BOSTON — Two researchers have produced startling numbers to back up the long-held belief that smoking during pregnancy can prove fatal to fetuses and infants.
Mothers who smoke cause the deaths of about 5,600 babies and cause between 19,000 and 141,000 miscarriages in America annually, said Joseph DiFranza and Robert Lew, who reviewed nearly 100 studies conducted over a 40-year period.
As many as 26,000 newborn babies are admitted to intensive-care units each year because of low birth weight caused by smoking, the researchers estimate in this month's Journal of Family Practice.
While earlier studies have examined the risks associated with smoking during pregnancy, "no one had ever tried to calculate . . . the numbers of children actually harmed," said DiFranza, an associate professor of family and community medicine at the University of Massachusetts Medical Center in Worcester.
The doctors said they reached their numbers by using estimated percentages and the actual numbers of women who get pregnant each year and those expecting who smoke.
Dr. Arnold Platzker, head of neonatology at Children's Hospital in Los Angeles and a professor of pediatrics at the University of Southern California, said the figures were "totally believable."
The researchers said tobacco use by pregnant women results in 1,900 annual cases of sudden infant death syndrome, in which apparently healthy infants are found dead.
An additional 3,700 children die each year by the age of 1 month of complications caused by tobacco smoke during pregnancy, the researchers said.
Studies have found that between 20% and 62% of pregnancies end in spontaneous abortion, with most miscarriages occurring before a woman knows she is pregnant.
The researchers' "best-case" estimate of 19,000 tobacco-induced miscarriages uses the lowest estimate of the proportion of pregnant women who smoke, and includes only those pregnancies and miscarriages that are recognized by women and their doctors. The "worst-case" figure of 141,000 uses the highest estimate of smoking prevalence, and includes miscarriages that occur before a woman realizes she is pregnant.