NEW YORK (Reuters Health) - Women who develop high blood pressure during pregnancy are more likely to gain weight over the following two decades than women who have uncomplicated pregnancies, a new study shows.

The findings suggest it may be possible to identify women at risk of future obesity and related health disorders "at a time when they might be particularly receptive to initiatives aimed at reducing this risk," Dr. Leonie K. Callaway of the Royal Brisbane and Women's Hospital in Queensland, Australia and colleagues write.

While women who are obese face a greater risk of developing high blood pressure (hypertension) during pregnancy, most women who develop complications such as hypertension or pre-eclampsia are not overweight, Callaway and her team point out in the American Journal of Epidemiology.

Women who develop hypertensive disorders of pregnancy are more likely to have later health problems such as heart disease, hypertension or blood clots.

The researchers hypothesized that women with hypertensive disorders of pregnancy, whether or not they were obese when they became pregnant, are more likely to become overweight, which could help explain their increased risk of these health problems.

Callaway's group looked at data for 3572 women who delivered infants at a local public hospital between 1981 and 1984, and were then followed for 21 years. Among the 8.9 percent of these women who developed a hypertensive disorder of pregnancy, 73.3 percent were of normal weight when they became pregnant, as measured by body mass index (BMI).

BMI is the ratio of height to weight commonly used to determine which weight range an individual falls into. A BMI between 18.5 and 24.9 is considered normal; less than 18.5 is underweight; between 25 and 29.9 is overweight; and greater than 30 is obese. Individuals who are 100 pounds or more over their ideal weight or who have a BMI of 40 or higher are considered morbidly obese.

In the following 21 years, the researchers found that the BMI of women with hypertensive disorders of pregnancy was an average of 1.35 greater than the women who did not develop these pregnancy complications.

Women with hypertensive pregnancy complications were also 59 percent more likely than those without these complications to have a BMI increase of 5 or greater in the subsequent decades.

These finding are "important because the propensity to gain weight might partly contribute to the excess burden of chronic disease that these women are known to develop," the researchers write. Further studies are needed, they conclude, to determine if helping these women control their weight over time will prevent them from developing these health problems.

SOURCE: American Journal of Epidemiology, August 15, 2007.