What primary factor helps determine if intrauterine growth restriction is symmetrical or asymmetrical?

The primary factor that helps determine if intrauterine growth restriction (IUGR) is symmetrical or asymmetrical is head circumference. In cases of symmetrical IUGR, all body measurements, including head circumference, length, and weight, are proportionately reduced, indicating that the entire growth process has been affected uniformly. Conversely, in asymmetrical IUGR, the head circumference is often preserved while weight and length may be diminished. This pattern suggests that the brain, a priority for fetal resources, has grown relatively normally, while the body has not received adequate nutrition or oxygen in the later stages of pregnancy. Therefore, measuring head circumference is crucial because it provides insight into the type of growth restriction present, allowing healthcare providers to assess the severity and potential underlying causes more accurately.