J Child Neurol 4 Suppl: S32-S40, 1989. doi: 10.1177/0883073889004001s07 Diagnosis Prenatally, ultrasound Postnatally, physical examination, including measurement of head circumference and cranial MRI Genetic testing Prenatally, the diagnosis of macrocephaly sometimes is made with routine ultrasonography done in the late second or early third trimester.