A 5-hour-old boy is evaluated in the nursery for minimal right arm movement. He was born at 39 weeks gestation to a 37-year-old multigravida via vaginal delivery complicated by difficulty extracting the shoulders. Review of medical records reveals a maternal history of hypertension and recreational marijuana use. The mother missed most of her prenatal appointments. The patient's birth weight is 4.5 kg (9 lb 14 oz). Vital signs are normal. Examination shows a plethoric infant with crepitus and irregularity over the right clavicle. Moro reflex is absent on the right extremity. Bilateral biceps and grasp reflexes are intact and symmetric. Which of the following risk factors predisposed the infant to this complication?

Question

A 5-hour-old boy is evaluated in the nursery for minimal right arm movement.  He was born at 39 weeks gestation to a 37-year-old multigravida via vaginal delivery complicated by difficulty extracting the shoulders.  Review of medical records reveals a maternal history of hypertension and recreational marijuana use.  The mother missed most of her prenatal appointments.  The patient's birth weight is 4.5 kg (9 lb 14 oz).  Vital signs are normal.  Examination shows a plethoric infant with crepitus and irregularity over the right clavicle.  Moro reflex is absent on the right extremity.  Bilateral biceps and grasp reflexes are intact and symmetric.  Which of the following risk factors predisposed the infant to this complication?

Quizplus · Accepted Answer

11ec25c8_d70a_5c56_bc81_b32a1630bd47_MD0003_00 This neonate's birth weight is consistent with macrosomia (fetal weight ≥4 kg [8 lb 13 oz]), and his physical examination findings reflect complications of shoulder dystocia. Fetal hyperglycemia (eg, due to untreated maternal diabetes mellitus) is the most common underlying risk factor. Mild maternal insulin resistance is a physiologic process of pregnancy that facilitates the diffusion of glucose across the placenta for fetal growth. However, excessive maternal hyperglycemia (ie, gestational or prepregnancy diabetes mellitus) results in fetal hyperglycemia, which increases fetal pancreatic insulin secretion, causing fetal hyperinsulinemia. Excessive production of fetal insulin, an anabolic hormone, leads to macrosomia with disproportionate growth and fat accumulation over the shoulders and abdomen. As a result, the shoulders can become impacted in the maternal pelvis, resulting in shoulder dystocia, an obstetric emergency. Potential complications of shoulder dystocia include clavicle fracture, brachial nerve palsy, perinatal asphyxia, and hypoxic encephalopathy. Maternal hyperglycemia can also lead to neonatal polycythemia and plethora as well as postnatal hypoglycemia. Fetal hyperglycemia and hyperinsulinemia likely contributed to this patient's macrosomia, plethora, and shoulder dystocia with resultant clavicle fracture (eg, crepitus, asymmetric Moro reflex). (Choices A, B, D, and E) Congenital infections; fetal aneuploidy; and maternal hypertension and substance abuse are all associated with fetal growth restriction and small-for-gestational-age infants (eg, birth weight <10th percentile). Fetal growth restriction occurs due to the compromise of placental function and a decreased ability to transport oxygen and other nutrients from mother to fetus. Decreased placental oxygen transfer can lead to fetal hypoxemia, in which the fetus attempts to maintain oxygenation by suppressing growth and metabolism. This infant has macrosomia rather than growth restriction. (Choice F) In addition to fetal growth restriction, maternal tobacco use can cause irritability and hypertonicity in newborns, neither of which are seen in this macrosomic patient. Educational objective: Excessive maternal hyperglycemia causes fetal hyperglycemia and hyperinsulinemia. Neonates may be macrosomic, increasing the risk of shoulder dystocia and its complications (eg, brachial nerve palsy, clavicle fracture). References: Pregnancy week at delivery and the risk of shoulder dystocia: a population study of 2,014,956 deliveries. (http://www.ncbi.nlm.nih.gov/pubmed/24020942) Gestational diabetes mellitus and macrosomia: a literature review. (http://www.ncbi.nlm.nih.gov/pubmed/26045324)

A 5-Hour-Old Boy Is Evaluated in the Nursery for Minimal