Related Experiment Video
Updated: May 1, 2026

Anogenital Distance and Perineal Measurements of the Pelvic Organ Prolapse POP Quantification System
Published on: September 20, 2018
Does a large infant head or a short perineal body increase the risk of obstetrical perineal trauma?
Leanne K Komorowski1, Lawrence M Leeman, Anne M Fullilove
1Southcentral Foundation, Anchorage, AK, USA.
Background:
Perineal trauma after vaginal delivery can have significant long-term consequences. It is unknown if a larger infant head circumference or smaller maternal perineal anatomy are risk factors for perineal trauma after vaginal delivery.
Methods:
We conducted a prospective cohort study of low-risk nulliparous women. Data collected included maternal characteristics, antepartum Pelvic Organ Prolapse Quantification measurements of the perineal body and genital hiatus, labor characteristics, perineal trauma, and infant head circumference. Perineal trauma was defined as trauma that extended into the muscles of the perineum (second-degree or deeper). Univariate and multivariate logistic models were created to calculate odds ratios (OR) and 95 percent confidence intervals (CI).
Results:
We observed 448 vaginal births. Multivariate analysis demonstrated a significant association between infant head circumference at birth and perineal trauma: OR 1.22 for each increase of 1 cm in head circumference (95% CI 1.05-1.43). There was no association between perineal body or genital hiatus length and perineal trauma.
Conclusions:
In nulliparous low-risk women a larger infant head circumference at birth increases the likelihood of perineal trauma, although the effect is modest. Antenatal perineal body and genital hiatus measurements do not predict perineal trauma. These results do not support alteration in mode of delivery or other obstetric practices.
Related Concept Videos
Increased Intracranial Pressure ll: Pathophysiology
Muscles of the Pelvic Floor and Perineum
Perineal Layer
The perineum is a diamond-shaped area below the pelvic diaphragm, divided into an anterior urogenital triangle that contains the external genitals and a posterior anal triangle housing the anus. The urogenital...
Increased Intracranial Pressure l: Introduction
Local Anesthetics: Clinical Application as Epidural Anesthesia
Since epidural anesthetics can be infused through an epidural catheter, all types of drugs, including short-acting ones, can be administered. Chloroprocaine and lidocaine are examples of short and long-duration anesthetics, respectively. Bupivacaine...

