Androgen-regulated cervical ripening: a structural, biomechanical, and molecular analysis

Association between fetal sex and pregnancy outcomes among women with twin pregnancies: a multicenter cross-sectional study

PURPOSE

To examine the frequency and to what extent fetal sex is associated with pregnancy outcomes among twin pregnancies, stratified by chorionicity.

METHODS

This registry-based multicenter cross-sectional study was conducted using the Japan Society of Obstetrics and Gynecology perinatal database between 2007 and 2016. The sample population was restricted to women with twin pregnancies. The main pregnancy-related outcomes included preterm birth, very preterm birth, extremely preterm birth, preeclampsia, twin-to-twin transfusion syndrome (TTTS), and selective intrauterine growth restriction (s-IUGR). Birth weight, small for gestational age (SGA), and fetal death were also investigated.

RESULTS

The primary analysis was performed based on 37,953 women, including 23,804 women with dichorionic diamniotic (DD) twins and 14,149 women with monochorionic diamniotic (MD) twins. Women with male/male DD twins had a significantly higher risk of preterm birth (adjusted risk ratio [aRR]: 1.07, 95% confidence interval [CI]: 1.03-1.10) and a lower risk of preeclampsia (aRR: 0.74, 95% CI: 0.62-0.88) than women with female/female DD twins. Women with male/male MD twins also had a significantly higher risk of preterm birth (aRR: 1.06, 95% CI: 1.04-1.09) than women with female/female MD twins. Risks of preeclampsia, TTTS, and s-IUGR did not differ by sex among MD pregnancies. Male SGA risk was significantly higher among male/male twins than among male/female DD twins. Among MD twins, risks of SGA and fetal death were significantly higher in male/male fetuses.

CONCLUSIONS

This study demonstrated significant associations between fetal sex and several pregnancy outcomes in twin pregnancies, some of which differed by chorionicity.

Practical Approach to Hyperandrogenism in Women

The approach to hyperandrogenism in women varies depending on the woman's age and severity of symptoms. Once tumorous hyperandrogenism is excluded, the most common cause is PCOS. Hirsutism is the most common presenting symptom. The woman's concern about her symptoms plays an important role in the management of disease. Although measurement of testosterone is useful in identifying an underlying cause, care must be taken when interpreting the less accurate assays that are available commercially. Surgical resection is curative in tumorous etiologies, whereas medical management is the mainstay for non-tumorous causes.

Polycystic Ovary Syndrome and the Forgotten Uterus

Polycystic ovary syndrome (PCOS) is a common disorder that affects various facets of fertility. Although the ovarian and metabolic aspects of the disease is well studied, its role in uterine dysfunction is not well understood. Our objective was to review the features of endometrial and uterine aberrations in women with PCOS. A systematic literature search was performed in PubMed, Medline, and the Cochrane Library databases for papers published in English up to March 2020. The following key words were used for the search: polycystic ovary syndrome, poly cystic ovarian disease, polycystic ovaries, PCOS, PCOD, PCO, PCOM, oligoovulation, anovulation, oligomenorrhea, amenorrhea, hyperandrogenism and this was combined with terms; endometrium, infertility, uterus, progesterone resistance, endometrial hyperplasia, pregnancy outcomes, preterm delivery. In this review, we highlight various uterine pathologies that are associated with PCOS and explore its impact on fertility. We also discuss key uterine molecular pathways that are altered in PCOS that may be related to infertility, endometrial hyperplasia and cancer.

