Women who have premature babies are more likely than other mothers to develop heart disease later in life, even if they did not have any risk factors for cardiovascular problems before pregnancy, a recent study suggests.
Compared to women who delivered their first babies after 37 weeks, first-time mothers of infants born earlier are 40 per cent more likely to develop heart disease, the study found. With extremely preterm infants born before 32 weeks, first-time mothers had twice the later heart risk.
No more than 21 per cent of the increased risk of cardiovascular disease for mothers of premature babies could be explained by weight gain, hypertension, high cholesterol or diabetes that women developed after they had their first baby, researchers report in the journal Circulation.
The rest is unexplained and requires more research, but suggests that preterm delivery should be added to the list of women's risk factors for future heart disease, the study team writes.
Women who deliver a preterm infant have an early warning signal for their future cardiovascular health
"Women who deliver a preterm infant have an early warning signal for their future cardiovascular health," said lead study author Lauren Tanz of the Harvard TH Chan School of Public Health and Brigham and Women's Hospital in Boston.
"They may want to take special care with their hearts by adopting a heart healthy diet and lifestyle, including maintaining a healthy body weight, exercising, and not smoking," Ms Tanz added.
For the study, researchers examined data on more than 70,000 US mothers, following half of them for at least 32 years.
The data was collected starting in 1989 as part of a long-term health study of nurses that included periodic surveys on medical conditions, diet, exercise, smoking, medication use and reproductive history.
Overall, almost nine per cent of the women delivered preterm babies in their first pregnancy. Roughly two per cent delivered very preterm, or before 32 weeks, while about seven per cent delivered during weeks 32 to 36 of pregnancy.
Women who delivered preterm were more likely to be overweight or obese, have hypertension or high cholesterol or a family history of cardiovascular disease before they gave birth.
During the study, researchers observed 949 heart attacks and 455 strokes.
The increased risk seen among mothers of preemies translates to higher likelihoods of dying from one of those events, the researchers calculate. While 31 per cent of women in general will die from cardiovascular disease, that figure rises to 36 per cent for those who deliver three to seven weeks early and up to 60 per cent for women who deliver eight or more weeks too soon.
Limitations of the study include the reliance on women to accurately recall and report how long pregnancy lasted and the lack of data to explore differences between spontaneous versus induced preterm deliveries, the authors note.
Still, the study is the largest to date to establish a link between preterm delivery and a future risk of heart disease for women, said Wayne Franklin of the Texas Children's Hospital and Baylor College of Medicine in Houston.
We think that pregnancy acts as a stress that worsens a woman's cardiovascular disease risk
"We think that pregnancy acts as a stress that worsens a woman's cardiovascular disease risk," Dr Franklin, who was not involved in the study, said.
Causes of premature birth like infection and inflammation are also well-known risk factors for heart disease, Dr Franklin said.
"Early delivery itself doesn't necessarily lead to the increased cardiovascular risk, but the process that leads to the early delivery is the same process that leads to heart attacks and strokes - and that's the culprit," Dr Franklin added.
Mothers of preemies - especially before 32 weeks - should have heart health checkups at least once a year and try to minimise their risk of cardiovascular disease by keeping blood pressure, cholesterol levels and blood sugar within a healthy rage, said Kaberi Dasgupta of McGill University in Montreal.
"These are the things we can do something about, even if they may not fully explain the relationship between preterm delivery and heart disease and stroke later in life," Ms Dasgupta, who wasn't involved in the study, added.