I am not a great fan of ultrasound measurements, when I was pregnant with my daughter, they scanned me at 34 weeks as my waters had gone and they told me her abdomen was swollen and they didnt know why and that I may have a still birth, hse was born 3 days later perfectly healthy and absoloutley nothing wrong with her abdomen. with my son they scanne me every 2 weeks for 30 weeks as they said his head was excessively large, they were planning c section as thought to big to pass thorugh birth canal. Anyways I had natural labour and his head was on the normal 50th centile on the birth chart. Also my friend was told her son had short thigh bones and did not know what that meant again he was born perfectly healthy. I know ultrasounds are great at detecting birth defects however they are not 100%. Take it easy and try not to worry you will soon meet your baby, Take care
if baby is happy and healthy i would not worry too much. what did the doctor say? is he worried? if not then dont panic, enjoy the rest of your pregnancy