International Journal of Clinical Obstetrics and Gynaecology

Congenital hyperinsulinism (CHI) is a rare genetic disorder of pancreatic ?-cell function and the leading cause of persistent hypoglycemia in infancy. While most cases present postnatally, in utero hyperinsulinism can promote excessive fetal growth, even in the absence of maternal diabetes.
We report a case of a 23-year-old primigravida with an uncomplicated pregnancy who delivered a macrosomic infant (6175 g) complicated by severe shoulder dystocia following vacuum assisted delivery (VAD). The infant was stillborn after failed maneuvers and surgical extraction. Histopathological examination revealed islet cell hypertrophy and hyperplasia, and genetic testing identified an ABCC8 mutation shared by both the mother and the fetus.
This case illustrates autosomal dominant ABCC8-related CHI manifesting as fetal macrosomia in nondiabetic pregnancies. The findings highlight the potential for monogenic hyperinsulinism to drive fetal overgrowth and obstetric complications, such as shoulder dystocia. Recognition of genetic causes of fetal macrosomia is essential for individualized obstetric management, anticipatory delivery planning, and genetic counselling.