International standards for early fetal size and pregnancy dating based on ultrasound measurement of crown–rump length in the first trimester of pregnancy
Papageorghiou AT., Kennedy SH., Salomon LJ., Ohuma EO., Cheikh Ismail L., Barros FC., Lambert A., Carvalho M., Jaffer YA., Bertino E., Gravett MG., Altman DG., Purwar M., Noble JA., Pang R., Victora CG., Bhutta ZA., Villar J.