A 31-year-old woman presents to her obstetrician for her first prenatal visit after having a positive home pregnancy test 1 week ago. Her last menstrual period was 8 weeks ago. The patient has a medical history of type 1 diabetes mellitus since childhood and her home medications include insulin. Her hemoglobin A1c 2 weeks ago was 13.7%. At that time, she was also found to have microalbuminuria on routine urinalysis. Her primary care provider prescribed lisinopril but the patient has not yet started taking it. The patient’s brother is autistic but her family history is otherwise unremarkable. Her temperature is 98.6°F (37.0°C), blood pressure is 124/81 mmHg, pulse is 75/min, and respirations are 14/min. A physical exam is unremarkable. This fetus is most likely at increased risk for which of the following complications?
Neonatal hyperglycemia
Neural tube defect
Oligohydramnios
Post-term delivery
Neural tube defect
This patient has type 1 diabetes mellitus and presents in early pregnancy with a markedly elevated hemoglobin A1c, suggesting poor glycemic control. Poor glycemic control increases the risk of a neural tube defect in the fetus.

Infants of diabetic mothers (IDM) are at increased risk of many congenital malformations as well as postnatal complications. These risks are more likely if there is poor maternal glycemic control, especially in the periconceptional period. Poorly controlled hemoglobin A1c and microalbuminuria on urinalysis indicate long-standing poor glycemic control and indicate a poor prognosis. The most common anomalies in IDM are cardiovascular defects such as septal defects and transposition of the great arteries as well as neural tube defects such as anencephaly and spina bifida. Sacral agenesis, or a poorly developed caudal spine and spinal cord, as well as small left colon syndrome due to a meconium plug, are other common malformations seen in IDM. General complications in IDM include prematurity, intrauterine growth restriction or macrosomia, and miscarriage. Risk is minimized by tight glycemic control throughout pregnancy.

Dean et al. summarize the evidence surrounding micronutrients and obesity in pregnancy. They found that patients with diabetes had a higher risk of having infants with a neural tube or a congenital heart defect. They recommend using folic acid supplementation in all patients to reduce the risk of neural tube defects.

Incorrect Answers:
Answer A: Aneuoploidy risk is not increased in IDM. This complication is associated with advanced maternal age. This patient is at baseline risk since she is below the “advanced maternal age” cutoff of 35 years. Some of the values used in aneuploidy screening (maternal serum alpha­fetoprotein, estriol, and inhibin A) are generally lower in women with diabetes. Guidelines specific to this patient population should be used for the aneuploidy screen so as to avoid false positive results.

Answer B: Neonatal hyperglycemia is not seen in IDM. Patients may experience hypoglycemia. This is due to the crossing of glucose from the mother to the fetus via the placenta and subsequent hyperinsulinemia and ß-cell hyperplasia from the fetus. After delivery, the high insulin levels cause hypoglycemia because there is no longer an overabundant source of glucose. Hyperglycemia in infants is much less common and can be due to glucose infusion or sepsis.

Answer D: Oligohydramnios is not specifically associated with maternal hyperglycemia. Instead, patients may experience polyhydramnios. The mechanism for increased amniotic fluid is unclear, though some speculate that fetal hyperglycemia results in polyuria and thus polyhydramnios. Severe oligohydramnios can cause pulmonary hypoplasia and clubfoot as well as cord compression, while polyhydramnios is associated with cord prolapse, placental abruption, and prematurity.

Answer E: Post-term delivery occurs after 42 weeks gestation. Maternal diabetes typically causes prematurity. Post-term delivery is associated with fetal malnutrition, hypoxemia, and oligohydramnios due to suboptimal functioning of the placenta. The risk of meconium aspiration increases as gestational age increases. Induction of labor is generally performed at 42 weeks to avoid these complications.

Bullet Summary:
Maternal hyperglycemia from diabetes mellitus is associated with congenital heart defects, neural tube defects, and small left colon syndrome.