Fetal isolated short femur in the second trimester and adverse pregnancy outcomes

This study aims to evaluate the association of isolated short femur (ISF) in the second trimester ultrasound with adverse pregnancy outcomes.

All obstetric scans between 16 and 24 weeks of gestation from 1 January 2006 to 1 June 2012 were retrospectively evaluated. Multiple pregnancies, major congenital or chromosomal anomalies and subjects with incomplete outcome data were excluded. Femur length (FL) measurement from the earliest scan of singleton pregnancies was selected. An ISF was defined as a FL less than the tenth percentile in a fetus with an abdominal circumference greater than or equal to the tenth percentile. The primary outcomes were small for gestational age (SGA), birth weight below the third and fifth percentiles, low birth weight (LBW), preterm birth (PTB) and preeclampsia (PE). A 5-min Apgar score of less than 7 and a neonatal intensive care unit admission were secondary outcomes.

Of the 4992 eligible fetuses, 312 (6%) had an ISF. Mothers in the short femur group were shorter and had a lower prepregnancy and delivery weight than the group with normal FL (p < 0.05). Multiple logistic regression revealed a significant increase in birth weight below fifth percentile, SGA, LBW infants and PTB (<32, <34 and <37 weeks) in the ISF group (p < 0.05). The incidence of PE was similar in both groups.

Isolated short femur in the second trimester increases the risk of LBW, SGA and PTB, but not of PE.