Indications for a third trimester ultrasound include assessment of fetal growth and well-being due to fetal anomaly, maternal disease, obstetric complications, previous poor obstetric history or to assess growth in multiple pregnancies. This is usually done by measuring fetal biometry, liquor volume and umbilical artery (UA) Dopplers. The fetal biometry measured includes biparietal diameter, head circumference, abdominal circumference and femur length. From these parameters, estimated fetal weight is calculated which is compared with expected weight for gestational age. Appropriate growth is determined by first determining gestational age and then comparing biometric parameters with normal range charts There are two types of abnormal growth, small for gestational age (SGA) and large for gestational age (LGA). Ultrasound is the main tool for recognising these conditions. Due to the error inherent in estimating fetal weight, a combination of factors is usually assessed to try and determine a fetus that is pathologically grown. A SGA fetus is usually recognised by biometry below the 10th percentile, decreased liquor volume and an increased UA Doppler. Other fetal Dopplers such as middle cerebral artery and ductus venosus can then be performed to help assess fetal status. A LGA fetus demonstrates biometry above the 90th percentile often with increased liquor volume and normal UA Dopplers. The third trimester scan can also be used to assess placental and fetal position. It is important to remember that ultrasound measurements should not be viewed in isolation as integrated fetal testing can reduce perinatal morbidity and mortality.