Predictive value and reference ranges of anogenital distance for determining fetal gender in the first trimester: A retrospective cohort study

Abdulrahman M. Alfuraih; Samiah A. Alotaiby; Mohammed J. Alsaadi; Hanifa A. Bukhari; Ali M. Aldhebaib; Rafat S. Mohtasib

doi:10.15537/smj.2021.42.10.20210468

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Figure 1
- Examples of anogenital distance measurements for A) male and B) female 12-week-old fetuses.
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Figure 2
- A bar chart of anogenital distance (mm) against fetal gestational age by gender. CI: confidence interval
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Figure 3
- A scatter plot of anogenital distance measurements with interpolated means for male and female fetuses.

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Table 1

- Main maternal and fetal characteristics

Characteristics	Male at birth (n=172)	Female at birth (n=141)	Total (n=313)
Maternal age (years)	31.8 (5.1)	31.8 (5.9)	31.8 (5.3)
Gestational age (days)	87.9 (4.7)	87.7 (4.8)	87.8 (4.8)
Birth weight (g)	2,945 (539)	3,000 (509)	2,970 (526)
Crown-rump length (mm)	60.0 (9.3)	59.8 (9.5)	59.9 (9.4)
Fetal heart rate (bpm)	135.7 (10.8)	136.0 (10.3)	135.9 (10.6)

Numbers in parentheses represent standard deviations.

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Table 2

- Mean anogenital distance values in each gestational week.

Week of gestation	Female	Male	Female at birth	Male at birth	Differences in mean and percentage	P-value
11 weeks	33	36	4.82 [4.50, 5.14]	5.66 [5.34, 5.98]	0.84 [0.39, 1.28] (17.4%)	<0.001
12 weeks	67	85	5.77 [5.54, 6.05]	6.74 [6.52, 6.96]	0.97 [0.65, 1.29] (16.8%)	<0.001
13 weeks	41	51	6.99 [6.60, 7.38]	7.70 [7.37, 8.04]	0.71 [0.20, 1.21] (10.2%)	0.006
Total	141	182	5.92 [6.70, 6.14]	6.80 [6.61, 7.00]	0.88 [0.59, 1.17] (14.8%)	<0.001

Data between square brackets represent the 95% confidence intervals.

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Table 3
- Mean anogenital distance values in first trimester fetuses amongst different populations.
Population Female (mm) Male (mm) Best AGD cutoff (mm)
Saudi 5.92 (1.32) 6.80 (1.26) 6.00
French⁷ 4.20 (0.95) 6.00 (1.27) 4.80
Persian⁸ 4.30 (0.81) 5.14 (0.85) 4.50
Turkish⁹ 3.60^* 5.10^* 4.80
Numbers in parentheses represent the standard deviations.
↵*The standard deviations were not reported. AGD: anogenital distance

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Appendix 1

- Normal anogenital distances reference ranges for each gestational week: 2.5th to 97th centiles.

Centile	11 weeks	12 weeks	13 weeks
Male
2.5^th	3.82	4.78	5.36
5^th	4.12	5.10	5.73
10^th	4.46	5.46	6.17
25^th	5.03	6.07	6.89
50^th	5.66	6.74	7.70
75^th	6.29	7.41	8.51
90^th	6.86	8.02	9.23
95^th	7.20	8.38	9.67
97.5^th	7.50	8.70	10.04
Female
2.5^th	3.06	3.84	4.59
5^th	3.35	4.15	4.97
10^th	3.67	4.51	5.42
25^th	4.22	5.11	6.17
50^th	4.83	5.78	7.00
75^th	5.43	6.44	7.83
90^th	5.98	7.04	8.58
95^th	6.31	7.40	9.02
97.5^th	6.59	7.72	9.41

All readings are in millimeters.

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Appendix 2

- Predictive performance of the AGD cutoffs.

Gestation age	AGD cutoff (mm)	Acc	Sens	Spec	PPV	NPV	+LH	-LH	AUC	P-value
11 weeks	>5.10	68%	72%	64%	68%	68%	2.00	0.50	0.738	0.001
12 weeks	>6.07	70%	74%	64%	72%	66%	2.06	0.49	0.752	<0.001
13 weeks	>7.17	64%	69%	59%	67%	60%	1.68	0.59	0.646	0.017
Total	>6.00	65%	72%	56%	67%	62%	1.64	0.61	0.686	<0.001

A positive result indicates the identification of male gender. Acc: Accuracy, Sens: sensitivity, Spec: specificity, PPV: positive predictive value, NPV: negative predictive value,+LR: positive likelihood ratio, –LR: negative likelihood ratio, and AUC: area under the curve