Apr. 13, 1999 By Victoria White
GAINESVILLE, Fla.---When a number of studies appeared during the 1980s and 1990s showing that cigarette smoking decreased a woman’s risk of certain diseases, scientists were stunned.
“The possibility that smoking could have a protective effect on pre- eclampsia, a sometimes life-threatening condition in pregnancy, was the exact opposite of what you would predict,” said Kathleen Shiverick a professor of pharmacology and therapeutics at the University of Florida College of Medicine. “And other studies had shown a surprising decrease in the rates of uterine cancer and endometriosis, which sometimes causes infertility.”
Those results prompted Shiverick and Dr. Carolyn Salafia, a professor of pathology and pediatrics at Columbia University College of Physicians and Surgeons, to undertake a comprehensive review of the medical literature. In articles to be published next month in the journal Placenta, they have concluded that the protective effects are more mirage than reality.
Pre-eclampsia, a sometimes fatal condition for mother and baby whose symptoms include high blood pressure, is less common among smokers because many of their troubled pregnancies are redirected into miscarriages, according to Salafia and Shiverick. When pregnancies do continue past the first trimester, there still can be problems.
“Smoking damages blood vessels,” Salafia said. “The vessels get so beaten up that they may not be able to respond to a damaged placenta with the high blood pressure characteristic of pre-eclampsia. This may ‘protect’ the mother. But the baby is still at risk because the placenta is damaged, and there is increased risk of pre-term birth and abruption, both of which can be lethal to the baby.”
And while endometriosis and uterine cancer may be less common among smokers, the reproductive system in such women is far from normal, leading to such problems as decreased production of eggs, difficulties becoming pregnant, higher rates of miscarriage and lower birth weights.
Smoking during pregnancy is responsible for an estimated $1.4 to $2 billion in health complications, according to the U.S. Centers for Disease Control. The good news, however, is that the rate of smoking among expectant mothers has declined in recent years, from 26 percent in 1990 to 13.6 percent in 1996.
The rates vary by age, with those 15 to 19 the most likely to be smokers. The figures also differ by race: Among pregnant white women in 1996, 16.9 percent reported smoking; for pregnant black women, the rate was 10.3 percent; and among Hispanics, just 4.3 percent said they smoked.
While smoking can cause some damage that is not reversible, Shiverick said: “To stop smoking is helpful at any point during pregnancy, and women who want to get pregnant are advised to stop smoking.”
Like others trying to break the addiction, some expectant mothers turn to nicotine patches for assistance. But animal studies have shown nicotine to be harmful to fetal brain development. Because of this, researchers who have explored the issue have suggested using nicotine gum instead or removing patches at night, Shiverick said.
“By removing patches at night or using the gum, at least there are breaks in the exposure to nicotine,” she said.
To try to understand the decreased risk of endometriosis associated with smoking, Shiverick experimented with laboratory-grown uterine tissue. In endometriosis, tissue that resembles the mucous membrane that lines the uterus grows in the wrong place, such as in the fallopian tubes, sometimes causing abnormal bleeding and scarring, and interfering with fertility. Shiverick found that a toxin in cigarette smoke, benzo(a)pyrene, actually inhibited the growth of cells that could migrate and develop into endometriosis.
“But if the chemical has the same inhibitory effect on the growth of normal uterine tissue, this would not be favorable for establishing pregnancy,” said Shiverick, noting that she has not yet conducted such studies. “This may be a good profile for reducing the risk of endometriosis, but this is not a normal uterus.”
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