The nurse is caring for a patient who gave birth to an infant with a congenital heart anomaly. The patient asks the nurse when such anomalies occur during development. Which response by the nurse is most accurate?

A. "It depends on what caused the defect" is incorrect because while risk factors may vary, the critical period for heart development is well-established. Heart formation occurs during a specific window in fetal development, regardless of the cause. B. "They usually occur in the first 2 weeks of development" is incorrect because the first two weeks after fertilization (the pre-embryonic period) involve cellular proliferation and implantation, not organ formation. Heart structures have not yet developed during this period. C. "We don't really know when such defects occur" is incorrect because the timing of congenital heart development is well-documented. Most defects arise during a defined embryonic period. D. "They occur between the third and eighth weeks of development" is correct. The heart begins forming in the third week after fertilization, and most major structural cardiac development occurs by the eighth week. Exposure to teratogens, maternal illnesses, or genetic factors during this period can lead to congenital heart defects.