WELCOME!
Each issue cuts through the noise and delivers concise, evidence-based insights you can apply in practice right away straight to your inbox. This first issue focuses on the genital hiatus—an often-overlooked yet clinically significant structure of the pelvic floor. We’ll discuss the factors that affect its size, the changes that it goes through during pregnancy and postpartum, and what the latest research tells us about improving hiatal closure and surgical outcomes. And, of course, we’ll talk about some clinical takeaways that you can apply to your next patient.
Let’s dive in.
Understanding Hiatus Changes: Clinical Insights from Recent Research
Cheng et al. (2023) examined 540 different studies on levator hiatus (LH) and urogenital hiatus (UGH) changes following delivery and provides valuable insights for clinical practice. This research tells us a number of things:
Factors affecting hiatal size, hiatal closure, and its implications in stress urinary incontinence (SUI) and pelvic organ prolapse (POP) treatment.
The story of the hiatal changes through delivery and postpartum.
Image: UGH and LH diagram

UGH - purple circle
LH - yellow oval
WHAT AFFECTS HIATAL SIZE?
Factors (such as age, ethnicity, and body weight/BMI) can influence the hiatal dimensions.
Age plays a role in hiatal shape. Older patients typically present with U-shaped UGH on MRI, while younger individuals more commonly have V-shaped patterns. With ultrasound, the LH was more oval in older patients and more circular in younger patients. MRIs of nulliparous women demonstrated that women over 70 years of age had a 30% larger UGH at rest and a 11% larger UGH during a valsalva maneuver when compared to nulliparous women under the age of 40.
Ethnicity also influences hiatal measurements due to variations in bony pelvis structure and pelvic anatomy. The authors looked at a few studies of nulliparous women and learned black women had a larger LH followed by Caucasian women and, lastly, South Asian Women. In the same study, there was no difference between the ethnicities and UGH. Another study found nulliparous pregnant Asian women had greater pelvic floor thickness (14%) and area (18%) when compared to nulliparous pregnant Caucasian women.
Body weight correlates with larger AP hiatal diameter and overall area, however BMI specifically affects only the AP diameter.
PREGNANCY, DELIVERY, AND HIATAL CHANGES
The mechanism behind hiatal enlargement during pregnancy isn't completely understood, but likely involves muscle changes, increased connective tissue compliance, and elevated intra-abdominal pressure.
The LH enlarges first during the second stage of labor, followed by the UGH. In the delivery process, the UGH can stretch up to 255%.
If the hiatus fails to close after delivery, SUI or POP can develop. Several factors impact hiatal closure following delivery. These include:
Levator ani muscle condition
Resting muscle tone
Contraction strength
Perineal body integrity
We can assess all of these through manual examination.
If a pregnant woman struggles with smaller hiatal dimensions during labor, she faces a higher likelihood of instrument-assisted delivery which could lead to a levator avulsion. Levator avulsion rates vary significantly by delivery type:
15% with spontaneous vaginal delivery
21% with vacuum-assisted delivery
52% with forceps-assisted delivery
Both vacuum and forceps deliveries result in larger hiatal measurements postpartum compared to spontaneous delivery.
Immediately post-delivery, hiatal measurements increase during both Valsalva maneuvers and Kegel. Recovery follows a predictable timeline - the fastest reduction occurs within the first two weeks, while the most substantial improvements happen during the first 4-6 months postpartum. The current evidence does not show hiatal measurements returning to nulliparous state.
LEVATOR INJURIES
Women with levator injuries demonstrate persistently larger hiatal dimensions in both short-term and long-term follow-up. Forceps delivery carries the highest risk for levator avulsion, and studies show concerning correlations between mid-pelvic forceps delivery rates and pelvic organ prolapse surgery rates 10 years later.
Interestingly, women with unilateral levator defects demonstrate significantly greater hiatal area improvement (18%) than those with bilateral defects (9%), suggesting that some compensation mechanisms remain intact.
Cesarean delivery generally results in a smaller hiatal area compared to vaginal delivery. At 4-6 months postpartum, patients who underwent cesarean delivery exhibited hiatal measurements similar to first trimester values, with significantly smaller areas during Valsalva (9% reduction) and Kegel exercises (6% reduction). However, levator avulsion can occur even with cesarean delivery, particularly when surgery occurs during a prolonged second stage of labor.
HIATUS SIZE AND PELVIC FLOOR (DYS)FUNCTION
Pelvic floor muscle strength represents one of several factors that affects both the UGH and the LH sizes. Research shows moderate correlations between hiatal size and various strength parameters including resting pressure, pelvic floor muscle strength, and muscle endurance.
Dysfunction patterns show clear relationships with hiatal size:
Women with SUI have 15% larger hiatal dimensions during both rest and Kegel.
Women with POP show 32% larger measurements under the same conditions
Encouragingly, intensive pelvic muscle training over 6 months produces measurable improvements: 6% reduction in LH area at rest, 8% improvement during Valsalva, 36% better shortening of the LH AP diameter during contraction, and 30% increase in vaginal squeeze pressure.
