Hypertensive disorders of pregnancy (HDP) more than double the risk of a later cardiovascular event in women, according to new Australian research.

Using data from the Maternal and Child Health Registry, the study of 528,000 women who had pregnancies in NSW between 2002 and 2016 found 10.3% of women had pre-eclampsia, eclampsia or gestational hypertension.

Women with HDP had a 10-year estimated risk of a cardiovascular event (hospitalisation or death due to ischaemic heart disease, stroke or hypertensive disease) of 5.5 per 1,000 compared to just 2.1 per 1,000 in women without HDP.

Maternal age increased the risk of a cardiovascular event in both groups, but to a greater extent in those with HDP.

In women aged 35 years and over, the risk of a cardiovascular event was 10.4 per 1,000 in the HDP group versus 4.0 per 1,000 in the non-HDP group.

Smoking tripled the risk of a cardiovascular event in those with HDP (9.0 v 3.0 per 1,000).

“The presence of both diabetes and HDP resulted in a more than doubling of the risk of a fatal or non-fatal cardiovascular event as compared with diabetes alone (10.9 vs 3.6 per 1000 risk),” the study said.

“Similarly, the coexistence of HDP and an SGA [small for gestational age] fetus more than doubled the risk of a cardiovascular event (6.2 vs 2.3 per 1000).”

Early-onset HDP (≤34 weeks’ gestation) was the most powerful risk factor, with a 15.9 per 1,000 risk of fatal or non-fatal cardiovascular event at 10 years.

The study, published in Heart, concluded that HDP conferred an increased relative risk of maternal CVD or death to a greater magnitude than that seen with the traditional risk factors.

For example, smoking alone conferred less than a doubling of CVD risk.

“While estimated absolute risk was low in these young women, the relative risk, as compared with matched women with an unexposed pregnancy, was dramatic: a more than doubling of the risk of a cardiovascular event or death in those with late-onset HDP and almost five times the risk following early-onset disease.”

And there was an alarming synergistic effect between all risk factors.

“The combination of early-onset HDP, gestational diabetes and smoking resulted in a relative risk of almost 50 for a maternal cardiovascular event.”

“These data highlight the importance of ensuring systematic postpartum cardiovascular follow-up with a focus on addressing modifiable risk factors, such as smoking,” said the authors, led by cardiologist Dr Clare Arnott of the Royal Prince Alfred Hospital, Sydney.

They also noted that women with HDP should not be overlooked by researchers as their increased CVD risk was of a higher order of magnitude than that observed with smoking.

“Given that more than 80% of HDP is late onset, these women should be identified as an important research and clinical priority, with an opportunity to alter the cardiovascular trajectory of a large population of women.”

The authors concluded that clear guidance on postpartum follow-up for at-risk women needs to be urgently developed and implemented.