Fetal anogenital distance using ultrasound.

Abstract

Objective: This study measured anogenital distance (AGD) during late second/early third trimester of pregnancy to confirm previous findings that AGD can be measured non-invasively in the fetus using ultrasound, and further showed differences in reference ranges between populations.

Method: 210 singleton pregnancies were recruited at the Rosie Hospital, Cambridge, UK. A 2D ultrasound was performed between 26-30 weeks pregnancy. AGD was measured from the centre of the anus to the base of the scrotum in males, and to the posterior convergence of the fourchette in females.

Results: A significant difference in AGD between males and females (p<.0001) was found, replicating previous results with a significant correlation between estimated fetal weight (EFW) and AGD in males only (p=.006). A comparison of AGD using reference data from an Israeli sample (n=118) and our UK sample (n=208) showed a significant difference (p<.0001) in both males and females, after controlling for gestational age (GA).

Conclusion: Our results confirm AGD measurement in utero using ultrasound is feasible. In addition, there are strong sex differences, consistent with previous suggestions that AGD is influenced by prenatal androgen exposure. AGD lengths differ between the UK and Israel, therefore population-specific normative values may be required for accurate clinical assessments.