Q. A 35-year-old woman comes for her initial prenatal visit. Yesterday, she performed a home pregnancy test that turned positive. She currently has no bothersome symptoms except for nausea. The patient's medical history is significant for multiple manic episodes. Her current medications are lithium and multivitamins. The patient's vital signs are normal. Her basic metabolic profile and lithium level are normal. Which of the following congenital defects is of concern in the offspring of the above patient?