People who've had a miscarriage may have a higher risk of stroke, study suggests

• Infertility and pregnancy loss are linked to a slightly higher risk of stroke, a large study finds.
• The study looked at 620,000 women in 7 countries, finding recurrent losses raised stroke risk most.

Women who've experienced infertility, miscarriage, or stillbirth may be at a slightly increased risk of stroke, a study out Wednesday in the journal BMJ found.

The report, which analyzed data from eight studies across seven countries, suggests women who've suffered from infertility or pregnancy loss should be monitored and counseled on how to lower their risk of stroke, the authors say.

But an OB-GYN not involved with the study says the findings should be interpreted cautiously, as its design had significant limitations and the link discovered is relatively weak.

"It is important for women to understand that there are many different causes or pathways that can lead to infertility, recurrent pregnancy loss, and stillbirth," the doctor, Dr. Patrick Ramsey of UT Health San Antonio, told Insider. "Similarly, there are multiple pathways to increase a patient's risk for development of stroke."

Because the research couldn't parse those causes apart, "it is nearly impossible to apply the knowledge from this study to a given patient," he added.

The study found women who'd experienced multiple stillbirths were at highest risk of fatal strokes

Women are more likely to have a stroke, and to die from one, than men. In fact, it's the No. 3 cause of death in women, according to the American Heart Association. And while certain factors like high blood pressure and diabetes raise the risk, they don't fully explain why women are more susceptible.

Past research on adverse pregnancy outcomes and stroke have been inconclusive, so the authors of the current study wanted to dig deeper.

To conduct the analysis, they looked at a database tracking reproductive health and chronic disease in women from Australia, China, Japan, Netherlands, Sweden, UK, and the US. In all, around 620,000 women in their 30s to 70s were included.

Using questionnaires and hospital records, the researchers found women with history of infertility were at a 14% higher risk of non-fatal stroke than women without infertility. Those who'd had a miscarriage had a 11% higher risk than those who hadn't experienced miscarriage, and those who'd suffered a stillbirth had an over 30% higher risk than those without a stillbirth history.

The more miscarriages, the higher the risk, the study found. And when it came to fatal strokes, women who'd had multiple stillbirths were most at risk.

Still, of the data available, just 2.8% of participants suffered a non-fatal stroke and 0.7% experienced a deadly one.

Other medical conditions or lifestyle factors may help explain the findings

The researchers say the link between infertility and stroke risk might be explained by other conditions, like polycystic ovary syndrome (PCOS), which can both compromise fertility and may increase stroke risk. Suffering multiple pregnancy losses, meanwhile, can indicate a blood vessel problem that both compromises the placenta and puts women at risk of heart problems, other researchers have speculated.

The authors of the current study also noted that lifestyle factors like smoking can also contribute to both adverse pregnancy outcomes and stroke.

Ramsey, the chief of UT Health San Antonio's Division of Maternal-Fetal Medicine, said social determinants of health (like income, education, and healthcare access), as well as environmental factors, could also play a role in the findings.

But it's impossible to know from this research alone what, if anything, is going on, Ramsey said. Because the population studied was so big, "even minuscule differences can become significant statistically" without really meaning much for patient care.

He said more detailed studies following groups of patients over time are needed. "As we learn more about any clear defined relationship between pregnancy outcomes and long term risk for stroke, additional recommendations may emerge," he said.