SURGICAL CONSIDERATIONS
Larger hiatal dimensions correlate with increased surgical failure rates. Recent studies examining hiatal changes before and after surgery reveal important prognostic information, such as:
Four to 6 weeks after sacrocolpopexy, patients with a persistently enlarged urogenital hiatus experienced higher failure rates (14.0%) compared to those with improved measurements (5.7%) or stable normal dimensions (4%).
Patients receiving a posterior colporrhaphy with a sacropexy experienced larger decreases in UGH size than those who did not have a posterior colporrhaphy.
However, patients undergoing apical suspension (regardless of concomitant posterior colporrhaphy) had reduced UGH when measured during valsalva postoperatively.
Placement of a puborectalis sling after prolapse repair completion reduced the LH area by 30% on Valsalva at 2 months after surgery - and those improvements were sustained at 2 years!
CLINICAL APPLICATIONS
During examination, pay attention to:
LH and UGH size
Pelvic floor contraction strength (this is moderately correlated with hiatal sizes -weaker muscles often accompany larger hiatal openings)
Resting pelvic floor muscle tone (lower resting tone correlates with a larger hiatal area)
The perineal body (Is there a prior history of significant tearing or episiotomy? If there is a scar, does it move?)
Observable Patterns
Parous women with prolapse often demonstrate increased hiatus size at rest and during Valsalva maneuvers.
Prolapse size correlates with the size of the hiatus in parous women only. Women with grade III or IV prolapse had 32% and 71% larger UGH than women with a grade II prolapse.
An enlarged genital hiatus will look like it’s ballooning during a Valsalva maneuver.
KEY TAKEAWAYS
The LH and UGH serve as important clinical parameters for evaluating pelvic floor function in patients. Enlarged hiatal dimensions correlate with POP and, to some extent, SUI.
Multiple factors explain less than half the variation in hiatal size, indicating that age, ethnicity, BMI, genetics, and other unmeasured factors contribute to individual differences.
It’s important to remember that pregnancy-related hiatal enlargement likely represents physiological preparation for delivery. Once postpartum, LH and UGH sizes improve quickly in the first two weeks and then continue for 4-6 months after delivery. Problems at the perineal body, low resting pelvic floor muscle tone, decreased pelvic floor strength, and levator ani integrity can cause postpartum persistence of an enlarged hiatus
Cheng, W., English, E., Horner, W., Swenson, C. W., Chen, L., Pipitone, F., Ashton-Miller, J. A., & DeLancey, J. O. L. (2023). Hiatal failure: effects of pregnancy, delivery, and pelvic floor disorders on level III factors. International urogynecology journal, 34(2), 327–343. https://doi.org/10.1007/s00192-022-05354-8
ADDITIONAL RESEARCH TAKE AWAYS…
Lakovschek, I. C., Trutnovsky, G., Obermayer-Pietsch, B., & Gold, D. (2022). Longitudinal Study of Pelvic Floor Characteristics Before, During, and After Pregnancy in Nulliparous Women. Journal of ultrasound in medicine : Official journal of the American Institute of Ultrasound in Medicine, 41(1), 147–155. https://doi.org/10.1002/jum.15689
A first of its kind study looking at pelvic floor changes from pre-pregnancy to postpartum. Prior to this study, only a few studies looked at the pelvic floor in the first trimester.
What you need to know: Low recruitment and subject attrition resulted in an underpowered study, so no statistical conclusions could be drawn. Despite these results, the study starts to explain the changes that occur from pre-conception to postpartum.
Decreased bladder neck mobility and a lowered bladder neck, cervix, and anorectal junction positions were the changes from pre-conception to the end of first trimester.
Increased bladder neck mobility, lower positioning of the bladder neck and anorectal junction when comparing measurements from postpartum to pre-conception.
Cason, S. N., Moalli, P. A., Lockhart, M. E., Richter, H. E., Abramowitch, S. D., & Bowen, S. T. (2025). Racial differences in the levator ani muscle and levator hiatus in individuals of reproductive age. American journal of obstetrics and gynecology, 233(1), 49.e1–49.e20. https://doi.org/10.1016/j.ajog.2024.12.024
The American Journal of Obstetrics and Gynecology published examining the racial differences between the LH and levator ani muscle (LAM) thickness of Black and White women identifying individuals of reproductive age with no history of pelvic floor dysfunction. Researchers at University of Pittsburg and University of Alabama, Birmingham examined 112 pelvis MRIs of patients to assess LAM thickness and LH morphology.
What they discovered:
After controlling for parity, BMI, and age ,individuals in the Black cohort were more likely to exhibit larger LH dimensions (area, AP diameter, transverse diameter, and perimeter) and have a “U”- shaped or ovular LH. These are known risk factors for PFD, decreased muscle tone, and muscle strength.
Higher parity correlated with larger LH dimensions in White individuals, but Black individuals had no correlation.
There was no difference between Black or White individuals in LAM thickness, with exception of the “right middle” LAM being thinner in White individuals
Cheng et al (2023) reports ethnicity as a factor that affects hiatal dimensions. They discuss LAM thickness in Asian individuals but not Black individuals. The description of the levator hiatus in older individuals (50+) in the Cheng et al.(2023) study sounds similar to the dimensions of the Black individuals of this study.
PLAN
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