Androgen receptor and uterine histoarchitecture in a PCOS rat model

Polycystic ovary syndrome (PCOS) is associated with hyperandrogenemia and uterine abnormalities. Our aim was to investigate the uterine effects of PCOS that are mediated through the androgen receptor (AR). After weaning, female rats were treated with sesame oil (Control), dehydroepiandrosterone (DHEA), or DHEA + flutamide (FLU, an AR antagonist) for 20 consecutive days. On postnatal day 41, serum, ovarian and uterine tissues were collected. DHEA and DHEA + FLU rats showed increased testosterone levels. DHEA rats showed increased epithelial height, glandular density, subepithelial stroma and myometrial thickness, associated with decreased nuclei density. These rats also showed increased uterine water content, with decreased aquaporin (AQP) 3, 7 and 8 expression in the uterine epithelium and increased AQP8 expression in the myometrium. DHEA rats also showed decreased uterine collagen remodeling, decreased cell proliferation in the subepithelial stroma, and increased apoptosis in the luminal and glandular epithelium and in the myometrium. They also showed an increase in insulin-like growth factor-1 and a decrease in phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase. The uterine stroma of DHEA rats showed no changes in progesterone receptor or estrogen receptor alpha (ERα) and increased AR expression. DHEA + FLU rats showed a smaller increase in the myometrial thickness, an increase in the uterine water content without AQP8 induction and a smaller decrease in collagen remodeling. These rats also showed no apoptosis induction and decreased proliferation in the myometrium, decreased ERα in the subepithelial stroma and myometrium and no modifications in AR. Our results demonstrate that the uterine cell turnover and collagen remodeling in DHEA rats are regulated through AR, directly or indirectly associated with ERα expression.

Impact of estrogens in males and androgens in females

Androgens and estrogens are known to be critical regulators of mammalian physiology and development. While these two classes of steroids share similar structures (in general, estrogens are derived from androgens via the enzyme aromatase), they subserve markedly different functions via their specific receptors. In the past, estrogens such as estradiol were thought to be most important in the regulation of female biology, while androgens such as testosterone and dihydrotestosterone were believed to primarily modulate development and physiology in males. However, the emergence of patients with deficiencies in androgen or estrogen hormone synthesis or actions, as well as the development of animal models that specifically target androgen- or estrogen-mediated signaling pathways, have revealed that estrogens and androgens regulate critical biological and pathological processes in both males and females. In fact, the concept of "male" and "female" hormones is an oversimplification of a complex developmental and biological network of steroid actions that directly impacts many organs. In this Review, we will discuss important roles of estrogens in males and androgens in females.

Up-regulation of Biglycan is Associated with Poor Prognosis and PTEN Deletion in Patients with Prostate Cancer

Biglycan (BGN), a proteoglycan of the extracellular matrix, is included in mRNA signatures for prostate cancer aggressiveness. To understand the impact of BGN on prognosis and its relationship to molecularly defined subsets, we analyzed BGN expression by immunohistochemistry on a tissue microarray containing 12,427 prostate cancers. Seventy-eight percent of 11,050 interpretable cancers showed BGN expression, which was considered as low intensity in 47.7% and as high intensity in 31.1% of cancers. BGN protein expression rose with increasing pathological tumor stage, Gleason grade, lymph node metastasis and early PSA recurrence (P<.0001 each). Comparison with our molecular database attached to the TMA revealed that BGN expression was linked to presence of TMPRRS2:ERG fusion and PTEN deletion (P<.0001 each). In addition, BGN was strongly linked to androgen-receptor (AR) levels (P<.0001), suggesting a hormone-depending regulation of BGN. BGN up-regulation is a frequent feature of prostate cancer that parallels tumor progression and may be useful to estimate tumor aggressiveness particularly if combined with other molecular markers.

Gestational Hyperandrogenism in Developmental Programming

Androgen excess (hyperandrogenism) is a common endocrine disorder affecting women of reproductive age. The potential causes of androgen excess in women include polycystic ovary syndrome, congenital adrenal hyperplasia (CAH), adrenal tumors, and racial disparity among many others. During pregnancy, luteoma, placental aromatase deficiency, and fetal CAH are additional causes of gestational hyperandrogenism. The present report reviews the various phenotypes of hyperandrogenism during pregnancy and its origin, pathophysiology, and the effect of hyperandrogenism on the fetal developmental trajectory and offspring consequences.

