Smoking and pregnancy

Pregnant woman smoking outside a London hospital

Tobacco smoking and pregnancy is related to many effects on health and reproduction, in addition to the general health effects of tobacco. A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the fetus.^[1][2]

Ideally, women should not smoke before, during or after pregnancy. If this is not the case, however, the daily number of cigarettes can be reduced to minimize the risks for both the mother and child. This is particularly important for women in developing countries where breastfeeding is essential for the child's overall nutritional status.^[3]

Smoking before pregnancy

It is recommended for women planning pregnancy to stop smoking.^[4] It is important to examine these effects because smoking before, during and after pregnancy is not an unusual behavior among the general population and can have detrimental health impacts, especially among both mother and child as a result. In 2011, approximately 10% of pregnant women in data collected from 24 states reported smoking during the last three months of their pregnancy.^[5]

Smoking during pregnancy

According to a study conducted in 2008 by the Pregnancy Risk Assessment Monitoring System (PRAMS) that interviewed women in 26 states in the United States, approximately 13% of women reported smoking during the last 3 months of pregnancy. Of women who smoked during the last 3 months of pregnancy, 52% reported smoking 5 or fewer cigarettes per day, 27% reported smoking 6 to 10 cigarettes per day, and 21% reported smoking 11 or more cigarettes per day.^[6]

In the United States, women whose pregnancies were unintended are 30% more likely to smoke during pregnancy than those whose pregnancies were intended.^[7]

Effects on ongoing pregnancy

Smoking during pregnancy can lead to a plethora of health risks to both the mother and the fetus.

Women who smoke during pregnancy are about twice as likely to experience the following pregnancy complications:^[8]

• premature rupture of membranes, which means that the amniotic sac will rupture prematurely, and will induce labour before the baby is fully developed. Although this complication has a good prognosis (in Western countries), it causes stress as the premature child may have to stay in the hospital to gain health and strength to be able to sustain life on their own.
• placental abruption, wherein there is premature separation of the placenta from the attachment site. The fetus can be put in distress, and can even die. The mother can lose blood and can have a haemorrhage; she may need a blood transfusion.
• placenta previa, where in the placenta grows in the lowest part of the uterus and covers all or part of the opening to the cervix.^[9] Having placenta previa is an economic stress as well because it requires having a caesarean section delivery, which require a longer recovery period in the hospital. There can also be complications, such as maternal hemorrhage.

Premature birth

Some studies show that the probability of premature birth is roughly 1% higher for women who smoke during pregnancy going from around -1% to 1%.^[10]

Implications for the umbilical cord

Smoking can also impair the general development of the placenta, which is problematic because it reduces blood flow to the foetus. When the placenta does not develop fully, the umbilical cord which transfers oxygen and nutrients from the mother's blood to the placenta, cannot transfer enough oxygen and nutrients to the foetus, which will not be able to fully grow and develop. These conditions can result in heavy bleeding during delivery that can endanger mother and baby, although cesarean delivery can prevent most deaths.^[11]

Pregnancy-induced hypertension

There is limited evidence that smoking reduces the incidence of pregnancy-induced hypertension,^[12] but not when the pregnancy is with more than one baby (i.e. it has no effect on twins etc.).^[13]

Effects of smoking during pregnancy on the child after birth

Low birth weight

Smoking during pregnancy can result in lower birth weight as well as deformities in the baby.^[14] Smoking nearly doubles the risk of low birthweight babies. In 2004, 11.9% of babies born to smokers had low birthweight as compared to only 7.2% of babies born to nonsmokers. More specifically, infants born to smokers weigh on average 200 grams less than infants born to women who do not smoke.^[15]

The nicotine in cigarette smoke constricts the blood vessels in placenta and carbon monoxide, which is poisonous, enters the baby's bloodstream, replacing some of the valuable oxygen molecules carried by hemoglobin in the red blood cells. Moreover, because the fetus cannot breathe the smoke out, he has to wait for the placenta to clear it. These effects account for the fact that, on average, babies born to smoking mothers are usually born too early and have low birth weight (less than 2,500 grams or 5.5 pounds), making it more likely the baby will become sick or die. ^[16]

Premature and low birth weight babies face an increased risk of serious health problems as newborns have chronic lifelong disabilities such as cerebral palsy (a set of motor conditions causing physical disabilities), mental retardation and learning problems.

