The Maternal and Fetal Physiologic Effects of Nicotine.
By D.S Lambers and K.E. Clark. (1996). Seminars in Perinatology 20 (2), 115-126.
This comprehensive and informative review of the physiologic effects of nicotine on mothers and fetuses cites key studies and statistics revealing both the pervasive, injurious effects of smoking, and incentives for breaking the habit. More than 22 million American women are smoking, the vast majority (87%) of whom began before 18 years of age. In fact, about 90% of new female smokers are teens. Only 2.5 % of smokers succeed in escaping from nicotine addiction. Fifteen percent continue to smoke throughout pregnancy. Of these, only 18% are able to quit during pregnancy, although doing so could result in measurable improvements in both weight (an additional 241 g.) and an additional week of gestation in the womb.
Table 1 conveniently lists the known adverse reproductive consequences of smoking: premature birth, intrauterine growth restriction, premature rupture of membranes, preterm labor, placental abruption, spontaneous abortion, and placenta previa.
Table 2 lists the complications for the baby of the smoker: low-birthweight, Sudden Infant Death Syndrome, asthma, lower IQ (5 points lower), smaller head circumference, behavior problems, attention deficit disorder, and upper respiratory infections.
Nicotine, the chief alkaloid in tobacco, directly stimulates acetylcholine receptors primarily located in the autonomic ganglion, adrenal medulla, and neuromuscular junctions releasing a multitude of vasoactive catecholamines and peptides. It is metabolized in the liver where over 20 metabolites have been identified. The primary one is cotinine which has a half life of 15-20 hours and concentrates in serum 10-fold higher than nicotine itself which means that the prenate gets larger doses than the mother, 54% larger dose according to one study, and an 88% higher dose according to another.
The effects of nicotine are seen in every trimester from spontaneous abortions in first trimester to premature delivery and decreased birthweight in the third. Smoking poses a 33% risk of fetal death after 20 weeks g.a. as well as death in the first 28 days of life. Smoking reduces fertility, a problem which can be reversed after breaking the addiction. Average weight of babies exposed to nicotine in utero is from 100 to 320 g. lighter than babies born to non-smoking mothers. Nicotine decreases uterine blood flow by 30 to 40% depending on the dose. And 78% of women are smoking brands yielding high amounts of nicotine which reduce nutrients and oxygen supply to fetal tissues. Smoking results in respiratory problems in the baby because nicotine interferes with normal construction of microvilli and other basic structures of the lungs. Nicotine interferes with formation of elastic tissue leading to emphysema-like rigidity of the neonatal lungs.
Mental and behavioral problems from nicotine exposure include attention deficit disorder, lower scores in expressive language and conceptual comprehension, smaller heads and lower height, and compromised arterial blood flow in the brain. Passive smoke exposure significantly adds to the effects of the mother,s smoking alone.
One ray of hope: The number of mothers smoking during pregnancy has decreased from 48% in the 1950,s to 16% currently.
Smoking and the Sudden Infant Death Syndrome: Results from 1993-1995 Case-Controlled Study for Confidential Inquiry into Stillbirths and Deaths in Infancy.
By P.S. Blair, P.J. Fleming, D. Bensley, I. Smith, C. Bacon, E. Taylor, J.G. Berry and J. Tripp. (1996). British Medical Journal 313 (27 July), 195-198.
This study was done in England, beginning a year after a national "Back to Sleep campaign in 1991 had caused the incidence of S.I.D.S to fall. Yet, this malady was still responsible for the largest single group of deaths of infants in the first year of life. Parental interviews were conducted for each infant who died and four controls were matched for age and date of interview. The one hundred ninety five babies who died and the 780 controls were drawn from three regions in England with a total population of 17 million people, giving the study extraordinary authority.
Compared to controls, the dead babies had mothers who smoked during pregnancy, 63% to 25%. Paternal smoking had an additional independent effect. The more the mother smoked, the greater the risk of death to the infant. The risk of death rose with increasing postnatal exposure to tobacco smoke after prenatal exposure. The authors of the study concluded that about 60% of S.I.D.S deaths are due to the effects of exposure to tobacco smoke before and after birth. They estimate that these deaths could be reduced by almost two thirds if parents did not smoke.
Placental Transfer of Selected Substances of Abuse.
B.B. Little and T.T. Beveren (1996). Seminars in Perinatology 20 (2), 147-153.
One of the early myths in the field of obstetrics, lasting into the late 1950,s, was that the placenta functioned as a barrier organ to protect the fetus from multiple noxious elements which might be circulating in the mother,s system. Although thoroughly discredited by modern research revealing that the placenta is an organ of transfer rather than a barrier, this myth gives the appearance of being alive and well in the minds of many mothers today. Substance abuse during pregnancy in the United States is at epidemic levels, with some hospitals reporting that more than 50% of pregnant women were using a substance of abuse in the peri-partum period, although wider studies estimate the national average closer to 15%. Substance abuse in pregnancy is therefore a national public health problem.
The bad news: Virtually all substances of abuse freely cross the placenta exposing the fetus to whatever the mother may be using. This review gets specific about the placental transfer of the 17 leading substances of abuse (Table 3). The technicalities of placental transfer are summarized in Table 1.