an increased risk of down syndrome for infants born to those aged over 40 years. young teenaged mothers (younger than 16) and mothers over 35 are more exposed to the risks of miscarriages, premature births, and birth defects. drug use main article: drugs in pregnancy an estimated 5 percent of fetuses in the united states are exposed to illicit drug use during pregnancy. maternal drug use occurs when drugs ingested by the pregnant woman are metabolized in the placenta and then transmitted to the fetus. recent research displays that there is a correlation between fine motor skills and prenatal risk factors such as the use of psychoactive substances and signs of abortion during pregnancy. as well as perinatal risk factors such as gestation time, duration of delivery, birth weight and postnatal risk factors such as constant falls. cannabis main article: cannabis in pregnancy when using cannabis, there is a greater risk of birth defects, low birth weight, and a higher rate of death in infants or stillbirths. drug use will influence extreme irritability, crying, and risk for sids once the fetus is born. marijuana will slow the fetal growth rate and can result in premature delivery. it can also lead to low birth weight, a shortened gestational period and complications in delivery. cannabis use during pregnancy was unrelated to risk of perinatal death or need for special care, but, the babies of women who used cannabis at least once per week before and throughout pregnancy were 216g lighter than those of non‐users, had significantly shorter birth lengths and smaller head circumferences. opioids opioids including heroin will cause interrupted fetal development, stillbirths, and can lead to numerous birth defects. heroin can also result in premature delivery, creates a higher risk of miscarriages, result in facial abnormalities and head size, and create gastrointestinal abnormalities in the fetus. there is an increased risk for sids, dysfunction in the central nervous system, and neurological dysfunctions including tremors, sleep problems, and seizures. the fetus is also put at a great risk for low birth weight and respiratory problems. cocaine main article: prenatal cocaine exposure cocaine use results in a smaller brain, which results in learning disabilities for the fetus. cocaine puts the fetus at a higher risk of being stillborn or premature. cocaine use also results in low birthweight, damage to the central nervous system, and motor dysfunction. the vasoconstriction of the effects of cocaine lead to a decrease in placental blood flow to the fetus that results in fetal hypoxia (oxygen deficiency) and decreased fetal nutrition; these vasoconstrictive effects on the placenta have been linked to the number of complications in malformations that are evident in the newborn. methamphetamine prenatal methamphetamine exposure has shown to negatively impact brain development and behavioral functioning. a 2019 study further investigated neurocognitive and neurodevelopmental effects of prenatal methamphetamine exposure. this study had two groups, one containing children who were prenatally exposed to methamphetamine but no other illicit drugs and one containing children who met diagnosis criteria for adhd but were not prenatally exposed to any illicit substance. both groups of children completed intelligence measures to compute an iq. study results showed that the prenatally exposed children performed lower on the intelligence measures than their non-exposed peers with adhd. the study results also suggest that prenatal exposure to methamphetamine may negatively impact processing speed as children develop. alcohol main article: fetal alcohol spectrum disorder maternal alcohol use leads to disruptions of the fetus's brain development, interferes with the fetus's cell development and organization, and affects the maturation of the central nervous system. even small amounts of alcohol use can cause lower height, weight and head size at birth and higher aggressiveness and lower intelligence during childhood. fetal alcohol spectrum disorder is a developmental disorder that is a consequence of heavy alcohol intake by the mother during pregnancy. children with fasd have a variety of distinctive facial features, heart problems, and cognitive problems such as developmental disabilities, attention difficulties, and memory deficits. tobacco use main article: smoking and pregnancy tobacco smoking during pregnancy exposes the fetus to nicotine, tar, and carbon monoxide. nicotine results in less blood flow to the fetus because it constricts the blood vessels. carbon monoxide reduces the oxygen flow to the fetus. the reduction of blood and oxygen flow may result in miscarriage, stillbirth, low birth weight, and premature births. exposure to secondhand smoke leads to higher risks of low birth weight and childhood cancer. infections if a mother is infected with a disease, the placenta cannot always filter out the pathogens. viruses such as rubella, chicken pox, mumps, herpes, and human immunodeficiency virus (hiv) are associated with an increased risk of miscarriage, low birth weight, prematurity, physical malformations, and intellectual disabilities. hiv can lead to acquired immune deficiency syndrome (aids). untreated hiv carries a risk of between 10 and 20 per cent of being passed on to the fetus. bacterial or parasitic diseases may also be passed on to the fetus, and include chlamydia, syphilis, tuberculosis, malaria, and commonly toxoplasmosis. toxoplasmosis can be acquired through eating infected undercooked meat or contaminated food, and by drinking contaminated water. the risk of fetal infection is lowest during early pregnancy, and highest during the third trimester. however, in early pregnancy the outcome is worse, and can be fatal. maternal nutrition adequate nutrition is needed for a healthy fetus. mothers who gain less than 20 pounds during pregnancy are at increased risk for having a preterm or low birth weight infant. iron and iodine are especially important during prenatal development. mothers who are deficient in iron are at risk for having a preterm or low birth weight infant. iodine deficiencies increase the risk of miscarriage, stillbirth, and fetal brain abnormalities. adequate prenatal care gives an improved result in the newborn. low birth weight low birth weight increases an infants risk of long-term growth and cognitive and language deficits. it also results in a shortened gestational period and can lead to prenatal complications. stress stress during pregnancy can have an impact the development of the embryo. reilly (2017) states that stress can come from many forms of life events such as community, family, financial issues, and natural causes. while a woman is pregnant, stress from outside sources can take a toll on the growth in the womb that may affect the child's learning and relationships when born. for instance, they may have behavioral problems and might be antisocial. the stress that the mother experiences affects the fetus and the fetus' growth which can include the fetus' nervous system (reilly, 2017). stress can also lead to low birth weight. even after avoiding other factors like alcohol, drugs, and being healthy, stress can have its impacts whether families know it or not. many women who deal with maternal stress do not seek treatment. similar to stress, reilly stated that in recent studies, researchers have found that pregnant women who show depressive symptoms are not as attached and bonded to their child while it is in the womb (2017). environmental toxins main article: environmental toxicants and fetal development exposure to environmental toxins in pregnancy lead to higher rates of miscarriage, sterility, and birth defects. toxins include fetal exposure to lead, mercury, and ethanol or hazardous environments. prenatal exposure to mercury may lead to physical deformation, difficulty in chewing and swallowing, and poor motoric coordination. exposure to high levels of lead prenatally is related to prematurity, low birth weight, brain damage, and a variety of physical defects. exposure to persistent air pollution from traffic and smog may lead to reduced infant head size, low birth weight, increased infant death rates, impaired lung and immune system development.