showed elevated risks for other tumors and congenital malformations of the sex organs for both sexes. all cytostatics are strong teratogens; abortion is usually recommended when pregnancy is discovered during or before chemotherapy. aminopterin, a cytostatic drug with antifolate effect, was used during the 1950s and 1960s to induce therapeutic abortions. in some cases, the abortion did not happen, but the newborns had a fetal aminopterin syndrome consisting of growth retardation, craniosynostosis, hydrocephalus, facial dismorphities, intellectual disability, or leg deformities toxic substances drinking water is often a medium through which harmful toxins travel. heavy metals, elements, nitrates, nitrites, and fluoride can be carried through water and cause congenital disorders. nitrate, which is found mostly in drinking water from ground sources, is a powerful teratogen. a case-control study in rural australia that was conducted following frequent reports of prenatal mortality and congenital malformations found that those who drank the nitrate-containing groundwater, as opposed to rain water, ran the risk of giving birth to children with central nervous system disorders, muscoskeletal defects, and cardiac defects. chlorinated and aromatic solvents such as benzene and trichloroethylene sometimes enter the water supply due to oversights in waste disposal. a case-control study on the area found that by 1986, leukemia was occurring in the children of woburn, massachusetts, at a rate that was four times the expected rate of incidence. further investigation revealed a connection between the high occurrence of leukemia and an error in water distribution that delivered water to the town with significant contamination with manufacturing waste containing trichloroethylene. as an endocrine disruptor, ddt was shown to induce miscarriages, interfere with the development of the female reproductive system, cause the congenital hypothyroidism, and suspectably childhood obesity. fluoride, when transmitted through water at high levels, can also act as a teratogen. two reports on fluoride exposure from china, which were controlled to account for the education level of parents, found that children born to parents who were exposed to 4.12 ppm fluoride grew to have iqs that were, on average, seven points lower than their counterparts whose parents consumed water that contained 0.91 ppm fluoride. in studies conducted on rats, higher fluoride in drinking water led to increased acetylcholinesterase levels, which can alter prenatal brain development. the most significant effects were noted at a level of 5 ppm. the fetus is even more susceptible to damage from carbon monoxide intake, which can be harmful when inhaled during pregnancy, usually through first- or second-hand tobacco smoke. the concentration of carbon monoxide in the infant born to a nonsmoking mother is around 2%, and this concentration drastically increases to a range of 6%–9% if the mother smoked tobacco. other possible sources of prenatal carbon monoxide intoxication are exhaust gas from combustion motors, use of dichloromethane (paint thinner, varnish removers) in enclosed areas, defective gas water heaters, indoor barbeques, open flames in poorly ventilated areas, and atmospheric exposure in highly polluted areas. exposure to carbon monoxide at toxic levels during the first two trimesters of pregnancy can lead to intrauterine growth restriction, leading to a baby who has stunted growth and is born smaller than 90% of other babies at the same gestational age. the effect of chronic exposure to carbon monoxide can depend on the stage of pregnancy in which the mother is exposed. exposure during the embryonic stage can have neurological consequences, such as telencephalic dysgenesis, behavioral difficulties during infancy, and reduction of cerebellum volume. also, possible skeletal defects could result from exposure to carbon monoxide during the embryonic stage, such as hand and foot malformations, hip dysplasia, hip subluxation, agenesis of a limb, and inferior maxillary atresia with glossoptosis. also, carbon monoxide exposure between days 35 and 40 of embryonic development can lead to an increased risk of the child developing a cleft palate. exposure to carbon monoxide or polluted ozone exposure can also lead to cardiac defects of the ventrical septal, pulmonary artery, and heart valves. the effects of carbon monoxide exposure are decreased later in fetal development during the fetal stage, but they may still lead to anoxic encephalopathy. industrial pollution can also lead to congenital defects. over a period of 37 years, the chisso corporation, a petrochemical and plastics company, contaminated the waters of minamata bay with an estimated 27 tons of methylmercury, contaminating the local water supply. this led many people in the area to develop what became known as the "minamata disease". because methylmercury is a teratogen, the mercury poisoning of those residing by the bay resulted in neurological defects in the offspring. infants exposed to mercury poisoning in utero showed predispositions to cerebral palsy, ataxia, inhibited psychomotor development, and intellectual disability. landfill sites have been shown to have adverse effects on fetal development. extensive research has shown that landfills have several negative effects on babies born to mothers living near landfill sites: low birth weight, birth defects, spontaneous abortion, and fetal and infant mortality. studies done around the love canal site near niagara falls and the lipari landfill in new jersey have shown a higher proportion of low birth-weight babies than communities farther away from landfills. a study done in california showed a positive correlation between time and quantity of dumping and low birth weights and neonatal deaths. a study in the united kingdom showed a correlation between pregnant women living near landfill sites and an increased risk of congenital disorders, such as neural tube defects, hypospadias, epispadia, and abdominal wall defects, such as gastroschisis and exomphalos. a study conducted on a welsh community also showed an increased incidence of gastroschisis. another study on 21 european hazardous-waste sites showed that those living within 3 km had an increased risk of giving birth to infants with birth defects and that as distance from the land increased, the risk decreased. these birth defects included neural tube defects, malformations of the cardiac septa, anomalies of arteries and veins, and chromosomal anomalies. looking at communities that live near landfill sites brings up environmental justice. a vast majority of sites are located near poor, mostly black, communities. for example, between the early 1920s and 1978, about 25% of houston's population