The infant in the question stem is likely an infant of a diabetic mother (IDM). Infants of diabetic mothers are at risk for a number of complications, including caudal regression syndrome and hypoglycemia. Persistent elevation of insulin leads to hypoglycemia shortly after birth in infants of diabetic mothers.
In utero, a fetus of a diabetic mother is exposed to inappropriately high levels of glucose. The fetus responds with hyperinsulinemia, triggering increased growth of the fetus. Macrosomia (large size for gestational age) results, as does altered development of organs including impaired lung maturation. Caudal regression syndrome, also known as sacral agenesis, in which malformation of the caudal spine results in lower extremity paralysis and weakness, is an important complication of maternal diabetes to know for the USMLE Step 1.
Lin et al. discuss the screening guidelines for gestational diabetes. In the U.S. the most common method of testing for gestational diabetes would be by an oral 50-gram 1 hour glucose challenge test somewhere between 24-28 weeks gestation. If the result is abnormal (>140), the patient would then undergo an oral 100-gram 3 hour glucose challenge test. Two or more abnormal values on this test would render the patient as a gestational diabetic. Treatment would include diet and lifestyle modifications and sometimes medication implementation (insulin or oral hypoglycemic agents).
Hay reviews the care of the infant of a diabetic mother. IDMs are at risk for a plethora of complications not limited to preterm birth, macrosomia, asphyxia, respiratory distress, hypoglycemia, and congenital anomalies. IDMs tend to have an increased likelihood of obesity, diabetes, and cardiovascular disease evidenced in later life. Caring for these infants includes ensuring adequate cardiorespiratory adaptation at birth, tending to various birth injuries (such as a shoulder dystocia), monitoring and maintaining appropriate glucose levels, and close observation for other complications.
Illustration A depicts a chart reviewing the symptoms often seen in neonatal hypoglycemia. Illustration B is an anterior/posterior radiograph of a child with caudal regression. Note the absent sacral vertebrae, hypoplastic pelvis, and classic "frog-leg" position of the lower extremities.
Answer 1: Infants born to diabetic mothers would be expected to have hyperinsulinemia due to the high level of glucose transferred to the infant from the mother.
Answer 2: The infant described in this question may have initially had hyperglycemia at the time of birth, but the persistent elevation in insulin has now resulted in this infant becoming hypoglycemic. Hypoglycemia is a counterintuitive yet important complication of infants born to diabetic mothers.
Answer 4-5: Infants of diabetic mothers are more likely to be hypocalcemic and hypomagnesemic. The hypocalcemia may result from decreased parathyroid hormone production, an associated complication in IDM. The hypomagnesemia may result from maternal hypomagnesemia secondary to urinary loss of magnesium in diabetes.
Lin KW, Sessions CK. Screening for gestational diabetes mellitus. Am Fam Physician. 2009 Jul 15;80(2):185.
PMID:19621860 (Link to Abstract)
Hay WW Jr. Care of the infant of the diabetic mother. Curr Diab Rep. 2012
PMID:22094826 (Link to Abstract)
USMLE World Step 1 QBank Question #1684. Copyright © USMLEWorld, LLC 2012