How can I differentiate between symmetrical and asymmetrical IUGR during clinical assessment?

Symmetrical and asymmetrical intrauterine growth restriction (IUGR) can be differentiated during clinical assessment primarily through ultrasound biometric measurements and clinical history.

Symmetrical IUGR is characterized by a proportionate reduction in all fetal measurements, including head circumference, abdominal circumference, and femur length, indicating early onset growth restriction often due to intrinsic fetal factors such as chromosomal abnormalities or infections.

In contrast, asymmetrical IUGR typically presents with a relatively normal head circumference but a disproportionately small abdominal circumference, reflecting a late-onset growth restriction usually caused by placental insufficiency where the fetus redistributes blood flow to preserve brain growth at the expense of the abdomen.

During clinical assessment, symphysis fundal height measurements plotted on growth charts can raise suspicion of IUGR, prompting ultrasound evaluation to assess fetal biometry and growth patterns.

Ultrasound assessment should include multiple biometric parameters to distinguish symmetrical from asymmetrical growth restriction by comparing head and abdominal circumferences and femur length.

Additional Doppler studies, such as umbilical artery flow, may assist in assessing placental function and fetal wellbeing, particularly in asymmetrical IUGR cases.

Therefore, differentiation relies on detailed ultrasound biometric analysis rather than clinical examination alone, supported by serial fundal height measurements and clinical risk assessment.

This approach aligns with the NICE antenatal care guideline recommendations to use symphysis fundal height measurements after 24 weeks and to offer ultrasound scans for fetal growth and wellbeing if growth restriction is suspected.