Use of nonhuman primates for the development of bioengineered female reproductive organs

Nonhuman primates (NHPs) have been widely used in reproductive biology, neuroscience, and drug development since a number of primate species are phylogenetically close to humans. In this review, we summarize the use of NHPs for nonclinical application in the reproductive system disorders including the loss or failure of an organ or tissue. Causes of infertility include congenital aplasia and acquired disorders of the reproductive organs. In addition, anti-cancer treatments can deplete ovarian follicles, leading to premature ovarian failure, infertility and long-term health risks. Along with a limited supply of human reproductive organs, anatomic/physiologic similarities to humans support the need for NHP models (New-World monkeys such as the common marmoset and Old-World monkeys such as cynomolgus and rhesus monkeys) to promote the advances in female infertility studies. For maintaining and executing animal studies using NHP, special protocols including animal care, anesthetic protocol, surgical technique, and immunosuppressive protocol are necessary. With a growing interest in the potential therapies such as endometrial tissue engineering, and ovary/follicle cryopreservation and grafting in Korea, this review can be useful in selecting appropriate animal models and can bridge between nonclinical studies and clinical applications by providing detailed information on the use of NHPs in the field of reproductive organ disorders.

Cervical Length and Androgens in Pregnant Women With Polycystic Ovary Syndrome: Has Metformin Any Effect?

CONTEXT

Women with polycystic ovary syndrome (PCOS) have increased risk of preterm delivery. Shortening of the cervix is a sign of preterm delivery.

OBJECTIVE

This study aimed to investigate potential effect of metformin on cervical length and whether androgen levels correlate with cervical length in PCOS pregnancies.

DESIGN AND SETTING

This was a sub-study of a randomized, placebo-controlled, multicenter study (The PregMet study) performed at 11 secondary or tertiary centers from 2005 to 2009.

PARTICIPANTS

Two-hundred sixty-one pregnancies of 245 women with PCOS, age 18-42 years participated.

INTERVENTIONS

Participants were randomly assigned to metformin or placebo from first trimester to delivery.

OUTCOME MEASUREMENTS

We compared cervical length and androgen levels in metformin and placebo groups at gestational weeks 19 and 32. We also explored whether cervical length correlated with androgen levels.

RESULTS

We found no difference in cervical length between the metformin and the placebo groups at gestational week 19 and 32. Dehydroepiandrosterone (DHEAS) tended to be higher in the metformin group. There were no correlations between androgens and cervical length at week 19. At gestational week 32, androstenedione (P = .02) and DHEAS (P = .03) showed a trend toward negative correlation to cervical length. High androstenedione level correlated with shortening of cervical length from week 19 to 32 when adjusted for confounders (P = .003). T (P = .03), DHEAS (P = .02), and free testosterone index (P = .03) showed a similar trend.

CONCLUSION

Metformin in pregnancy did not affect cervical length in women with PCOS. High maternal androgen levels correlated with cervical shortening from the second to the third trimester of pregnancy, as a sign of cervical ripening.

Material properties of mouse cervical tissue in normal gestation

An appropriately timed cervical remodeling process is critical for a healthy delivery, yet little is known about the material property changes of the cervix in pregnancy because obtaining human tissue samples is difficult. Rodent models offer advantages including accurately timed pregnant tissues and genetically altered models. Determining the material properties of the mouse cervix, however, is challenging because of its small size and complex geometry. The aim of this study is to quantify cervical material property changes in a normal mouse pregnancy using a microstructurally-inspired porous fiber composite model. We mechanically test intact, whole, gestation-timed mouse cervix by pulling apart tensioned sutures through its inner canal. To interpret our mechanical testing results, we conduct an inverse finite element analysis, taking into account the combined loading state of the thick-walled cylindrical tissue. We fit the material model to previous osmotic swelling data and load-deformation data from this study using a nonlinear optimization scheme, and validate the model by predicting a separate set of deformation data. Overall, the proposed porous fiber composite model captures the mechanical behavior of the mouse cervix in large deformation. The evolution of cervical material parameters indicates that in a normal mouse pregnancy, the cervix begins to soften between day 6 and day 12 of a 19-day gestation period. The material parameter associated with the collagen fiber stiffness decreases from 3.4MPa at gestation day 6 to 9.7e-4MPa at gestation day 18, while the ground substance stiffness decreases from 2.6e-1MPa to 7.0e-4MPa.

