Obesity doubles the risk of high blood pressure in pregnancy

Years of gradual weight gain more than doubles the risk of hypertensive disorders in pregnancy, regardless of whether the woman's body mass index (BMI) was initially categorized as healthy or overweight, according to a new analysis.

Though health experts have focused on BMI in the last few decades, it is really only valid for population studies, not individuals, so the authors state that a BMI of over 30 at the time of pregnancy was the leading avoidable risk factor for hypertensive disorders. They drew their conclusion by tracking the weight and pregnancy health of 2914 Australian women born between 1973 and 1978 as part of the Women's Health Australia study (also known as the Australian Longitudinal Study on Women's Health) over a 13 year period.

In the years leading up to pregnancy, women with moderate to high annual weight gains of more than 2.5 per cent of their body weight had a 2.3 times greater risk of developinghypertensive disorders than those whose weight remained stable. Small annual weight gains of 1.5 to 2.5 percent still resulted in a 1.7 times higher risk of developing HDP. Meanwhile, women who lost more than 1.5 percent of body weight between the average ages of 20 to 24 years were 46 percent less likely to develop hypertensive disorders. For a 70 kilogram woman, a small weight gain of 1.5 to 2.5 percent of their body weight is in the range of 1.05 to 1.75 kg per year. 

Hypertensive disorders such as high blood pressure and pre-eclampsia were common complications for pregnant women and led to an increased risk of chronic high blood pressure in later life.