Influence of gestational age and maternal height on fetal femur length calculations*1

Abstract

Early gestational age increases a woman's risk of having an abnormal measured:expected FL ratio, whereas short stature increases a woman's risk of having an abnormal BPD:FL ratio at later gestational ages. These findings indicate that risk assessment for fetal Down syndrome for such patients might be inaccurate. (Obstet Gynecol 2001;97:742-6.

Do parental heights influence pregnancy length?: a population-based prospective study, HUNT 2

“…If fetal size (BPD) in early second trimester also differ according to maternal height, ultrasound dating may induce a biased estimate of EDD [31]. Femur length of the fetus at 18–19 gestational weeks has been reported to correlate with maternal height, [32]maternal height is a known determinant of offspring birth weight [5,33,34],and fetal size in early second trimester is positively associated with offspring birth weight [35,36]. Thus, it is not unlikely that ultrasound in 17–19 weeks of gestation may underestimate the true gestational age of a short woman and shift the EDD to a later date due to her smaller than average sized fetus, and vice versa for taller women.…”

“…Thus, it is not unlikely that ultrasound in 17–19 weeks of gestation may underestimate the true gestational age of a short woman and shift the EDD to a later date due to her smaller than average sized fetus, and vice versa for taller women. As a result, shorter women may have more severe post-term pregnancies than taller women and may therefore be at higher risk of adverse perinatal outcomes as well [31]. Taller women, on the other hand, may risk labor inductions on false post-term indications.…”