- Half of pregnancies in the United States are unplanned.
- Many women of childbearing age have medical conditions that require ongoing or intermittent treatment with medications.
- A 2010 study by a VA physician and clinical pharmacist found that 49% of women Veterans received a prescription for a medication that increases the risk for birth defects in humans; 44% of these women had no documented family planning services.
- Ask patients about their use of prescription medicines, non-prescription medicines and dietary supplements.
- Risk/Benefits discussions about medication-related risk must occur before pregnancy occurs.
- In the embryo, development of major organ systems begins 2 to 3 weeks after conception, before a woman may know she is pregnant.
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Critical Stages of Embryonic Development
Adapted from a presentation by Dr. Atrash (CDC, 2009) During embryonic development, an organ or organ system is most vulnerable to the teratogenic effects of medications or other exposures when it is undergoing the most rapid and extensive change and growth. Weeks of gestation or pregnancy are counted from the first day of the last menstrual period even though conception does not occur until about 14 days later (may range from 7 to 21 days).
At a gestational age of 4 to 5 weeks, which is 2 to 3 weeks after conception occurs, a pregnant woman misses her menstrual period. She may become aware of her pregnancy at this time or may not find out that she is pregnant until a later date. On average, women enter prenatal care at about 11 to 12 weeks gestation, which is close to the end of the first trimester.
The graph illustrates the gestational weeks during which different organs and organ systems undergo most of their structural formation. Maturation of all organs continue throughout pregnancy, but the following time periods are the critical stages of structural development when the organs are most vulnerable to teratogen-associated changes in structure and function:
- Central nervous system: 5 to 8.5 weeks gestation
- Heart: 5.5 to 8.5 weeks gestation
- Arms: 6.5 to 10 weeks gestation
- Eyes: 6.5 to 10.5 weeks gestation
- Legs: 6.5 to 10 weeks gestation
- Ears: 6.5 to 11.5 weeks gestation
- Teeth: 8.5 to 11 weeks gestation
- Palate: 8.5 to 11.5 weeks gestation
- External genitalia: 9.5 to 12 weeks gestation.
FDA Pregnancy Categories
- The FDA pregnancy category letter alone is not enough.
- Read the pregnancy subsection of labeling for each medication and/or the REPROTOX® summary (see Resource Section).
- The FDA pregnancy categories describe only general differences in the reproductive risk of medications based on the types of data available (animal vs. human and studies vs. case reports) and reproductive outcomes. Some categories consider treatment benefit as well as risk.
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FDA Pregnancy Categories
- Category A: Well controlled studies in human pregnancy show no increased risk to the fetus.
- Category B: Animal studies show no increases risk to the fetus OR Animal studies show an increased risk to the fetus but well controlled human studies do not.
- Category C: Animal studies show an increased risk to the fetus and there are no well controlled studies in human pregnancy OR There aren't any animal studies or well controlled human studies.
- Category D: Data from human pregnancy show increased fetal risk. Data may be from sources with various strengths of evidence (clinical trials, cohort or case control studies, case reports). Potential benefits from use of the drug may be acceptable despite the potential risks.
- Category X: Use contraindicated during pregnancy. Animal or human studies or human adverse event reports demonstrate fetal risk AND The risk of using the drug during pregnancy clearly outweighs any possible benefit.