Drugs taken by pregnant women during pregnancy can affect the fetus in the following ways: by direct action on the fetus, causing damage, abnormal development or death. By altering the function of the placenta, often by causing constriction of the placental blood vessels, reducing the exchange of oxygen and nutrients between the mother and the fetus. By causing powerful contractions of the uterine muscles, reducing the blood supply to the fetus and damaging the fetus. The effect of a drug on the fetus depends on the stage of development of the fetus at the time of administration, as well as the potency and dose of the drug. Some drugs taken early in pregnancy, before 17 days after fertilization, can have an “all-or-nothing” effect on the fetus; they can either kill the embryo or have no effect at all. During this period, the fetus has a high tolerance to teratogenic drugs. However, between 17 and 57 days after fertilization, the fetus is particularly sensitive to the effects of teratogenic factors. Because this is the period of organ development, drugs entering the fetus at this time can cause miscarriage, obvious congenital malformations, or cause some permanent defects that are not easily detected at birth and are later discovered, or have insignificant effects. After organ development is complete, drugs are unlikely to cause significant congenital malformations, but can affect later fetal growth and development and the formation of normal organ and tissue function. Anticancer drugs Many anticancer drugs can cause congenital malformations, such as intrauterine growth retardation, jaw hypoplasia, cleft palate, abnormal cranial development, neural tube defects, deformed feet, and mental retardation. Reactive arrest This drug is no longer given to pregnant women because it can cause significant congenital malformations in the fetus, including severe incomplete development of the upper and lower extremities, as well as malformations of the intestines, heart, and blood vessels. Dermatological agents Isotretinoin is used to treat severe acne, psoriasis and other skin conditions. It can cause severe congenital malformations, most notably cardiac malformations, microtia and hydrocephalus. The teratogenic risk rate is approximately 25%. Etretinate, another drug used to treat skin conditions, can also cause congenital malformations in humans. Therefore, women who use this drug should not become pregnant until at least one year after stopping it. Sex hormones Androgens are used to treat various blood disorders. If androgens and synthetic progestins are used in the first 12 weeks after fertilization. It can masculinize the external genitalia of a female fetus. Hexestrol is a synthetic estrogen. Pregnant women who have taken hexestrol during pregnancy give birth to baby girls who may develop adenocarcinoma of the vagina during adolescence. Also, such girls are at increased risk of subsequent uterine cavity abnormalities, menstrual disorders, cervical insufficiency, spontaneous abortion, ectopic pregnancy, and fetal death before birth. Affected male fetuses can develop penile malformations. Meclozine Meclozine is often used for nausea and vomiting due to motion sickness and can cause congenital malformations in animals, but no similar malformations have been found in humans. Antiepileptic drugs Women with epilepsy who have taken certain antiepileptic drugs during pregnancy may have fetuses with cleft palates and abnormal development of the heart, face, bones, hands, and internal organs. Mental retardation may also occur. Two antiepileptic drugs are particularly likely to cause congenital malformations: trimethoprim has a teratogenic risk rate of about 70%; valproic acid has a risk rate of about 1%. Carbamazepine, another antiepileptic, is thought to cause a considerable number of unimportant birth defects. Babies born to pregnant women who have used phenytoin sodium and phenobarbital are prone to bleeding at birth. This is because these drugs can cause vitamin K deficiency. Vaccines Vaccines made from live viruses should not be used in women who are going to be pregnant or who are already pregnant, except in special cases. They should only be given if they are at real risk of contracting these microorganisms. Thyroid medications If necessary, propylthiouracil is usually used because it is well tolerated by both the fetus and the pregnant woman. Oral hypoglycemic agents Insulin is available to control diabetes in pregnant women. Narcotics and non-steroidal anti-inflammatory drugs Aspirin or other non-steroidal anti-inflammatory drugs can delay labor episodes if taken in large amounts during pregnancy. Can cause the ductus arteriosus, the connection between the aorta and pulmonary artery of the fetus, to close before birth. Non-steroidal anti-inflammatory drugs used late in pregnancy can reduce the amount of amniotic fluid, a potential risk to the fetus. Taking high doses of aspirin can cause bleeding in the pregnant woman and the newborn. Aspirin or other salicylates can cause increased bilirubin levels in the fetal blood, producing jaundice and occasionally damaging the fetal brain. Anti-anxiety and antidepressant drugs Taking anti-anxiety drugs in the first trimester has the potential to cause congenital malformations in the fetus. Most antidepressants are relatively safe when applied during pregnancy. However, lithium can cause congenital malformations, mainly heart malformations Antibiotics Tetracycline can be deposited in fetal bones and teeth through the placenta to bind with calcium, and should be avoided during pregnancy. Antibiotics such as streptomycin and kanamycin used during pregnancy can damage the inner ear of the fetus and cause deafness. Chloramphenicol is not harmful to the fetus but can cause gray baby syndrome in newborns. Ciprofloxacin should not be used during pregnancy because it has been shown to cause joint deformities in animals. Penicillin is safe. Most sulfonamide antibiotics can also cause jaundice in newborns when taken late in pregnancy and can cause brain damage in severe cases, but one sulfonamide antibiotic, salazosulfapyridine, rarely causes this side effect. Anticoagulants The developing fetus is highly sensitive to warfarin. If this drug is taken within the first trimester of pregnancy, significant congenital malformations may occur in about 1 in 4 infants. Also, abnormal bleeding may occur in both the fetus and the mother. Anticoagulation with heparin is relatively much safer. However, continued use can also lead to reduced platelet counts or osteoporosis in pregnant women. Medications for cardiovascular disease Frequent medication to lower blood pressure in pregnant women with pre-eclampsia or eclampsia can affect placental function. Drugs such as furantoin, vitamin K, sulfonamide and chloramphenicol during pregnancy can cause fetal and maternal hemolysis in glucose-6 phosphate dehydrogenase (G6PD) deficient women. Drugs used during labor and delivery Local anesthetics, narcotics and other analgesics can generally affect the newborn through the placenta, causing respiratory distress to occur. Therefore, if anesthetics are required during labor and delivery, the smallest effective dose should be given and administration should be delayed as much as possible so that the fetus absorbs as little anesthetic as possible before delivery. Other drugs Smoking, smoking during pregnancy is harmful. The average birth weight of babies born to mothers who smoked during pregnancy is 170 g less than babies born to nonsmoking mothers, and the incidence of miscarriage, stillbirth, and sudden infant death syndrome (SIDS) may be increased in babies born to mothers who smoked during pregnancy. Alcohol consumption, when consumed by pregnant women during pregnancy, can cause neonatal defects. Fetal alcohol syndrome may occur in pregnant women who consume large amounts of alcohol. These infants have growth retardation, small heads, facial deformities, and mental retardation. Less common defects are joint deformities and heart malformations. It is not known whether excessive coffee consumption during pregnancy is harmful to the newborn. Cocaine, used during pregnancy, can increase the risk of miscarriage, early placental abruption, congenital malformations of the brain, kidneys, and reproductive organs. It is relatively uncommon to cause behavioral abnormalities in newborns.