STATEMENT OF SIGNIFICANCE

Accelerated cervical remodeling can lead to extremely premature births. Little is known, however, about the material property changes of the cervix in pregnancy because pregnant human tissue samples are limited. Rodent models overcome this limitation and provide access to gestation-timed samples. Measuring the material property changes of the mouse cervix in pregnancy is challenging due to its small size and complex geometry. Here, we establish a combined experimental and modeling framework. We use this framework to determine the cervical material property changes throughout a normal mouse pregnancy. We present our experimental methods for mechanically testing whole, intact cervical tissue samples. We fit a porous fiber composite material model to the mechanical data and show that the mouse cervix begins to soften between day 6 and day 12 of a 19-day gestation period.

Androgens in pregnancy: roles in parturition

BACKGROUND

Understanding the physiology of pregnancy enables effective management of pregnancy complications that could otherwise be life threatening for both mother and fetus. A functional uterus (i) retains the fetus in utero during pregnancy without initiating stretch-induced contractions and (ii) is able to dilate the cervix and contract the myometrium at term to deliver the fetus. The onset of labour is associated with successful cervical remodelling and contraction of myometrium, arising from concomitant activation of uterine immune and endocrine systems. A large body of evidence suggests that actions of local steroid hormones may drive changes occurring in the uterine microenvironment at term. Although there have been a number of studies considering the potential role(s) played by progesterone and estrogen at the time of parturition, the bio-availability and effects of androgens during pregnancy have received less scrutiny. The aim of this review is to highlight potential roles of androgens in the biology of pregnancy and parturition.

METHODS

A review of published literature was performed to address (i) androgen concentrations, including biosynthesis and clearance, in maternal and fetal compartments throughout gestation, (ii) associations of androgen concentrations with adverse pregnancy outcomes, (iii) the role of androgens in the physiology of cervical remodelling and finally (iv) the role of androgens in the physiology of myometrial function including any impact on contractility.

RESULTS

Some, but not all, androgens increase throughout gestation in maternal circulation. The effects of this increase are not fully understood; however, evidence suggests that increased androgens might regulate key processes during pregnancy and parturition. For example, androgens are believed to be critical for cervical remodelling at term, in particular cervical ripening, via regulation of cervical collagen fibril organization. Additionally, a number of studies highlight potential roles for androgens in myometrial relaxation via non-genomic, AR-independent pathways critical for the pregnancy reaching term. Understanding of the molecular events leading to myometrial relaxation is an important step towards development of novel targeted tocolytic drugs.

CONCLUSIONS

The increase in androgen levels throughout gestation is likely to be important for establishment and maintenance of pregnancy and initiation of parturition. Further investigation of the underlying mechanisms of androgen action on cervical remodelling and myometrial contractility is needed. The insights gained may facilitate the development of new therapeutic approaches to manage pregnancy complications such as preterm birth.

Inhibitory effect of progesterone on cervical tissue formation in a three-dimensional culture system with human cervical fibroblasts

Progesterone supplementation is recommended to prevent preterm birth in women with a short cervix, but the mechanism is unclear. We hypothesize that progesterone acts by altering the composition of the cervical extracellular matrix (ECM). We tested this hypothesis using human cervical fibroblasts in both two-dimensional (2D) and three-dimensional (3D) cultures. For 2D culture, cells were seeded in 6-well plates and cultured with media supplemented with estradiol (10(-8) M), progesterone (10(-7) or 10(-6) M), and vehicle. For 3D culture, the cells were cultured on a porous silk protein scaffold system. Progesterone and estrogen receptors were documented by immunohistochemistry and Western blot analysis. In both 2D and 3D cultures, decreased collagen synthesis was seen with increased progesterone concentration. Three-dimensional cultures could be maintained significantly longer than 2D cultures, and the morphology of 3D cultures appeared similar to native cervical tissue. Thus, further studies were performed in 3D culture. To determine the effect of progesterone concentration, the 3D scaffolds were cultured with estradiol (10(-8) M) and five conditions: vehicle; 10(-9), 10(-8), or 10(-7) M progesterone; or 10(-7) M progesterone plus 10(-6) M mifepristone. The highest progesterone concentration correlated with the least amount of collagen synthesis. Collagen synthesis progressively increased as progesterone concentration decreased. This effect was partially antagonized by mifepristone, suggesting the mechanism is mediated by the progesterone receptor. This hormonally responsive 3D culture system supports the hypothesis that progesterone has a direct effect on remodeling cervical ECM during pregnancy. The 3D culture system could be useful for studying the mechanism of progesterone effects on the cervix.

