Crown-rump length measured in the early first trimester as a predictor of low birth weight.

The aim of this study is to assess the association between crown-rump length (CRL) measured before the 10th gestational week and birth weight. Results from 316 transvaginal ultrasonography scans at the 46th, 53rd, 60th, 67th, and 74th days of pregnancy were compared in low birth weight (LBW) versus normal birth weight groups. A positive correlation between CRL and birth weight was observed when CRL was measured at days 60, 67, and 74. CRL measured on the 67th day of pregnancy was significantly smaller in the LBW group than in the normal birth weight group. A cut-off value of CRL=26.5 mm measured at day 67 has the highest power to predict LBW.