A 32-year-old woman visits her obstetrician for her first prenatal appointment at 10 weeks of gestation. She reports that she has continued taking valproic acid for her epilepsy but is concerned after reading about its potential risks during pregnancy. She has not taken any folic acid supplements and reports no significant health issues so far. The obstetrician explains that valproic acid is a known teratogen, particularly during the critical window of fetal heart development. During which gestational weeks is the fetal heart most susceptible to teratogens?
