Pregnancy is a dynamic state: mother and fetus undergo physiologic changes that influence drug effects. Drugs ingested by the pregnant woman reach the fetus through the maternal-placental-fetal circulation. Drugs readily cross the placenta, mainly by passive diffusion. The fetus, which is exposed to any drugs, circulating in maternal blood, is very sensitive to drug effects because it has a weak capacity for metabolizing and excreting drugs (National Institute on Drug Abuse, 1985). Once drug molecules reach the fetus, they may cause anatomic malformations or other adverse effects.
Different people react differently to the same drug. Exposure to drugs in utero, even to the same level of exposure, may have quite different effects on different infants. Additionally, we consider the dose-response relationship as effects likewise depend on the number of drugs taken by the pregnant woman, the amount, the frequency, and the timing of drug use during pregnancy. Heavier exposure to the substance is associated with worse outcomes. Physiological Damage Non-therapeutic drugs including those that are illegal are known to cause intrauterine growth retardation or IUGR and other physiologic damages.
Teratogenicity refers to anatomic malformations of an embryo or fetus (Webster's New World Medical Dicitionary, 2003) and drugs can have teratogenic effects. The National Institute for Drug Abuse has cited some drugs known to be taken by pregnant women. These drugs cause physiological and even teratogenic effects on the unborn. First on our list is cocaine. It is associated with impaired fetal growth and smaller head size at birth (Zuckerman, 1989). Newborns that were prenatally-exposed to cocaine have a lower-than-expected birth weight since cocaine, due to its ability to constrict blood vessels, decreases blood flow to the fetus.
Prenatal cocaine exposure can cause microcephaly or smaller head size in newborns. Microcephaly is thought to reflect a smaller brain. Infants with impaired fetal growth and microcephaly are more likely to experience developmental and learning problems as they get older, compared to normally grown infants with normal head size. Heavy intake of alcohol may cause poor fetal growth, altered facial features, and developmental problems or mental retardation, a phenomenon known as fetal alcohol syndrome.
Caffeine is the most commonly ingested nontherapeutic drug during pregnancy as it is present in popular drinks like coffee, tea, chocolate, etc. It causes low birth weight and cardiac dysrhythmias in the fetus. Effects of cigarette and marijuana smoking and increased fetal, neonatal, and infant mortality and decreased birth weight and length in the fetus. Overall, effects of smoking are dose related, with light smoking (less than one pack per day) estimated to increase fetal deaths by 20% and heavy smoking (one or more packs per day) increasing deaths by 35%.
Cigarette smoking has also been well documented as causing an increase in the likelihood of SIDS or Sudden Infant Death Syndrome (Zuckerman, 1986). Infants born to mother who use opiates show impaired growth and smaller head size. Damaging Effects: Neurobehavioral Studies of drug-exposed newborns suggest and array of behavioral characteristics that make their care challenging, and a few studies indicate that some prenatally-exposed infants display developmental problems as toddlers and preschoolers in areas as diverse as language, attachment to primary caregivers, ability to organize behavior, and mental and motor development.
Cocaine-exposed newborns tend to be poorly responsive and sleepy (Chasnoff, 1985). When alert, some are easily overstimulated and therefore become irritable or quickly return to sleep. The cause of some of these cocaine-exposed newborn's vacillation between sleepiness and overstimulation is unknown; it may be due to withdrawal, to a direct effect of cocaine, or to changes in the brain's neurotransmitters. Immediately after birth, some cocaine-exposed infants are often in great distress.
Jittery and suffering tremors, the infants are irritable and sensitive to the mildest environmental stimulation. Their muscles are usually stiff, and they may show a prolonged persistence or early reflexes. Often, they cry a great deal. Newborn infants of opiate-using mothers may go through withdrawal, called “neonatal abstinence syndrome,” which consists of central nervous system and digestive system symptoms that may include irritability, poor feeding, poor weight wain, ineffective sucking, yawning, sneezing and tremulousness, and sometimes seizures.
Most withdrawal symptoms disappear by age 2 months, but the irritability may persist during the first year or longer, contributing to caretaking difficulties similar to those encountered by parents of cocaine-affected infants (Kaltenbach, 1988). Chronic fetal hypoxia from heavy smoking has been associated with mental retardation and other long-term effects on physical and intellectual development. Long-term evaluation of the development of children who are exposed to cigarette smoking shows that they do less well in a variety of measure of cognitive, language, and academic achievement, including reading and mathematics (Rush, 1989).
Heavy maternal marijuana use during pregnancy was associated with poor performance of child on memory and verbal tests while children prenatally-exposed to heavy amounts of alcohol displayed poorer performance on some measures on motor development and lower scores on a test to assess their ability to maintain attention to a task. It is also linked to lower IQ scores at age 4 in other studies (Streissguth, 1989).
In their 1989 review of over 30 papers on the subject, Rush and Callahan conclude that there is a “regular and consistent pattern of lower IQ and ability, and less advanced verbal, reading, and mathematical skills associated with maternal smoking during pregnancy. ” In additional, smoking appears related to behavioral and temperamental difficulties in the children, with children of smokers appearing to have more behavioral problems, hyperactivity and inattention, and poorer social adjustment. Substance-exposed children indeed are a diverse group who are at increased vulnerability to later difficulties in learning and behavior.