TUESDAY, July 13, 2021 (HealthDay News) -- Women who use electronic cigarettes during pregnancy may be at heightened risk of having an underweight or preterm baby, a new study suggests.
The study of more than 79,000 U.S. mothers found that when women regularly used e-cigarettes late in pregnancy, their babies' risk of low birth weight rose.
Of women who "vaped" but did not smoke standard cigarettes, just under 11% had an underweight baby. That compared with around 6% of women who avoided all cigarettes.
Experts said the findings underscore a familiar public health warning: E-cigarettes are not a "safe alternative" to smoking.
"The take-home message is that it's best to abstain from e-cigarettes while you're pregnant, if you can," said lead researcher Annette Regan, an assistant professor at the University of California, Los Angeles.
The dangers of smoking during pregnancy are well known, and include increased risks of preterm birth, low birth weight and sudden infant death syndrome.
The question is whether e-cigarettes can carry similar hazards. The battery-powered devices work by heating a liquid, which creates a "vapor" that is inhaled. That allows users to avoid tobacco smoke, but they are still breathing in nicotine.
"And nicotine is acknowledged as a developmental toxicant," Regan said.
Beyond the nicotine content, e-cigarettes have a base liquid of glycerin and propylene glycol -- substances widely used in consumer products, from food additives to cosmetics.
But in e-cigarettes, they are vaporized and inhaled. And that may be a problem, according to Mark Olfert, an associate professor at West Virginia University School of Medicine. He wasn't part of the new study.
In animal research, Olfert has found that e-cigarette vapor causes the same kind of stiffened arteries that tobacco smoke does. And it appears to be an effect of the heated chemicals in the liquids.
If a pregnant woman vapes, one concern is that any such blood vessel effects could impair blood flow to the womb, Olfert said.
But his team found another red flag in a study published earlier this year: When pregnant animals are exposed to e-cigarette vapor, their offspring show impaired dilation in their own blood vessels.
Human studies, of course, are different. And since many people who vape also smoke, it takes a large study to suss out a correlation between exclusive e-cigarette use and a bad pregnancy outcome.
So size is a strength of the new study, according to Olfert.
"It's nice to see a larger study like this," he said. "And there's certainly animal data to back it up."
The findings -- published in the July issue of the journal Obstetrics & Gynecology -- are based on U.S. women who were part of a federal government study of mother-child health. All were surveyed shortly after giving birth.
Only about 1% said they had used e-cigarettes during the third trimester of pregnancy, and the majority of those also smoked cigarettes. But of women who said they had only vaped, about 12% had a preterm birth, and almost 11% had a low-birthweight baby.
Those figures were roughly 8% and 6% among women who had neither smoked nor vaped.
When the researchers dug deeper, they found the increased risk was limited to women who'd used e-cigarettes daily.
"This study confirms what was already suspected from prior studies," said Beth Conover, a senior genetic counselor and director of MotherToBaby Nebraska.
MotherToBaby is a national nonprofit service that provides information on the effects of various exposures during pregnancy.
Conover said it's challenging to study the health effects of e-cigarettes, partly because the products are not well-regulated.
"Some contain a lot of nicotine, while others very little," she said. "They often have other substances added to them, including preservatives and flavorings. Most of these agents have not been studied in pregnancy."
She agreed that the safest course is for pregnant women to avoid vaping.
Of course, nicotine is highly addictive, and some smokers who become pregnant might turn to e-cigarettes as an aid in quitting.
"Unfortunately," Conover said, "e-cigarettes are not a proven way to quit smoking."
She suggested women talk to their health care provider about tactics for quitting, or try free services like the U.S. Centers for Disease Control and Prevention's quit line (800-QUIT-NOW).
Ideally, women can do that when planning a pregnancy, but many pregnancies are unplanned. Regan encouraged women to talk to their doctor about smoking cessation at their first prenatal visit.
MotherToBaby has a fact sheet on e-cigarettes.
SOURCES: Annette Regan, PhD, MPH, assistant professor, epidemiology, University of California, Los Angeles Fielding School of Public Health; Mark Olfert, PhD, associate professor, Department of Physiology and Pharmacology, West Virginia University School of Medicine, Morgantown; Beth Conover, MS, APRN, director, MotherToBaby Nebraska, and assistant professor, University of Nebraska Medical Center, Omaha; Obstetrics & Gynecology, July 2021