Barbiturates and benzodiazepines are category D and are to be avoided during pregnancy. Benzodiazepines such as diazepam (Valium), midazolam (Versed) and Lorazepam (Atavan) are implicated in the development of cleft palate, cardiac defects and inguinal hernias when prescribed for prolonged periods of time. Hydroxyzine (Vistaril) and chloral hydrate are category C drugs. Triazolam (Halcion) is a category X drug and should be avoided.
Although not rated in the FDA classification system, the use of nitrous oxide as an anxiolytic during pregnancy is questionable. It has been suggested that long-term exposure to nitrous oxide may be associated with spontaneous abortion and birth defects. It is known to effect vitamin B12 metabolism, rendering the enzyme methionine synthase inactive in the folate metabolic pathway. Methionine synthase is vital for the production of DNA, and it is recommended nitrous oxide not be administered during the first trimester of pregnancy when organogenesis occurs.
Of great concern for the safety of the pregnant female during nitrous oxide administration is the potential for hypoxia. After the first trimester of pregnancy, short-term administration of nitrous oxide to the apprehensive patient, with a minimal concentration of 50% nitrous oxide, should be safe; however consultation with the obstetrician prior to administration is recommended.15,33,37