The United States has the highest maternal mortality rate in the developed world. Strokes account for about 7.5 percent of pregnancy-related deaths.

At the same time, use of assisted reproductive technology has risen dramatically over the past 10 years. About 2 percent of births in the United States involve infertility treatment of some kind, according to the paper.

In the new study, researchers defined these measures to include intrauterine insemination, assisted reproductive technology, use of a surrogate and fertility preservation procedures.

While infertility treatments are generally safe, some studies have linked them to increased risks during pregnancy, including higher rates of pre-eclampsia — a potentially deadly complication involving extremely high blood pressure — as well as placental abnormalities and preterm birth.

Previous studies of stroke after infertility treatments have yielded mixed results. The new study, published in JAMA Network, is believed to be the largest to examine the risk of hospitalization for stroke among these women.

It analyzed the health outcomes of 31 million patients who had a hospital delivery in 28 states between 2010 and 2018, including 287,813 who had undergone infertility treatments.

The risk of a hemorrhagic stroke — bleeding in the brain — was twice as high among women who had undergone fertility treatment, compared to those who did not, the study found.

The odds of an ischemic stroke, which occurs when the blood supply to the brain is interrupted, was 55 percent greater, compared with women who conceived naturally.

These results are not the final word on the subject, however.

Just a few weeks ago, the journal JAMA Cardiology published a study that examined long-term health outcomes among women in four Scandinavian countries who had received infertility treatments, and found no evidence of an increased risk for cardiovascular disease.

That study was much smaller, however, including only 2.4 million women.

The new research did not include data about important risk factors for stroke, such as smoking, body mass index and hypertension. The scientists took steps to account for the missing data and still found a heightened risk, said the paper’s senior author, Cande V. Ananth, chief of epidemiology and biostatistics at the Robert Wood Johnson Medical School in New Jersey.

In an interview, Dr. Ananth outlined three possible explanations for a link between stroke and infertility treatment.

“We know that women who receive infertility treatment have certain vascular complications, typically an increased risk of pre-eclampsia and placental abruption,” he said.

Second, infertility treatments can bring physiological changes, he said. Patients often receive large amounts of estrogen, for example, which can lead to increased blood clotting, a strong risk factor for stroke, he said.

Third, he added, “is that people who receive the treatment receive it for a reason. Perhaps there are different biological characteristics” among women seeking treatment, he said.

Still, stroke remains very infrequent among women after childbirth, whether they received treatments or not, Dr. Ananth said. “Patients should be aware of the impending risks and counseled appropriately,” he said.

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