Effects of antenatal drug use on the 
developing fetus


If used during pregnancy, many drugs produce teratogenic effects (e.g., skeletal and facial abnormalities) and adversely affect fetal growth and/or maturation, the developing neurologic systems, and brain organization.4,6

Drugs can also indirectly affect the fetus by interfering with the environment within the womb. Some drugs can cause contractions of the womb, decreasing the blood supply to the baby, while others may cause early, delayed, or prolonged labor.


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Infants with NAS are more likely to be born prematurely, have lower birth weight (<2,500 g), be small for gestational age, and have smaller head circumference (Table 3).4,6,7Prenatal drug exposure increases the risk for neonatal mortality, including sudden infant death syndrome, and for medical, developmental, emotional, and behavioral problems (Table 3).4,6

Table 3. Potential effects of prenatal drug exposure on birth outcomes, central nervous system development, cognitive function, and behavior

Substance Birth Effects Effects on CNS development, cognitive function, and behavior
Nicotine
  • Prematurity
  • Decreased birth height, weight, head circumference
  • Sudden infant death syndrome
  • Increased infant mortality rate
  • Excitability, hypertonia
  • Conduct disorder, reduced IQ, aggression, antisocial behavior, impulsivity, ADHD
  • Marijuana
  • No fetal growth effects
  • No physical abnormalities
  • Prematurity
  • Decreased birth height, weight, head circumference
  • Intraventricular hemorrhage
  • Cocaine
  • No fetal growth effects
  • No physical abnormalities
  • Mild withdrawal symptoms; poor autonomic control, particularly of state regulation (the ability to adjust one’s level of alertness as required for a task)
  • Executive function impairment, reading and spelling difficulty
  • Methamphetamine
  • Small for gestational age
  • Decreased birth weight
  • Poor movement quality, lower arousal, increased lethargy, increased physiological stress
  • No mental or motor delay
  • Cocaine
  • No fetal growth effects
  • No physical abnormalities
  • Mild withdrawal symptoms; poor autonomic control, particularly of state regulation (the ability to adjust one’s level of alertness as required for a task)
  • Executive function impairment, reading and spelling difficulty
  • Heroin/Opioids
  • Prematurity
  • Decreased birth height, weight, head circumference
  • Sudden infant death syndrome
  • Neonatal abstinence syndrome, less rhythmic swallowing, strabismus
  • Possible delay in general cognitive function, anxiety, aggression, disruptive/inattentive behavior
  • The outcome of the infant exposed to illicit drugs in utero depends, in part, on the quality of care the mother receives during her pregnancy.Unfortunately, stigma may prevent some pregnant women from disclosing their drug use 
and cause them to avoid or delay prenatal care.4,6

    On the other hand, pregnancy can be a motivating factor for entry into a treatment program that can improve prenatal care, optimize maternal physical and mental health, and reduce withdrawal symptoms and drug cravings.2,8

    Clinical presentation and assessment of NAS


    Many factors influence the clinical presentation of NAS, including the class of drug used during pregnancy, how much of the drug was used, time of most recent use, factors impacting maternal and fetal metabolism, neonatal immaturity or illness, and polydrug use.8Signs of withdrawal typically appear within 24 to 72 hours after birth and may last two to three days or up to eight weeks or longer.2,4,8

    The majority of NAS symptoms manifest in the central nervous system (CNS) and in the gastrointestinal (GI) tract, where opioid receptors are highly concentrated, as well as in the autonomic nervous system.2Hallmark features of NAS include extreme irritability, excessive and high-pitched crying, reduced quality and duration of sleep after a feeding, an inability to self-soothe, and increased muscle tone, tremors, and seizures.4,8Signs of autonomic dysregulation include sweating, frequent yawning and sneezing, and respiratory distress.4,8


    GI disturbances present as excessive sucking, feeding intolerance, regurgitation or vomiting, and loose or watery stools.4,8However, the presentation of GI symptoms differs according to the drug used during pregnancy.9Antenatal use of narcotics (heroin, methadone), or fentanyl (Duragesic) may cause vomiting and diarrhea.

    Feeding difficulties are associated with marijuana use, and infants exposed to cocaine may show a poor tolerance to oral feedings.9Infants exhibiting poor feeding should be evaluated for causes other than NAS, including sepsis, hypoglycemia, immaturity, bowel obstruction, and pyloric stenosis.10

    The most commonly used rating of the severity of withdrawal is a modified Finnegan Neonatal Abstinence Score, which rates the signs and symptoms of CNS disturbances; metabolic, vasomotor, and respiratory disturbances; and GI disturbances on a 5-point scale, usually at birth and every four hours or after each feeding (Figure 1).2,8,11

    Figure 1. Download the PDF.
    Figure 1

    All infants should be monitored closely for signs of fever, dehydration, or weight loss.6The duration of hospitalization depends on an accurate assessment of maternal drug history, the half-life of the drug, and response to pharmacologic treatment, if needed.2,8