Anogenital distance (AGD) is an upcoming anthropometric parameter and is a marker of genital development in humans, around 8-14 weeks of gestation [1]. It is an indicator of the hormonal milieu around the fetus in pre-natal life. Higher exposure to androgen results in longer AGD at birth, whereas, exposure to anti-androgens results in shorter AGD; which implies it has a positive association with androgen levels. Short perineum has been correlated with an increased risk of perineum trauma, episiotomy and pelvic organ prolapse in long term [2,3]. Almost 85% women suffer perineal trauma during vaginal birth, which can have long term consequences. Anogenital distance (AGD) is a novel useful parameter for prediction of perineal tears during vaginal delivery.  We hypothesized that short AGD  increases the possibility of sustaining perineal tears during vaginal delivery. The aim of present study was to assess the role of Maternal Anogenital Distance measurement in predicting the subsequent occurrence of perineal tears during vaginal delivery. The objectives were to determine the a) Accuracy and cut-off value of Anogenital distance (AGDac & AGDaf) measurement in predicting the occurrence of perineal tears in vaginal delivery. AGDac is measured from the anterior clitoral surface to the centre of anus. AGDaf is measured from posterior fourchette to the centre of anus; b) Risk factors for perineal tears such as induction of labor, fetal malposition, prolonged 2nd stage, neonatal birth weight, head circumference, etc ; c) Pelvic Floor Distress Inventory (PFDI-20) and pelvic floor muscle strength (OXFORD grading) at 6 weeks postpartum.

In an observational case-control study, primigravida at ≥37 weeks were recruited in early labour. Ethical clearance was obtained from the institutional ethical committee for human research and informed consent was taken from the subjects. Cases were subjects who suffered ≥ 2nd degree perineal tears during vaginal delivery (n=82) and controls had intact perineum or upto 1st degree tears(n=90). Anthropometric measurements such as AGDac {anus to clitoris distance} and AGDaf {anus to fourchette distance} were done using digital vernier callipers and labour parameters like fetal position, duration of the second stage, induction of labour, birth weight etc. were noted. Receiver Operator Curve curves were plotted to obtain cut-off values AGDac and AGDaf for predicting ≥2nd degree perineal tears. [Figure 1] Considering mean & standard deviation of anogenital distance (AGDac) as 93.1(9.4) mm in case group and 97.8(10.2) mm in control group; to estimate this difference in mean value at alpha =5% and power= 80%, a sample of 70 cases in each group was required. With an estimated loss to follow up of 10%, we decided to recruit at least 80 cases and 80 controls. All the quantitative and qualitative parameters were compared by unpaired t-test and chi-square test respectively. Logistic regression analysis was done to obtain the risk factors for the likelihood of perineal tears. p value <0.05 was considered significant.

Demographic characteristics such as age, socioeconomic status, religion, education and BMI were comparable between cases and controls. The mean AGDac was 75.99+3.43mm in cases and 77.05+2.62mm in controls which was statistically significant with p value of 0.029, suggesting cases had shorter AGDac than controls. The mean AGDaf was 33.50+1.65mm in cases and 34.52+1.25mm in controls which was highly statistically significant with p= 0.001, suggesting cases had much shorter AGDaf as compared to controls.

It was observed that second degree perineal tear was the most common perineal outcome during vaginal delivery in cases. Episiotomy is included in the second degree perineal tears. Majority of women were given episiotomy i.e., 69/80 (86.25%) while 1 (1.25%) woman had cervical tear along with episiotomy. Third or fourth degree perineal tear (OASIS) occurred in 7/80 (8.75%) women and 3 (3.75%) women suffered  isolated cervical or paraurethral tears.

AGDaf had better sensitivity for prediction of ≥ 2nd degree perineal tears and anal sphincter injury as compared to AGDac. [ Figure 2]. Specificity of AGDaf was better for ≥ 2nd degree perineal tears, while for sphincter injury, AGDac was more specific. Significant risk factors for perineal tears were left occiput anterior fetal head position and neonatal birth weight. In Pelvic Floor Distress Inventory score (PFDI-20) at 6 weeks postpartum, symptoms pertaining to pelvic organ prolapse and bowel were significantly higher in cases as compared to controls; however, urinary symptoms were comparable. Pelvic Floor Muscle strength was found to be similar in cases and controls at 6 weeks postpartum.
The Receiver Operator Curve (ROC) was plotted to obtain the cut off value of AGDac and AGDaf for predicting second degree or higher perineal tears. It was observed that at the cut-off value of 77.05mm, AGDac was 60% sensitive and 50% specific, with the positive predictive value of 54.5% and negative predictive value of 55.5% in predicting second degree or higher perineal tears.
Also, at a cut-off value of 33.75mm, AGDaf was 75% sensitive and 55% specific with positive predictive value of 62.5% and negative predictive value of 68.7% in predicting second degree or higher perineal tears.
It was observed that Area under the curve (AUC) was higher for AGDaf (0.688) as compared to AGDac (0.569), making AGDaf a more reliable parameter for predicting second degree or higher perineal tears.

In our study, shorter AGDaf (anus to fourchette distance) was found to have good sensitivity for predicting second-degree or higher perineal tears. For predicting Obstetric Anal Sphincter injury, in particular, AGDaf had better sensitivity than AGDac (anus to clitoris distance), however, its specificity was lower than the latter.

Measurement of Anogenital Distance with vernier callipers in obstetrics patients is simple, cost-effective and can be performed easily. If Anogenital Distance is found to be short along with risk factors for perineal tears, the obstetrician conducting delivery can be more cautious. This can reduce the occurrence of obstetric anal sphincter injuries and their long-term consequences.

Jain VG, Goyal V, Chowdhary V, Swarup N, Singh RJ, Singal A, et al. Anogenital distance is determined during early gestation in humans. Hum Reprod. 2018;33(9):1619-1627.
Moya-Jiménez LC, Sánchez-Ferrer ML, Adoamnei E, Mendiola J. New approach to     the evaluation of perineal measurements to predict the likelihood of the need for an episiotomy. Int Urogynecol J. 2019;30(5):815-821.
Sánchez-Ferrer ML, Moya-Jiménez LC, Mendiola J. Comparación de la distancia anogenital y antropometría del periné en pacientes con y sin prolapso de órganos pélvicos. Actas Urológicas Españolas. 2016;40:628-634.

Continence 7S1 (2023) 100899
DOI: 10.1016/j.cont.2023.100899