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 noninvasively in the fetus using ultrasound and further showed differences in reference ranges between populations.

Method: Two hundred ten singleton pregnancies were recruited at the Rosie Hospital, Cambridge, UK. A 2D ultrasound was performed between 26 and 30 weeks of 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 that 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.

Figure 1

Example of the perineum in a female fetus demonstrating the anogenital distance measurement. AGD was measured from the centre of the anus to the posterior convergence of the fourchette. The posterior convergence of the fourchette was identified by the visibility of three white lines [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 2

Example of the perineum in a male fetus demonstrating the anogenital distance measurement AGD was measured from the centre of the anus to the base of the scrotum. The scrotum was identified by the visibility of the scrotal sack [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 3

Bland‐Altman plot observing intraobserver variability

Figure 4

Bland‐Altman plot observing interobserver variability

Figure 5

A scatterplot of raw AGD measures split by males fetuses and female fetuses between 25 and 31 weeks of gestation. Mean linear regression lines have been plotted by sex [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 6

A scatterplot of matched raw AGD measures taken in both UK and Israel populations by sex between 26 and 31 weeks of gestation. Mean linear regression lines have been plotted by sex [Colour figure can be viewed at wileyonlinelibrary.com]