A major challenge of use of medications in pregnancy is that the vast majority of drugs have not been tested extensively on pregnant women. The obvious difficulty with using any type of medication in pregnancy is that the pregnancy drug categories are so broad based and the definitions are so varied within each category. If one uses the pregnancy categories only, it is difficult for the average physician to confidently prescribe medications safely in pregnancy. The majority of drugs are listed as pregnancy category C as there is not enough information about their use in pregnancy.

Pregnancy categories

A: Controlled studies in women fail to demonstrate a risk to the fetus in the first trimester and there is no evidence of a risk in later trimesters.

B: Either animal reproduction studies have failed to demonstrate a fetal risk, but there are no controlled studies in pregnant women; or animal reproduction studies have shown adverse effect that was not confirmed in controlled studies in women in any trimester.

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C: Either studies in animals have revealed adverse effects on the fetus and there are no controlled studies in women; or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

D: There is positive evidence of human fetal risk, but the benefits from use in pregnant women may be acceptable despite the risk.

X: Studies in animals or human beings have demonstrated fetal abnormalities or there is evidence of fetal risk based on human experience or both, and the risk of the use of the drug in pregnant women clearly outweighs any possible benefits. The drug is contraindicated in women who are or may become pregnant.

The goal is to try to avoid medications as much as possible in pregnancy but, if needed, one may start with the pregnancy category. There are also reproductive drug information sites, such as Reprotox®, which will give all the available information, studies, and individual case reports for each drug as it pertains to pregnancy and breastfeeding.

Listed below are the common drugs, chemicals and exposures that are teratogenic in pregnancy and are to be avoided if possible.

  • Angiotensin-converting enzyme inhibitors (ACEIs) cause fetal renal tubular dysplasia, oligohydramnios, intrauterine growth retardation, renal failure, lack of cranial ossification

  • Warfarin causes fetal warfarin syndrome in 15-25% of exposed fetuses, including intrauterine growth retardation, developmental delay, nasal hypoplasia, microcephaly, mental retardation, skeletal abnormalities

  • Carbamazapine causes neural tube defects, microcephaly, developmental delay, intrauterine growth retardation

  • Folic acid antagonists (such as methotrexate) cause various abnormalities and increased spontaneous abortion

  • Diethylstilbestrol (DES) causes in the fetus clear cell adenocarcinoma of the vagina and cervix, vaginal adenosis, abnormalities of the cervix, uterus, and testes, and possible infertility

  • Fluoroquinolones cause arthropathy in animals, with erosion of cartilage of weight-bearing joints

  • Lithium causes congenital heart disease, often Ebstein’s anomaly

  • Non-steroidal anti-inflammatory drugs (NSAIDS) and aspirin cause premature closure of the ductus arteriosis in the third trimester

  • Phenytoin causes mental retardation, microcephaly, cardiac defects

  • Streptomycin causes cranial nerve eight damage, hearing loss

  • Testosterone causes virilization of the female and advanced genital development of the male

  • Tetracycline causes permanent yellow brown discoloration, hypoplasia of tooth enamel

  • Thalidomide causes bilateral limb deficiencies, and cardiac and gastrointestinal abnormalities

  • Trimethadione causes cleft lip and palate, intrauterine growth retardation, microcephaly, mental retardation, cardiac defects, limb and genitourinary (GU) abnormalities

  • Valproic acid causes neural tube defects especially spina bifida, and minor facial defects

  • Vitamin A and its derivatives (isoretinoin/retinoids) cause cardiovascular effects, cleft lip and palate, central nervous system defects, mental retardation, increased abortion rate

Modified from American Congress of Obstetricians and Gynecologists (ACOG) Practice Bulletin.

Chemicals and exposures
  • Cocaine causes malformations of the heart, face, genitourinary tract; microcephaly, intrauterine growth retardation; cerebral infarcts; bowel atresia

  • Lead causes stillbirths and increased abortion rate, and affects fetal central nervous system

  • Mercury causes mental retardation, cerebral atrophy, microcephaly, seizures, blindness

  • Smoking causes fetal demise, low birth rate, placental abruption

  • Heroin causes fetal withdrawal and has effects on central nervous system

  • Alcohol causes fetal alcohol syndrome, intrauterine growth retardation, mild mental retardation, behavioral problems

  • Radiation up to 5 rads in pregnancy is safe—a chest x-ray is less than one millirad; a computed tomography (CT) scan of the abdomen/pelvis is 1 rad.

Modified from ACOG Committee Opinion #282, January 2003.


These are recommendations for immunizations in pregnancy. Ideally all immunizations would be given prior to pregnancy.

  • Safe: hepatitis A, hepatitis B, influenza, meningococcus, pneumococcus, rabies, typhoid, tetanus/diphtheria/pertussis

  • Not safe: measles, mumps, polio, rubella, varicella, yellow fever (unless exposure is definite), Gardisil®

Modified from ACOG Educational Bulletin #236, April 1997.

Acceptable treatments

These are acceptable treatments for common problems in pregnancy:

  • Common cold: acetaminophen, Robitussin®, pseudoephedrine, diphenhydramine, guaifenesin, Cepacol® throat lozenges

  • Constipation: docusate, psyllium seed, Senokot®, Milk of Magnesia, polyethylene glycol

  • Environmental allergies: cetirizine, pseudoephedrine, loratadine

  • Headache: acetaminophen, Fioricet

  • Heartburn: calcium carbonate, ranitidine, famotidine, omeprazole

  • Hemorrhoids: Preparation H®, Tucks®, Anusol®

  • Nausea: vitamin B6, prochlorperazine, promethazine, metoclopramide, ondansetron

The common pitfall always in pregnancy is not to recognize a patient is pregnant. This should always be a top priority when treating female patients. It becomes particularly important when the physician wishes to prescribe a medication or procedure that is teratogenic or considered harmful in pregnancy.

No national standards or benchmarks established yet.

VI. What's the Evidence?