A woman’s risk of atrial fibrillation — an abnormal heart rhythm — rises with each pregnancy, up to a nearly 50 percent increased risk with six or more pregnancies, according to the results from one study.
“There’s something about pregnancy itself that predisposes women toward this risk,” said lead author Dr. Jorge Wong. He’s a cardiologist with the Population Health Research Institute at McMaster University in Hamilton, Ontario.
Neither of these studies proves a direct cause-and-effect relationship between pregnancy and heart problems, both teams of researchers noted.
For the heart rhythm report, researchers reviewed data from 34,639 participants in the Women’s Health Study, an ongoing project conducted by Harvard Medical School and Brigham and Women’s Hospital in Boston.
After an average 20 years’ follow-up, researchers found that 1,532 cases of atrial fibrillation had developed among the women. Atrial fibrillation is an irregular heart beat that increases the risk of stroke or heart failure.
Analysis revealed that women with a single pregnancy had a 15 percent increased risk of atrial fibrillation compared to women who never were pregnant, after researchers controlled for other heart risk factors.
Two or three pregnancies were associated with a 20 percent increased risk of atrial fibrillation, four to five pregnancies with a 36 percent increased risk, and six or more with a 46 percent increased risk, the researchers said.
Pregnancy causes many potentially damaging changes in a woman’s body, and researchers speculate that additional pregnancies might expose women to more injury.
“For some unknown clear reason, these add up to developing atrial fibrillation later in life,” Wong said.
“There are also documented cardiac changes that happen due to pregnancy which are always thought to completely resolve at the end of the pregnancy,” Wong added. “But it’s also been speculated that in women who have multiple pregnancies, these structural changes may take longer to resolve.”