A patient who experienced a miscarriage at 10 weeks is concerned about whether a one-time exposure to a high dose of a recreational drug at 4 weeks post-LMP could be related. Using application of knowledge about timing and teratogens, which response is most accurate?

• A. A single exposure at 4 weeks post-LMP could only cause genetic changes but not structural defects or pregnancy loss, so the miscarriage must have had a purely chromosomal origin unrelated to environmental factors.
• B. It is possible that exposure to a teratogen early in gestation contributed to miscarriage, because exposures during early developmental stages can both cause birth defects and increase risk of spontaneous abortion before 20 weeks.
• C. It is impossible that the drug exposure was involved because teratogens only affect the fetus after 20 weeks of gestation; early exposures are harmless.
• D. If the exposure occurred after implantation it cannot affect development at all, and miscarriage is always due to maternal nutrition alone rather than toxic exposures.

Answer: (B)