Aim (1) To asses the accuracy of estimated fetal birth weight (EFBW) by ultrasound growth scan (USS) in multiple pregnancy. (2) To identify whether USS EFBW overestimate or underestimate actual birth weight. (3) An acceptable standard of 250 g difference between the USS weight and the actual birth weight was agreed.

Material and Methods A retrospective cohort study using patient's hospital notes. 28 women with twin pregnancy who delivered at Cumberland Infirmary in 2009 were included.

Using customised growth charts (Perinatal Institute) the EFBW for the growth scan closest to the birth date was plotted. By following that centile the EFBW at the time of delivery estimated. The difference between this EFBW and the actual weight was calculated.

Results 71% of the estimated birth weights by USS were within 250 g of the actual birth weight. 22% of the EFBW by USS were within 50 g of the actual birth weight. 70% of the USS estimated birth weights were larger than the actual birth weight and 30% were smaller.

Conclusion This is commoner for birth weight to be overestimated by USS than underestimated. 71% of the USS estimated birth weights are within the agreed standard of 250 g difference within the actual birth weight.