University of Queensland research has shown that gradual weight gain during a woman's reproductive years can more than double her risk of hypertensive disorders during pregnancy.
School of Public Health researcher Akilew Adane said this and other maternal health research added to the evidence that parents and clinicians should think of pre-pregnancy health across the entire reproductive stage of women's lives, "not just the year before starting a family".
Mr Adane said the increased risk due to weight change and occurred regardless of whether the woman's body mass index (BMI) was initially categorized as healthy or overweight.
He said 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.
"High blood pressure in pregnancy can progress to pre-eclampsia, a potentially fatal complication and one of the leading causes of pre-term birth and low birth weight due to intra-uterine growth restriction," Mr Adane said.
"The leading avoidable risk factor for hypertensive disorders is having a body mass index (BMI) over 30 when you become pregnant."
Very little was known about the relationship between hypertensive disorders and weight changes in the years leading up to pregnancy, so researchers set out to investigate the links.
For 13 years they tracked 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).
"We found that women who were obese just prior to pregnancy tripled their risk of developing hypertensive disorders compared to women in the healthy BMI category," Mr Adane said.
"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 developing HDP than those whose weight remained stable.
"Small annual weight gains of 1.5 to 2.5 per cent still resulted in a 1.7 times higher risk of developing HDP.
Mr Adane said women who lost more than 1.5 per cent of body weight between the average ages of 20 to 24 years were 46 per cent less likely to develop hypertensive disorders.
For a 70kg woman, a small weight gain of 1.5 to 2.5 per cent of their body weight is in the range of 1.05 to 1.75 kg per year.
"It's easy to overlook a kilogram or two per year of gradual weight change but it does have long-term consequences," Mr Adane said.
"Weight loss, if necessary, and weight stabilization in a healthy BMI range is important at any time."