A database analysis found that younger women are at an increased risk of stroke during pregnancy, although older women do not have an increased risk of stroke. The researchers considered older women as those who were at least 35 years old.

They noted that 18 percent of strokes in women younger than 35 years old were associated with pregnancy, whereas 1.4 percent of strokes in women who were at least 35 years old were associated with pregnancy.

Lead researcher Eliza C. Miller, MD, of Columbia University in New York, and colleagues published their results online Oct. 24 in JAMA Neurology.

“We have been warning older women that pregnancy may increase their risk of stroke, but this study shows that their stroke risk appears similar to women of the same age who are not pregnant,” Miller said in a news release. “But in women under 35, pregnancy significantly increased the risk of stroke. In fact, one in five strokes in women from that age group were related to pregnancy. We need more research to better understand the causes of pregnancy-associated stroke, so that we can identify young women at the highest risk and prevent these devastating events.”

Approximately 34 of 100,000 women have pregnancy-associated stroke (PAS), according to the researchers, who added that the incidence has increased in recent years.

For this analysis, they used the New York State Department of Health inpatient database and population data and identified 19,146 women who were hospitalized for stroke from 2003 to 2012. Of the women, 797 were pregnant or postpartum.

For women from 12 to 24 years old, the incidence of PAS was 14 per 100,000 pregnant/postpartum women and the incidence of nonpregnancy-associated stroke (NPAS) was 6.4 per 100,000 nonpregnant women. For women from 25 to 34 years old, the incidences were 21.1 per 100,000 and 13.5 per 100,000, respectively.

For women from 35 to 44 years old, the incidence of PAS was 33 per 100,000 pregnant/postpartum women and the incidence of NPAS was 31 per 100,000 nonpregnant women. For women from 45 to 55 years old, the incidences were 46.9 per 100,000 and 73.7 per 100,000, respectively.

Women in the NPAS group were older, more likely to be white and more likely to be uninsured compared with the PAS group.

The researchers found that PAS accounted for 15 percent of strokes in women from 12 to 24 years old, 20 percent of strokes in women from 25 to 34 years old, 5 percent of strokes in women from 35 to 44 years old and 0.05 percent of strokes in women from 45 to 55 years old.

Of the women with PAS, 33.1 percent of strokes occurred antepartum, 22.3 percent occurred during the delivery hospitalization without specification of antepartum or post partum and 44.5 percent occurred post partum. Of the strokes that occurred postpartum, 70.1 percent occurred after discharge from the hospital following delivery.

In addition, 54.1 percent of the women with PAS underwent cesarean delivery, 32.5 percent had hypertensive disorders of pregnancy and 14.7 percent had an infection when admitted to the hospital.

A multivariable analysis found that women with PAS were significantly less likely than women with NPAS to have preexisting hypertension, diabetes, cancer, HIV and alcohol abuse.

The mortality rates were 6.4 percent in the PAS group and 13.1 percent in the NPAS group, which was a statistically significant difference. Most women in the PAS group who died were younger than 35 years old, whereas most women who died in the NPAS group were 35 years old or older.

The researchers cited a few limitations of the study, including that the billing data lacked specificity with regard to PAS. They also could not determine the exact timing of PAS in many women and did not account for some risk factors and medication effects.

“These results have potential implications for research aimed at better characterizing and preventing PAS and clinically in terms of counseling patients,” the researchers wrote. “Although older women have an increased risk of many pregnancy complications, a higher risk of stroke may not be one of them. Our results should be interpreted with caution and regarded primarily as hypothesis generating; more research is needed to investigate why younger women may have an increased risk of PAS.”