it the treatments for endometriosis? Is it something about the condition? We know that endometriosis causes a lot of inflammation in the body; is that the reason for these anomalies? (...) this warrants further exploration.”

More funding for research needed

Endometriosis impacts roughly one million people in Canada, making it one of the most prevalent gynecological conditions.

It is one of many areas of women’s health care that has been chronically underfunded.

• READ MORE: Researchers use AI to speed up endometriosis diagnoses in Canada

“Some studies suggest up to 15 per cent of individuals with a uterus have endometriosis,” Bougie said. “The funding that endometriosis receives is really not congruent with that number.”

Bill S-243 was introduced by the federal government in December 2025 to establish a national framework for women’s health. It aims to remedy historical inequities in health research and health care in Canada.

Bougie says more research on the multifaceted impacts of endometriosis is needed.

“A lot of the research and treatments are very focused on the pain,” she said. “We don’t have a more holistic look at the impact of endometriosis across their lives.”

“When people come in with fertility, our goal is to get them pregnant. We don’t have as much research and counseling about the impact of endometriosis on the pregnancy or the children born to these parents.”