In a study of nearly 1,300 Japanese women with a past pregnancy, researchers found that those who smoked heavily early in pregnancy were more than twice as likely as non-smokers to suffer a miscarriage in the first trimester.
There are many reasons for women to quit smoking before becoming pregnant. The habit has been linked to increased risks of stillbirth, preterm delivery and low birthweight.
But studies so far have come to conflicting conclusions as to whether smoking might contribute to miscarriage risk.
These latest findings, reported in the journal Human Reproduction, support a connection.
For the study, researchers led by Dr. Sachiko Baba of Osaka University reviewed the records of 430 women who'd suffered a first-trimester miscarriage. They compared each woman with two others the same age who had given birth that same year.
Overall, the researchers found, women who smoked heavily during pregnancy -- at least 20 cigarettes per day -- were more than twice as likely as the non-smokers to have a miscarriage.
Seven percent (32) of the 430 women who suffered a miscarriage smoked that amount, versus four percent (36) of the 860 women who delivered a