Women with slightly elevated blood pressure before they get pregnant may have an increased risk of miscarriage, even if they’re not diagnosed with hypertension.

Researchers examined data on 1,228 women with at least one previous pregnancy loss who were trying to conceive. Out of the 797 participants who became pregnant during the study, 188, or about 24 percent, had a miscarriage.

Even when their blood pressure was in a healthy range before pregnancy, each 10 mmHg increase in systolic blood pressure was associated with an 8 percent higher risk of miscarriage. Each 10 mmHg increase in diastolic blood pressure was associated with an 18 percent greater chance of miscarriage.

The American Heart Association defines hypertension, or high blood pressure, as a systolic reading of 130 mmHg or higher, and diastolic readings of 80 mmHg or higher.

Systolic pressure reflects the pressure blood exerts against artery walls when the heart beats. Diastolic pressure indicates the pressure between beats.