Cigarette smoking during pregnancy has been associated with an increased risk of various problems for the fetus and the mother. The risk is dose-dependent, so that the more a woman smokes during pregnancy, the higher the risk for adverse effects. Luckily, women who inadvertently smoked during the beginning of their pregnancy because they were not yet aware of the pregnancy have a good chance for a normal outcome if they cease smoking in the later months of pregnancy.
Miscarriage and Infant Death
Many studies have associated maternal cigarette smoking during pregnancy with increased rates of miscarriage and infant death. Smoking constricts blood vessels supplying the placenta, leading to decreased blood flow to the fetus. Without sufficient blood flow, the fetus is deprived of nutrients and oxygen, which can lead to growth restriction and even death. Even after birth, the death rate is increased for babies whose mothers smoked during pregnancy. The results of a National Vital Statistics Reports study from 2006 indicated that infants of smokers had a mortality rate 71 percent higher than infants of nonsmokers (11.25 percent versus 6.65 percent). Exposure to second-hand smoke after birth also increases the risk of infant death, SIDS and health problems such as asthma.
Growth Restriction and Birth Defects
Decreased blood flow in the arteries serving the placenta can lead to growth restriction in the fetus. Growth restriction can be noted prenatally by ultrasound when the fetal measurements lag behind expected measurements for each gestational age. At birth, growth restriction can result in low birth weight, small body size and small head circumference. The rate of preterm birth is also approximately doubled with maternal smoking. Preterm babies and those that are underweight face increased risks for several challenges later on, including learning disabilities, lower IQ scores, psychiatric disorders such as depression, and behavioral problems.
Smoking during pregnancy may also increase the risk for birth defects in the baby, although study results have been inconsistent regarding whether smoking can actually cause birth defects. The highest potential for birth defects is during the first trimester of pregnancy, when the fetal organs are developing. A large study published in 2000 in the journal Plastic and Reconstructive Surgery noted a significant association between smoking during pregnancy and cleft lip with or without cleft palate in the fetus. Maternal smoking may also increase the risk for heart defects and digestive system abnormalities.
Other Pregnancy Complications
In addition to adverse effects for the fetus, smoking can also cause several pregnancy complications. First, women who smoke experience lowered fertility, so it generally takes them longer to achieve a pregnancy. Smokers who get pregnant have approximately double the risk for developing problems with the placenta, such as placenta previa (when the placenta lies on top of the cervix) and placental abruption (when the placenta prematurely separates from the uterine wall). These complications can cause excessive bleeding during delivery, which jeopardizes the health of the mother and infant. Smoking also increases the risk for premature rupture of the membranes, which can lead to preterm delivery.
References
- "National Vital Statistics Reports"; Infant Mortality Statistics from the 2003 Period Linked Birth/Infant Death Data Set; Mathews et al; 2006
- "Plastic and Reconstructive Surgery"; Maternal Cigarette Smoking During Pregnancy and the Risk of Having a Child With Cleft Lip/Palate; KC Chung et al; Feb. 2000