was black. however, over 80% of landfills and incinerators during this time were located in these black communities. another issue regarding environmental justice is lead poisoning. a fetus exposed to lead during the pregnancy can result in learning difficulties and slowed growth. some paints (before 1978) and pipes contain lead. therefore, pregnant women who live in homes with lead paint inhale the dust containing lead, leading to lead exposure in the fetus. when lead pipes are used for drinking water and cooking water, this water is ingested, along with the lead, exposing the fetus to this toxin. this issue is more prevalent in poorer communities because more well-off families are able to afford to have their homes repainted and pipes renovated. smoking paternal smoking prior to conception has been linked with the increased risk of congenital abnormalities in offspring. smoking causes dna mutations in the germline of the father, which can be inherited by the offspring. cigarette smoke acts as a chemical mutagen on germ cell dna. the germ cells suffer oxidative damage, and the effects can be seen in altered mrna production, infertility issues, and side effects in the embryonic and fetal stages of development. this oxidative damage may result in epigenetic or genetic modifications of the father's germline. fetal lymphocytes have been damaged as a result of a father's smoking habits prior to conception. correlations between paternal smoking and the increased risk of offspring developing childhood cancers (including acute leukemia, brain tumors, and lymphoma) before age five have been established. little is currently known about how paternal smoking damages the fetus, and what window of time in which the father smokes is most harmful to offspring. infections main article: vertically transmitted infection a vertically transmitted infection is an infection caused by bacteria, viruses, or in rare cases, parasites transmitted directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth. congenital disorders were initially believed to be the result of only hereditary factors. however, in the early 1940s, australian pediatric ophthalmologist norman gregg began recognizing a pattern in which the infants arriving at his surgery were developing congenital cataracts at a higher rate than those who developed it from hereditary factors. on october 15, 1941, gregg delivered a paper that explained his findings-68 out of the 78 children with congenital cataracts had been exposed in utero to rubella due to an outbreak in australian army camps. these findings confirmed, to gregg, that, in fact, environmental causes for congenital disorders could exist. rubella is known to cause abnormalities of the eye, internal ear, heart, and sometimes the teeth. more specifically, fetal exposure to rubella during weeks five to ten of development (the sixth week particularly) can cause cataracts and microphthalmia in the eyes. if the mother is infected with rubella during the ninth week, a crucial week for internal ear development, destruction of the organ of corti can occur, causing deafness. in the heart, the ductus arteriosus can remain after birth, leading to hypertension. rubella can also lead to atrial and ventricular septal defects in the heart. if exposed to rubella in the second trimester, the fetus can develop central nervous system malformations. however, because infections of rubella may remain undetected, misdiagnosed, or unrecognized in the mother, and/or some abnormalities are not evident until later in the child's life, precise incidence of birth defects due to rubella are not entirely known. the timing of the mother's infection during fetal development determines the risk and type of birth defect. as the embryo develops, the risk of abnormalities decreases. if exposed to the rubella virus during the first four weeks, the risk of malformations is 47%. exposure during weeks five through eight creates a 22% chance, while weeks 9–12, a 7% chance exists, followed by 6% if the exposure is during the 13th-16th weeks. exposure during the first eight weeks of development can also lead to premature birth and fetal death. these numbers are calculated from immediate inspection of the infant after birth. therefore, mental defects are not accounted for in the percentages because they are not evident until later in the child's life. if they were to be included, these numbers would be much higher. other infectious agents include cytomegalovirus, the herpes simplex virus, hyperthermia, toxoplasmosis, and syphilis. maternal exposure to cytomegalovirus can cause microcephaly, cerebral calcifications, blindness, chorioretinitis (which can cause blindness), hepatosplenomegaly, and meningoencephalitis in fetuses. microcephaly is a disorder in which the fetus has an atypically small head, cerebral calcifications means certain areas of the brain have atypical calcium deposits, and meningoencephalitis is the enlargement of the brain. all three disorders cause abnormal brain function or intellectual disability. hepatosplenomegaly is the enlargement of the liver and spleen which causes digestive problems. it can also cause some kernicterus and petechiae. kernicterus causes yellow pigmentation of the skin, brain damage, and deafness. petechaie is when the capillaries bleed resulting in red/purple spots on the skin. however, cytomegalovirus is often fatal in the embryo. the zika virus can also be transmitted from the pregnant mother to her baby and cause microcephaly. the herpes simplex virus can cause microcephaly, microphthalmus (abnormally small eyeballs), retinal dysplasia, hepatosplenomegaly, and intellectual disability. both microphthalmus and retinal dysplasia can cause blindness. however, the most common symptom in infants is an inflammatory response that develops during the first three weeks of life. hyperthermia causes anencephaly, which is when part of the brain and skull are absent in the infant. mother exposure to toxoplasmosis can cause cerebral calcification, hydrocephalus (causes mental disabilities), and intellectual disability in infants. other birth abnormalities have been reported as well, such as chorioretinitis, microphthalmus, and ocular defects. syphilis causes congenital deafness, intellectual disability, and diffuse fibrosis in organs, such as the liver and lungs, if the embryo is exposed. malnutrition further information: nutrition in pregnancy and folate deficiency for example, a lack of folic acid, a b vitamin, in the diet of a mother can cause cellular neural tube deformities that result in spina bifida. congenital disorders such as a neural tube deformity can be prevented by 72% if the mother consumes 4 mg of folic acid before the conception and after twelve weeks of pregnancy. folic acid, or vitamin b9,