Prenatal alcohol exposure (PAE) is the most common preventable cause of developmental delay in the United States. Animal studies have shown some of the adverse effects of PAE on placental development, but few studies have examined these effects in humans.
This is the first study to examine the effects of prenatal exposure to methamphetamine, marijuana, and cigarette smoking on human placental development. Researchers collected placentas from 103 Cape Coloured (mixed ancestry) pregnant women recruited at their first antenatal clinic visit in Cape Town, South Africa. Of these, 66 heavy drinkers and 37 non-drinkers were interviewed about their alcohol, cigarette smoking, and drug use at three antenatal visits.
‘Alcohol exposure is related to decreased placental weight and a smaller placenta-to-birth weight ratio.’
A senior pathologist, blinded to exposure status, performed comprehensive pathology examinations on each placenta using a standardized protocol. In multivariable regression models, effects of prenatal exposure were examined on placental size, structure, and presence of infections and meconium.
Results show that alcohol, methamphetamine, and marijuana were associated with distinct patterns of pathology, suggesting that different mechanisms mediate their effects on placental development. Alcohol exposure was related to decreased placental weight and a smaller placenta-to-birth weight ratio. By contrast, methamphetamine was associated with larger placental weight and a larger placenta-to-birth weight ratio. Marijuana was also associated with larger placental weight.
In addition, alcohol exposure was associated with an increased risk of placental hemorrhage. Finally, alcohol and cigarette smoking were associated with a decreased risk of intrauterine passing of meconium, a sign of acute fetal stress and/or hypoxia; methamphetamine, with an increased risk. These findings may be important in the long-term teratogenic effects of prenatal alcohol and drug exposure.