Vaping while pregnant: What we know

A flurry of studies published since the outbreak of the 2019 "vaping crisis" have tried to measure the health impact of e-cigarettes on pregnant women and their newborn babies. And for good reason: In the UK, estimates suggest that up to 23%of pregnant smokers and ex-smokers vape nicotine.

But the results of research so far have been mixed.

In March 2023, the authors of an article in the journal Toxic had looked at "existing evidence and knowledge gaps on the risks of vaping during pregnancy." In summary, the authors advised against vaping in pregnancy because of the potential presence of unknown toxins in vape juice. A studypublished in the journal Developmental Biology in September 2023 found that vaping could harm fetal lung and bone development in mice. But then another study published in the JAMA Network found no association between vaping in late pregnancy and low birth weight.

Now, a new study published in January in the journal Addiction seems to support the JAMA conclusion, but goes one further to say that vaping nicotine in pregnancy is "not associated with any adverse effects in mothers or their babies."

But researchers DW contacted highlighted shortcomings in the latest study, which may help illustrate a more general difficulty in studying vaping in pregnancy.

First, let's look at the new study in more detail.

How the latest research on vaping in pregnancy was done

For the study in Addiction, researchers recruited around 1,100 pregnant women who smoked daily in England and Scotland, but who were seeking help with quitting.

All participants smoked cigarettes through their first trimester. Researchers provided the women with both e-cigarettes and Nicorette patches — a branded nicotine replacement product, used by smokers to help them get off cigarettes.

At the start of the trial, they tested the womens' salivary cotinine levels. Cotinine is an alkaloid found in tobacco and the main metabolite of nicotine. It is used as one of the primary biomarkers for tobacco smoke exposure.

At the end of the pregnancy, researchers tested participants' saliva again, gathered any reports of respiratory symptoms since starting treatment and tracked the babies' birth weights.

Authors put participants into three categories based on their self-reported smoking behavior over the course of the pregnancy: Those who said they had stopped smoking cigarettes entirely, those who said they had reduced their cigarette consumption by at least 50% and those who said they had used nicotine products and continued smoking cigarettes.

The group of abstainers were broken up into two further groups: Those who stopped smoking cigarettes but used nicotine replacement products, and those who didn't consume nicotine at all. Of the women in the latter group, there were 131 regular users of e-cigarettes and 40 regular users of the Nicorette patch. Twenty-five did not use any nicotine products regularly.

Lower cotinine levels among vapers

The researchers found no significant differences between women who used only nicotine products in the final two pregnancy trimesters and those who didn't use any form of nicotine.

Abstainers using nicotine products reduced cotinine levels by 38%. Dual users, on the other hand, showed increased cotinine levels of up to 19%, while reducers' cotinine levels jumped some 10%, no matter whether they did or did not use nicotine products.

Birth weight of infants born to abstainers regularly using nicotine replacement products was higher than the birth weights of babies born to cigarette smokers. Birth weight did not differ from the weights of babies born to mothers who did not use any form of nicotine.

But Stanton Glantz, a tobacco control activist and retired professor of medicine at the University of California, San Francisco, noted that the study is limited by the fact that it doesn't mention or track the babies' health in the long-term. Glantz was not directly involved in this research.

Limitations of a study: the lack of a control group

Beyond the scope of the study over time, the University of Cincinnati's Ashley Merianos said it appeared the researchers had struggled to obtain saliva samples from many of the women — less than half ended up having their cotinine levels clinically tested. The rest of the findings were based on self-reported results.  

There was a further limitation, said Merianos, in the study's overall concept. 

Although designed as a randomized control trial — a study design considered the gold standard in clinical research, Merianos said — the paper failed, in her opinion, to include a true control group of pregnant women who did not vape or use patches.

"Rather, the study compares women who smoked cigarettes with women who vaped, and every woman involved smoked cigarettes in early pregnancy. The omission of a control group undercuts the strength of the original study design," she said.

Merianos, is currently serving as a co-investigator on two US National Institutes of Health research projects on parental tobacco cessation.

New data is better than no data

Despite these limitations, both Merianos and Glantz saw some good in the data.

"While it is encouraging that pregnant women who did not smoke in the past week but used e-cigarettes at the end of their pregnancies had reduced cotinine levels, it is alarming that there were increases in cotinine levels among those who reportedly reduced their cigarette consumption and dual-used cigarettes and e-cigarettes," said Merianos.

Glantz, meanwhile, also underlined the dangers of dual cigarette and vape use, saying that "dual use is riskier than just smoking or using e-cigs."

But in a final analysis, Merianos said the results needed to be interpreted with caution, "since the growing body of evidence points to inconclusive results about the role e-cigarettes play as a tobacco cessation aid for [an]yone, including pregnant women."

Nicotine use during pregnancy can lead to negative acute and long-term health consequences to newborns and children, including pre-term birth.