Fetal foot length throughout gestation: a nomogram

Abstract

Objective: There are certain situations in obstetric ultrasound such as hydrocephalus, anencephaly, short limb dysplasia, where traditional biometric values cannot be used to assess gestational age. In these situations, we have to use other parameters for the accurate assessment of gestational age. One of the useful parameters is foetal foot length because it is easily accessed and measured easily. Objective of our study was to create a nomogram of fetal foot length (FtL) throughout gestation. Methods: It was a longitudinal prospective study of patients between 16 and 40 weeks of gestation. Inclusion criteria consisted of well-establisheddates (consistent with early ultra sound), singleton, non-anomalous fetuses, and intact amniotic membranes. Sonographic measurements included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femurlength (FL). For every case, the average of three separate measurements of FtL was used. The mean, percentiles and standard deviations for FtL were calculated at 4 weeks intervals starting from 16th week to 40th week. Pearson's correlation coefficient and associated P-values for the relationships between FtL and other biometric measurements were calculated. The data were compared to anomogram of the FtL generated from previous published studies. Results: Longitudinal foot length measurements obtained in 50 antenatal women were studied. Nomograms were constructed using Mean ± 2 SD and Percentiles (5th, 50th and 95th centiles). There was strong correlation between foot length measurements and gestational age and could be linearly predicted (Foot Length =-14.02 + 2.3609 * Gestational Age, R2 = 0.97, P<0.001). Foot length had better correlation with gestational age compared to other sonologic parameters such as BPD, HC, AC and FLwith Pearson correlation values of 0.94, 0.936, 0.951, 0.96, respectively (all p<0.001). Conclusions: We constructed a nomogram for fetal foot length at various gestation intervals for the local population. There was a linear relationship and good correlation between foot length and other biometric measurements. These nomograms may be useful to assess gestational age when duration of pregnancy is unknown.