Previous research has shown that women who experience complications during pregnancy face roughly twice the risk of dying prematurely from cardiovascular disease.
"Cardiovascular disease in women is underrecognized and undertreated and as such pregnancy complications have been proposed as a way to identify at-risk women. Our earlier work found that a woman's risk of premature cardiovascular mortality increases with the number of complicated pregnancies. However, many studies and guidelines still only ask whether a woman has ever had a complication," says Aditi Singh, PhD candidate at the Department of Global Public Health and Primary Care, University of Bergen, and a general practitioner in Askvoll municipality.
Together with colleagues at the National Institute of Environmental Health Sciences, the Stanford University School of Medicine, and the University of Bergen, Singh examined how the number, sequence and type of pregnancy complications across a woman's reproductive history were associated with premature cardiovascular death.
"We investigated whether cardiovascular risk varied according to the total number of pregnancies a woman had and whether complications occurred in a first or later pregnancy," says Singh.
Singh and colleagues linked data from the Medical Birth Registry of Norway and the Cause of Death Registry between 1967 and 2020. They studied cardiovascular death before age 70 among around one million women with complete pregnancy histories and examined six pregnancy complications: preeclampsia, gestational hypertension, placental abruption, preterm delivery, perinatal loss and small-for-gestational-age birth, both individually and as a composite measure.
Two women, one complication, very different cardiovascular risks
The study found that women whose first pregnancy was complicated and had no further pregnancies had the highest risk, around 3.3 times that of women with two or more uncomplicated pregnancies. Women who had a complication in their first pregnancy and another complication in a later pregnancy faced a 2.4-fold higher risk, regardless of whether the later complication was the same type or a different type. "This is something often missed in studies that focus on a single pregnancy complication at a time," says Singh.
Women whose only complication came in a later pregnancy had a moderately raised risk, about 1.7 times higher, while women whose first pregnancy was complicated but whose later pregnancies were not had the lowest risk, about 1.4 times higher. Even women who never had a complication but who had only one pregnancy showed a raised risk, about 1.8 times higher compared with women who had two or more uncomplicated pregnancies.
"Two women who both had a pregnancy complication may face very different long-term cardiovascular risks. Such differences are not apparent when women are grouped simply according to whether they have ever had a pregnancy complication," says Singh.
Grouping women simply by whether they had ever had a pregnancy complication yielded a 1.7 times higher risk of premature cardiovascular death compared with women who never had complications. "Roughly one-third of women had substantially higher risks than suggested by the simple yes-or-no classification, while the remaining two-thirds had lower risks," says Singh.
Implications for women's cardiovascular health
"As with other observational studies, it is difficult to draw firm conclusions about causality," says Singh. She notes that a woman's pregnancy history reflects a combination of biological, medical, and social factors that shape both reproductive decisions and long-term health. It remains unclear whether pregnancy complications directly cause cardiovascular disease, or whether they instead reflect underlying poor cardiovascular health that becomes apparent during pregnancy.
"But regardless of the underlying mechanism, a woman's pregnancy history still carries valuable information about her future risk, and that is something we can act on now, while further research works out exactly why these patterns exist. Identifying and following up these women is an important area for future work."
