use leads to increased risk for perinatal outcomes: preterm delivery, low birth weight (less than 2500 grams) or reduced birth rate, small size and earlier gestational age at delivery. prenatal cocaine exposure (pce) is associated with premature birth, birth defects, attention deficit hyperactivity disorder (adhd), and other conditions. methamphetamine use of methamphetamine is dangerous for pregnant women and to the unborn baby. methamphetamines are a class of drugs that provide stimulant-like effects, including euphoria and alertness. the drug crosses the placenta and affects the fetus during the gestational stage of pregnancy. methamphetamine use in pregnancy may lead to babies born with an earlier gestational age at delivery (pre-term), lower birth weight, and smaller head circumference. methamphetamine use during pregnancy also negatively impacts brain development and behavioral functioning and increases the risk of the baby having adhd and lower mental processing speed. opioids opioids such as heroin, fentanyl, oxycodone and methadone should not be taken while pregnant. opioid use during pregnancy may cause adverse outcomes for the women and unborn child. women who use opioids during pregnancy in a non-medical fashion are at a higher risk for premature birth, lower birth weight, still birth, specific birth defects, and withdrawal (neonatal abstinence syndrome). opioids can cross the placenta and the blood brain barrier to the fetus. opioid use is the main cause of neonatal abstinence syndrome, which is where the baby experiences withdrawals from the opioid they were exposed to during the pregnancy. typical symptoms may include tremors, convulsions, twitching, excessive crying, poor feeding or sucking, slow weight gain, breathing problems, fever, diarrhea, and vomiting. there is no consensus on the effects on cognitive abilities. further research is required to determine the long-term effects of in utero exposure to opioid medications on children. tobacco main article: smoking and pregnancy smoking during pregnancy is dangerous to the unborn baby and may cause pre-term birth, birth defects such as cleft lip or cleft palate, or miscarriage. tobacco is the most commonly used substance among pregnant women, at 25%. nicotine crosses the placenta and accumulates within fetal tissues. children born to women who smoked heavily were more susceptible to behavioral problems such as adhd, poor impulse control, and aggressive behaviors. tobacco contains carbon monoxide, which has the potential to prevent the fetus from receiving sufficient oxygen. other health concerns tobacco poses are premature birth, low birth weight, and an increased risk of sudden infant death syndrome (sids) of up to three times compared to infants not exposed to tobacco. smoking and pregnancy, combined, cause twice the risk of premature rupture of membranes, placental abruption and placenta previa. in addition to the fetus, women in general who smoke heavily are less likely to become pregnant. pregnancy categories main article: pregnancy category until 2014, the u.s. code of federal regulations required that certain drugs and biological products be labelled specifically with respect to their effects on pregnant populations, including a definition of a "pregnancy category". these rules were enforced by the fda, and medications that have been studied for their effects in pregnancy fell under the following pregnancy categories: a, b, c, d, or x depending on how they have been studied and what kind of results were found from the studies. in 2014, however, the fda has developed a "pregnancy and lactation labeling rule (pllr)" which requires product labels to include specific information related to the safety and effectiveness of medications to pregnant and lactating women. this ruling has removed the requirement of stating pregnancy categories in prescription drug labels. australia's categorization system takes into account birth defects, the effects around birth or when the mother gives birth, and problems that will arise later in the child's life due to the drug taken. the system places them into a category based on the severity of the consequences that the drug can have on the infant when it crosses the placenta.