Women with slightly elevated blood pressure during pregnancy could be more likely to develop so-called metabolic syndrome later, Chinese researchers say.

Metabolic syndrome - a combination of traits and symptoms such as abdominal fat and high blood sugar - is a strong predictor of heart disease and diabetes. So blood pressure at the high end of normal in pregnancy could be an early warning sign, according to the study authors.

"The optimal blood pressure levels in pregnant women remain an open question," said lead author Dr. Jian-Min Niu of Guangdong Women and Children Hospital in Guangzhou.

In general, healthy blood pressure usually falls at or below 120/80 mmHg, Niu said. The threshold for high blood pressure, or hypertension, is 140/90 or greater. The range between "healthy" and "high" blood pressure is sometimes called prehypertension because readings at the high end of normal may be a stage on the way to full-fledged hypertension.

"In many countries, every pregnant woman has at least 10 routine (prenatal) checkups," Niu told Reuters Health by email. "However, they will not be informed of risk unless the blood pressure level is at or greater than 140/90 mmHg."

The researchers studied 506 pregnant women with no history of high blood pressure or symptoms of diabetes, measuring their blood pressure, weight and other health metrics several times during pregnancy and for up to a year and a half after they gave birth.

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For about one third of the women, blood pressure remained in the low-normal range throughout pregnancy. Half the women remained in the mid-normal range and 13 percent developed high-normal blood pressure.

Of the 309 women who completed all the follow-up tests, 35 developed metabolic syndrome, that is, at least three of the following: waist circumference of 35 inches or greater, elevated triglycerides, low levels of high-density lipoprotein (HDL) cholesterol, blood pressure of 135/85 or higher and elevated blood sugar.

Women with high-normal blood pressure in the last months of pregnancy were more than six times as likely as those in the low-normal group to develop metabolic syndrome, according to the results in the journal Hypertension.

"I would expect that this pattern also predicts other related factors such as cardiovascular outcomes and events," said Pal R. Romundstad, of the Public Health and General Practice department at the Norwegian University of Science and Technology in Trondheim, who was not part of the study.

Maintaining a healthy weight before and during pregnancy can help reduce the risk of prehypertension or metabolic syndrome, Niu said.

"Postpartum follow-up is very important, because pregnancy is a 'stress test' that may unmask predisposition to future cardiovascular diseases," Niu said. "Based on our study, those who have prehypertension should be monitored with caution after delivery as well."