Tobacco Harm Reduction: Not During Pregnancy (Revisited)

In May, I discussed a 2003 Swedish study reporting that pregnant women who use snus are at risk for slightly smaller babies, and have modestly elevated risks for premature delivery and preeclampsia (read the post here). Two new studies from Sweden also document that snus use has risks for the developing baby and should be avoided.

Both studies are based on over 600,000 pregnancies documented in the Swedish Medical Birth Register from 1999 to 2006, and both are authored by Anna-Karin Wikström and colleagues from the Karolinska Institute.

The first study, published in the British Journal of Obstetrics and Gynaecology (sic) (abstract here), examined the effect of tobacco use on the risk for very premature (less than 32 weeks) or moderately premature (32-26 weeks) births. It showed that snus users had a modestly elevated risk for a very premature birth (adjusted odds ratio, aOR = 1.38, 95% confidence interval = 1.04 – 1.83). The risk among light smokers (1-9 cigarettes per day) was 1.60 (CI = 1.42 – 1.81), and the risk among heavy smokers (10+ cigarettes) was 1.90 (CI = 1.61 – 2.25). The study also showed that snus users had an elevated risk for a moderately premature birth of 1.25 (CI = 1.12 – 1.40), which was intermediate between light smokers (aOR = 1.18, CI = 1.12 – 1.24) and heavy smokers (aOR = 1.45, CI = 1.35 – 1.56).

The second study, published in Epidemiology (abstract here ), examined the effect of tobacco use on the risk for stillbirth, which is the death of a baby during pregnancy. It showed that women who were snus users had a modestly elevated risk (aOR = 1.57, CI = 1.03 – 2.41), which was again intermediate between light smokers (aOR = 1.15, CI = 0.91 – 1.45) and heavy smokers (aOR = 1.85, CI = 1.39 – 2.46).

The study I discussed in May found that snus use was associated with preeclamsia, but Wikström and colleagues did not report a statistically significant elevated risk. In addition, they reported that snus users did not have elevated risks for bleeding or for infants who were small for their gestational age, both of which are seen in light and heavy smokers.

In general snus use is vastly safer than smoking, but pregnant women should refrain from using all tobacco products.

Tobacco Harm Reduction: Not During Pregnancy

One of the most common – and challenging – questions regarding tobacco harm reduction is whether it is applicable to pregnant women who smoke.

According to the 2004 Surgeon General’s report, smoking during pregnancy is associated with increased risks for premature delivery, low-birth-weight infants, and stillbirth. Smoking is also associated with increased risk for problems with the placenta (the organ that nourishes the fetus). These problems include growth of the placenta in the wrong location (placenta previa) and separation of the placenta from the mother’s uterus (placental abruption), both of which can place the mother and developing fetus at risk. Paradoxically, pregnant women who smoke have a significantly lower risk of preeclampsia (a form of high blood pressure). But the overall effect of smoking on the developing fetus is decidedly negative.

Can a pregnant smoker who switches to smokeless tobacco benefit her health and that of her developing baby? Only one scientific study has addressed this issue. It reported information on pregnancy outcomes among Swedish women who used snus or smoked, compared with nonusers of tobacco, and it was published in 2003 by a group of investigators from the Karolinska Institute in Sweden and the National Institute of Child Health and Human Development in the U.S. The abstract is available here.

In this study, tobacco users had smaller babies than nonusers, although the reductions were modest. The average baby weight for nonusers was 7 pounds 14 ounces; babies of snus users weighed 7 pounds 13 ounces, while light smokers (1-9 cigarettes per day) and heavier smokers (10+ cigarettes) had babies that weighed less (7 pounds 8 ounces and 7 pounds 6 ounces, respectively).

Women who used snus were more likely than nonusers to have a premature delivery (adjusted odds ratio, aOR = 1.79, 95% confidence interval = 1.27 – 2.52), which was similar to that of light (aOR = 1.56, CI = 1.33 – 1.83) and heavier smokers (aOR = 1.84, CI = 1.53 – 2.21).

This study confirmed that smoking is protective for preeclampsia. The aOR for light smokers was 0.71 (CI = 0.59 – 0.88), and heavier smokers’ risk was even less (aOR = 0.48, CI = 0.36 – 0.64). However, snus users had a somewhat elevated risk for preeclampsia (aOR = 1.58, CI = 1.09 – 2.27).

In summary, pregnant women who use snus are at risk for slightly smaller babies, and they also have modestly elevated risks for premature delivery and preeclampsia. Women who are pregnant should refrain from using all tobacco products.

Note: The original link to the research study abstract was wrong. It was corrected on September 7, 2010.