Sonographic appearance of occipital fetal hair

The sonographic characteristics and the frequency of the presence or absence of fetal hair in the occipital region was determined from 16 weeks to 42 weeks of menstrual age. Our results suggest that the ultrasonic appearance of occipital hair is first noted at approximately 24 weeks of menstrual age and there is a progressive increase in frequency of hair presence as pregnancy approaches term. The normal ultrasonic characteristics of occipital fetal hair are described, and the differential diagnoses between normal fetal hair and malformations such as meningocele, encephaloceles, or cystic hygromas is discussed.