Sudden infant death syndrome

Sudden infant death syndrome (SIDS) is the sudden death of an infant that is unexplainable by the infant's history. The death also remains unexplainable upon autopsy. Infants exposed to smoke, both during pregnancy and after birth, are found to be more at risk of SIDS due to the increased levels of nicotine often found in SIDS cases. Infants exposed to smoke during pregnancy are up to three times more likely to die of SIDS that children born to non-smoking mothers. ^[17]

Other birth defects

Smoking can also cause other birth defects, reduced birth circumference, altered brainstem development, altered lung structure, and cerebral palsy. Recently the U.S. Public Health Service reported that if all pregnant women in the United States stopped smoking, there would be an estimated 11% reduction in stillbirths and a 5% reduction in newborn deaths.^[15]

Future obesity

A recent study has proposed that maternal smoking during pregnancy can lead to future teenage obesity. While no significant differences could be found between young teenagers with smoking mothers as compared to young teenagers with nonsmoking mothers, older teenagers with smoking mothers were found to have on average 26 percent more body fat and 33 percent more abdominal fat than similar aged teenagers with non-smoking mothers. This increase in body fat may result from the effect smoking during pregnancy, which is thought to impact fetal genetic programming in relation to obesity. While the exact mechanism for this difference is currently unknown, studies conducted on animals have indicated that nicotine may affect brain functions that deal with eating impulses and energy metabolism. These differences appear to have a significant effect on the maintenance of a healthy, normal weight. As a result of this alteration to brain functions, teenage obesity can in turn lead to a variety of health problems including diabetes (a condition in which the affected individual's blood glucose level is too high and the body is unable to regulate it), hypertension (high blood pressure), and cardiovascular disease (any affliction related to the heart but most commonly the thickening of arteries due to excess fat build-up).^[19]

Future smoking habits

Studies indicate that smoking during pregnancy increases the likelihood of offspring beginning to smoke at an early age.

Quitting during pregnancy

Quitting smoking at any point during pregnancy is more beneficial than continuing to smoke throughout the entire 9 months of pregnancy, especially if it is done within the first trimester (within the first 12 weeks of pregnancy). A recent study suggests, however, that women who smoke anytime during the first trimester put their fetus at a higher risk for birth defects, particularly congenital heart defects (structural defects in the heart of an infant that can hinder blood flow) than women who have never smoked. That risk only continues to increase the longer into the pregnancy a woman smokes, as well as the larger number of cigarettes she is smoking. This continued increase in risk throughout pregnancy means that it can still be beneficial for a pregnant woman to quit smoking for the remainder of her gestation period.^[11]

There are many resources to help pregnant women quit smoking such as counseling and drug therapies. For non-pregnant smokers, an often-recommended aid to quitting smoking is through the use of Nicotine replacement therapy in the form of patches, gum, inhalers, lozenges, sprays or sublingual tablets (tablets which you place under the tongue). However, it is important to note that the use of Nicotine Replacement Therapies (NRTs) is questionable for pregnant women as these treatments still deliver nicotine to the child. For some pregnant smokers, NRT might still be the most beneficial and helpful solution to quit smoking. It is important to talk to your doctor to determine the best course of action on an individual basis.^[20]

Smoking after pregnancy

Infants exposed to smoke, both during pregnancy and after birth, are found to be more at risk of sudden infant death syndrome (SIDS).^[17]

Breastfeeding

If one does continue to smoke after giving birth, however, it is still more beneficial to breastfeed than to completely avoid this practice altogether. There is evidence that breastfeeding offers protection against many infectious diseases, especially diarrhea. Even in babies exposed to the harmful effects of nicotine through breast milk, the likelihood of acute respiratory illness is significantly diminished when compared to infants whose mothers smoked but were formula fed.^[21] Regardless, the benefits of breastfeeding outweigh the risks of nicotine exposure.

Passive smoking

Passive smoking is associated with many risks to children, including, sudden infant death syndrome (SIDS),^[22][23] asthma,^[24][25] lung infections,^{[26][27][28][29]} impaired respiratory function and slowed lung growth,^[8] Crohn's disease,^[30] learning difficulties and neurobehavioral effects,^[31][32] an increase in tooth decay,^[33] and an increased risk of middle ear infections.^[34][35]

Multigenerational effect

A grandmother who smoked during the pregnancy of her daughter transmits an increased risk of asthma to her grandchildren, even if the second-generation mother did not smoke.^[36] The multigenerational epigenetic effect of nicotine on lung function has already been demonstrated.^[36]

See also

• Health effects of tobacco

References

External links

• CDC - Tobacco Use and Pregnancy - Reproductive Health