Monday July 25 2011
Giving up smoking before becoming pregnant is the ideal scenario
“Mothers using nicotine gum to avoid smoking in pregnancy ‘put unborn babies at risk’,” warned the Daily Mail. It said that the nicotine is absorbed by the foetus, which “can cause high blood pressure and heart problems later in life”.
This news is based on a study in rats that looked at how exposure to nicotine in the womb affected the large artery leading from the heart (the aorta). However, there are several reasons why a straightforward interpretation of these results to humans should be treated with caution. First, there are many differences between humans and rats. Second, it is not clear whether the levels of nicotine used in these experiments is comparable to what would be seen in women using nicotine gum or patches.
Overall, it is unsurprising that nicotine could have adverse effects on the foetus. However, the news does not seem to consider the fact that women who smoke in pregnancy will also be exposing their baby to nicotine, as well as other chemicals. Smoking is known to have adverse effects for both the mother and the child, so for women who smoke, giving up before becoming pregnant is the ideal scenario. If women who are trying to quit during pregnancy can achieve this without nicotine replacement therapies, such as patches, this would avoid any potential risk associated with nicotine.
However, if they do need nicotine replacement therapies, the long-term benefits of quitting smoking seem likely to outweigh the risks associated with continuing to smoke in pregnancy and after.
Where did the story come from?
The study was carried out by researchers from Loma Linda University School of Medicine and California State University in the US.
Funding was provided by the California Tobacco-related Disease Research Program and the National Institutes of Health. The study was published in the peer-reviewed British Journal of Pharmacology.
The Daily Mail does report that this study was in rats, but this information is only given mid-way through the story.
What kind of research was this?
This was animal research looking what effect giving nicotine to pregnant rats had on their male offspring.
The researchers report that observational studies have found that smoking in pregnancy is associated with higher blood pressure and cardiovascular disease in the adult offspring. They say that their previous experiments in rats have indicated that prenatal nicotine exposure has an effect on the blood vessels in males, making them more prone to high blood pressure. They wanted to carry out more experiments to see how nicotine had this effect.
Animal studies help us to understand the biological effects of chemical exposures, as similar experiments could not be done in humans. However, as there are obvious differences between the species, the results in rats may not fully represent what happens in humans.
What did the research involve?
The researchers took pregnant rats and implanted small pumps under their skin that continuously pumped out nicotine (in 12 rats) or a salt solution (in 13 rats) throughout the pregnancy. The researchers say that the dose of nicotine received by the rats was similar to what would be seen in the bloodstream of a moderate smoker.
When the offspring were born and reached the age of five months, the researchers compared the blood vessels in the male offspring (exposed to nicotine) with the control male offspring (exposed to salt solution). They took slices from the rats’ aortas – the large artery leading from the heart – and bathed them in a solution including a hormone called angiotensin, which makes them contract. Contraction of the blood vessels will increase blood pressure. The researchers measured how much the aorta slices contracted, and how this was affected by pre-treating the slices with different chemicals that interfere with various processes that may be affecting the contraction. One of these chemicals mimics the effect of an enzyme called SOD (superoxide dismutase), which can counteract free radicals.
The researchers also measured how much damage had been done to the aorta by free radicals in both groups of rats. Free radicals are very reactive chemicals that can damage tissue. This damage is thought to potentially play a role in cardiovascular disease.
What were the basic results?
The researchers found that the aortas from male rats exposed to nicotine in the womb contracted more strongly in response to angiotensin than control male rats not exposed to nicotine. Treating the aorta with a chemical that mimics the effect of the SOD enzyme reduced the effect of angiotensin, suggesting that the effect of angiotensin involves a pathway relating to free radicals.
They also showed that the rats exposed to nicotine in the womb had less natural activity of the SOD enzyme in their aortas, and higher levels of damage to their aortas from free radicals.
How did the researchers interpret the results?
The researchers conclude that their results show that nicotine exposure in the womb causes changes in the blood vessels that lead to an increased risk of high blood pressure in the adult offspring.
This study suggests that exposure to nicotine in the womb can lead to changes in the blood vessels of male rats.
The coverage of this study in the news implies that these results show that pregnant women who use nicotine patches are putting their unborn baby at risk of long-term cardiovascular damage. However, there are a number of reasons why direct application of these results to humans should be treated with caution:
- First, there are biological differences between different species, and this means that these results from rats may not be fully representative of what happens in humans.
- Second, the rats in this study had nicotine pumped into their bodies continuously during pregnancy. It is not clear whether the levels of nicotine that the foetuses were exposed to are similar to what would be delivered in a human by a nicotine patch. The researchers say that the levels used were similar to what would be experienced by a moderate smoker.
- Third, these rats were only assessed for relatively short-term effects on their blood vessels, and it is not certain that such effects in a human would lead to high blood pressure or increased cardiovascular events.
Overall, it is unsurprising that nicotine could have adverse effects on the foetus. However, the news does not seem to consider the fact that women who smoke in pregnancy will also be exposing their baby to nicotine, as well as other chemicals. Smoking is known to have adverse effects for both the mother and the child, and for women who smoke, giving up smoking before becoming pregnant is the best idea. If women who are trying to quit during pregnancy can achieve this without nicotine replacement therapies, such as patches, this would avoid any potential risk associated with nicotine. However, if they need nicotine replacement therapies, the long-term benefits of quitting smoking seem likely to outweigh the risks associated with continuing to smoke in pregnancy and after.
NICE guidance recommends that:
- Pregnant women who smoke are encouraged to use local evidence-based stop smoking services.
- The benefits and risks associated with nicotine replacement therapy (NRT) should be discussed with pregnant women who smoke, particularly those who do not want to accept the offer of help from the local evidence-based stop smoking services.
- NRT is used only if smoking cessation without NRT has failed.
- If a woman expresses a clear desire to use nicotine replacement therapy, doctors should use their professional judgement when deciding to offer a prescription.
- NRT is only prescribed after the woman has stopped smoking, and initially prescribed for only for two weeks, after which repeat prescriptions should be given only to women who have demonstrated that they are still not smoking.
- Pregnant women should be advised to remove nicotine patches before going to bed.