Birthweight of twins are lower than singletons. The moment at which stops may define the best follow-up. Retrospective study of ultrasound weight estimation in twins. Only dichorionic and monochorionic- biamniotic twins were included. Triplets, monoamniotic twins, severe malformations, fetus with aneuploidies, TRAP and TTTS were excluded. Only scans with alive twins at ultrasound were included. Seven GA study groups were defined as 18-20, 21-23, 24-26, 27-29, 30-32, 33-35 and 36-38. Estimated fetal weight Z-score was compared to normal, at different GA groups, with single sample T-test. 666 scans from 198 twins were considered for analysis. 69 were Monochorionic. Twins had lower weight than singletons and there was a significant reduction after 34 weeks of gestational age (z score -0.64, 95%CI -0.79 to -0.48, p<0.001. Before 24 weeks is difficult to interpret because reference charts are weaker at this GA and most of these fetuses continued normally to the next group. Twins growth falls after 34 weeks. Close follow-up until term is warranted. Supporting information can be found in the online version of this abstract Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.