Pregnant women who use a smokeless form of tobacco known as “snus” may have a risk of stillbirth on par with women who smoke cigarettes, a large study of Swedish women suggests.

The findings, say experts, should serve as a warning to women who are or may become pregnant that snus is not a “safe” alternative to cigarettes.

Snus, also called moist snuff, is different from other smokeless tobacco products because it is “spitless” and has lower levels of toxins called tobacco-specific nitrosamines.

Snus is generally thought to be less harmful than cigarettes as far as the risks of heart disease and cancer, and the product has been advocated as a “socially acceptable” way for smokers to get their nicotine fix - and as a way to help them cut down on cigarettes.

Snus originated in Sweden and is still mainly used there. But in the past few years tobacco makers have been test-marketing their own snus products based on the traditional Swedish one. Brands such as Camel Snus and Marlboro Snus are now available in the U.S.

Smoking during pregnancy is well-known to carry risks, including elevated odds of miscarriage, low birth weight and stillbirth.

Much less has been known about the potential harms of using snus during pregnancy. But a study published earlier this year by the research group behind the new study found that women who used snus during pregnancy had a higher risk of preterm delivery than those who used no tobacco products.

For the current study, published in the journal Epidemiology, the Swedish team used a national birth register with information on nearly 611,000 women who were pregnant between 1999 and 2006. Of these, 58,502 were tobacco smokers and 7,629 used snus.

Overall, 1,926 of the women in the register - or about 0.3 percent - had a stillbirth. (Stillbirth generally refers to a pregnancy loss after the 20th week; but in this database, it was defined as a pregnancy loss after at the 28th week or later.)

The study found that women who reported using snus during pregnancy had a 60 percent higher risk of suffering a stillbirth than women who used no tobacco products. The risk was 40 percent higher for light smokers, and for heavy smokers it was more than double that of non-users of tobacco.

Among the women who reported using snus, 0.5 percent (40 women) suffered a stillbirth; that compared with just under 0.3 percent (1,386 women out of more than 500,000) of those who used no tobacco products during pregnancy.

Of the 41,488 women considered light smokers - nine or fewer cigarettes per day - 0.4 percent (172) had a stillbirth. And among the 17,000 women who smoked more heavily, the stillbirth rate was 0.7 percent (120).

Although snus may appeal to pregnant women who are trying to avoid cigarettes, “using moist snuff is not a safe way to quit smoking when you are pregnant,” lead researcher Dr. Anna-Karin Wikstrom, of Karolinska University Hospital Solna in Sweden, told Reuters Health in an e-mail.

Dr. Gregory N. Connolly, director of the Tobacco Control Research Program at the Harvard School of Public Health, agreed.

“This study is chilling, particularly in light of the expanding marketing of these products,” said Connolly, who was not involved in the research.

He noted that the new snus products being marketed by U.S. tobacco companies appear to have lower levels of nicotine than Swedish snus - which may matter, as nicotine may be at least partly responsible for the increased stillbirth risk.

“These findings may be applicable to the U.S.,” Connolly said, “but one has to take into account the differences in (products’) nicotine levels.”

The mechanism by which snus might affect stillbirth is not fully clear, according to both Connolly and Wikstrom. Research has suggested that smoking contributes to stillbirth mainly by impairing fetal growth, which may be a product of the carbon monoxide, nicotine and other toxins in tobacco smoke. Nicotine is the component found in both tobacco smoke and snus.

“One would think nicotine probably has an important role,” Connolly said.

The study has limitations. Connolly noted that women were asked only whether they used snus or not, and not how often. It would have been helpful, he said, to see whether heavier users had a higher stillbirth risk than light users (as was seen among cigarette smokers); such a “dose-response” relationship would provide stronger evidence that the snus itself was the reason for the increased stillbirth risk.

However, Connolly said he does not think that takes away from the findings.

“As studies like this and others come out,” Connolly said, “I would expect the FDA will take action to help assure that pregnant women are protected from exposure to smokeless tobacco products.”

R.J. Reynolds Tobacco, maker of Camel Snus, did not comment directly on the study findings. But spokesman David Howard said in an e-mail that the company “agrees that women should not use snus or any tobacco product during pregnancy.”

Altria/Phillip Morris USA, which markets Marlboro Snus, also made no specific comment on the findings. In an e-mail, a spokesman pointed to the company’s general position that people should rely on health warnings from public health authorities in deciding whether to use smokeless tobacco products.

SOURCE:  Epidemiology, online August 27, 2010.