my last scan was at 36 1/2 weeks to check bubs size. the tech was able to identify all of his body part sizes and the fluid around him and yes also that he was still boy!! obviously you cann only see parts of the bady as they are too big by then to see them as a whole. at this last scan he was estimated to weigh 5pd 10oz and a week and a half later he was born 5pd 5oz. i think it all just depends on the accuracy of the measurements taken at the time.