While only a small association, experts are warning it is significant and requires further investigation.
Babies born to women with endometriosis had a 16% higher relative risk of congenital anomalies, a large Canadian population-based observational study has found.
Among infants with congenital anomalies, 6.3% had a parent diagnosed with endometriosis, compared with 5.4% among those without anomalies (RR 1.16).
The study used data of more than 1.4 million births in Ontario between 2006 and 2021, showing the most common defects associated with endometriosis were cleft palate (RR 1.52) hypospadias (RR 1.47) and pulmonary artery stenosis (RR 1.41).
Those with endometriosis were more likely to have conceived with IVF than those without (10.6% vs 1.5%), but researchers said the association between endometriosis and birth defects were independent of this.
Around 11% of the increased relative risk was explained by IVF or ICSI, and other fertility-related factors such as subfertility, ovulation induction and intrauterine insemination also didn’t appear to mediate the relationship between endometriosis and congenital anomalies.
The researchers also adjusted for factors associated with increased risk of congenital abnormalities, including age, diabetes, high blood pressure, smoking status, alcohol and substance use, obesity and income.
The highlighted that although the relative risk increase was modest and should be investigated further, the absolute risk remained low.
“That is an impressive study size and should be taken seriously,” Dr Tal Jacobson, consultant gynaecologist at Eve Health and Mater Hospital Brisbane and clinical senior lecturer at the University of Queensland, told media.
“The authors suggest that the reasons [for the association] may be to do with increased inflammation in endometriosis patients affecting embryological pathways.”
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He highlighted some limitations to the research, including the low prevalence of women with endometriosis in the study, which accounted for 2.3% (33,619) of mothers, despite an expected prevalence of around one in 10.
“The diagnosis of endometriosis was based on hospital procedure codes; the outcomes regarding congenital anomalies used hospital databases. These are prone to error and bias,” he said.
Dr Kelsi Dodds, a National Endometriosis Clinical and Scientific Trials (NECST) Postdoctoral Fellow at Adelaide University, also highlighted this issue, telling media that endometriosis was notoriously underdiagnosed.
“It is plausible that many women with ‘no endometriosis’ had undiagnosed endometriosis,” Dr Dodds said.
“If the true incidence of endometriosis was known, it is possible that the purportedly increased risk may disappear.”
Dr Jacobsom agreed.
“I would conclude from this study that there is a possible small increased risk of congenital abnormality if you have endometriosis,” said Dr Jacobson.
“This result should not deter anyone with endometriosis from having a baby, but it should inspire more research into this association to try and determine the cause and develop potential interventions.”
“These findings are not a cause for alarm, rather a call to action,” said Dr Dodds.
“Efforts to diagnose endometriosis earlier could mitigate disease progression and thus possibly reduce the potential increased burden of congenital abnormalities.”
