"We know these women are at risk, but no one really knows if there (is) anything to do about it," said Dr. Baha Sibai, a professor of obstetrics and gynaecology.
About one in 300 women aged 20 to 39 have strokes in the US each year, according to the American Heart Association.
The researchers found that women aged 15 to 40 had about a one in 150 chance of having a stroke within six years, if they had high blood pressure during pregnancy. If a woman had both high blood pressure and a premature delivery, this jumped to about a one in 110 chance.
There was also a one in 225 chance of having a stroke if the baby was premature, even if the mother didn't have high blood pressure while she was pregnant.
The researchers looked at two conditions that involve high blood pressure during pregnancy. One, gestational hypertension, is blood pressure greater than 140/90 after the 20th week of pregnancy.
Healthy blood pressure is 120/80 or lower.
About 20% of women go on to develop the second condition, preeclampsia. That life-threatening disorder involves high blood pressure during the second half of pregnancy and protein in the urine. It affects about 5% of pregnant women.
Doctors have known about the link between high blood pressure during pregnancy and stroke for about 30 years, said Sibai.
These women should be followed more closely after they have their babies, to see if more attention to their health would reduce the risk of stroke later in life.
What this study added was a look at the medical records of about 5800 women, about 1000 of who had high blood pressure during pregnancy.
Within six years of having a baby, 21 of the women with high blood pressure had a stroke. In women who did not have high blood pressure while they were pregnant, 40 had a stroke in the same time period.
To reduce the risk of stroke keep fit, eat sensibly and don't smoke.
Did you have high blood pressure when you were pregnant?