System-level biomechanical approach for the evaluation of term and preterm pregnancy maintenance

Preterm birth is the primary contributor to perinatal morbidity and mortality, with those born prior to 32 weeks disproportionately contributing compared to those born at 32-37 weeks. Outcomes for babies born prematurely can be devastating. Parturition is recognized as a mechanical process that involves the two processes that are required to initiate labor: rhythmic myometrial contractions and cervical remodeling with subsequent dilation. Studies of parturition tend to separate these two processes rather than evaluate them as a unified system. The mechanical property characterization of the cervix has been primarily performed on isolated cervical tissue, with an implied understanding of the contribution from the uterine corpus. Few studies have evaluated the function of the uterine corpus in the absence of myometrial contractions or in relationship to retaining the fetus. Therefore, the cervical-uterine interaction has largely been neglected in the literature. We suggest that a system-level biomechanical approach is needed to understand pregnancy maintenance. To that end, this paper has two main goals. One goal is to highlight the gaps in current knowledge that need to be addressed in order to develop any comprehensive and clinically relevant models of the system. The second goal is to illustrate the utility of finite element models in understanding pregnancy maintenance of the cervical-uterine system. The paper targets an audience that includes the reproductive biologist/clinician and the engineer/physical scientist interested in biomechanics and the system level behavior of tissues.

A novel optical method to assess cervical changes during pregnancy and use to evaluate the effects of progestins on term and preterm labor

OBJECTIVE

The purpose of this study was to determine whether optical methods can estimate cervix function during pregnancy and whether progestins modify this process.

STUDY DESIGN

Photos of the external cervix of timed-pregnant rats were taken every other day from day 13 until postpartum day 5 after daily treatments with vehicle (controls) or progestin treatments (progesterone, subcutaneously or vaginally; 17-alpha-hydroxyprogesterone caproate [17P] and RU-486 subcutaneously, once on day 16). The surface area of the cervix was estimated from photos.

RESULTS

The surface area of cervix increases throughout pregnancy and reverses after delivery in controls. In the progesterone subcutaneously or 17P subcutaneously groups, increases in surface area are lower (17P group until day 19 only; P < .05). Vaginal progesterone does not prevent surface area increases. Only the progesterone subcutaneously blocked delivery. RU-486 increases the surface area of the cervix (P < .05) during preterm delivery.

CONCLUSION

An optical method is useful for quantitative assessment of the cervix and evaluation of agents that modify cervical function.

Cervical tissue engineering using silk scaffolds and human cervical cells

Spontaneous preterm birth is a frequent complication of pregnancy and a common cause of morbidity in childhood. Obstetricians suspect abnormalities of the cervix are implicated in a significant number of preterm births. The cervix is composed of fibrous connective tissue and undergoes significant remodeling in preparation for birth. We hypothesized that a tissue engineering strategy could be used to develop three-dimensional cervical-like tissue constructs that would be suitable for investigating cervical remodeling. Cervical cells were isolated from two premenopausal women undergoing hysterectomy for a benign gynecological condition, and the cells were seeded on porous silk scaffolds in the presence or absence of dynamic culture and with 10% or 20% serum. Morphological, biochemical, and mechanical properties were measured during the 8-week culture period. Cervical cells proliferated in three-dimensions and synthesized an extracellular matrix with biochemical constituents and morphology similar to native tissue. Compared to static culture, dynamic culture was associated with significantly increased collagen deposition (p < 0.05), sulfated glycosaminoglycan synthesis (p < 0.05), and mechanical stiffness (p < 0.05). Serum concentration did not affect measured variables. Relevant human tissue-engineered cervical-like constructs constitute a novel model system for a range of fundamental and applied studies related to cervical remodeling.

Pharmacologic actions of progestins to inhibit cervical ripening and prevent delivery depend on their properties, the route of administration, and the vehicle

OBJECTIVE

The purpose of this study was to evaluate cervical changes and delivery at term during pregnancy in rats after various progestin treatments.

STUDY DESIGN

Pregnant rats were treated by various routes and vehicles with progesterone, 17-alpha-hydroxyprogesterone caproate (17P), R5020, and RU-486. Delivery time was determined and cervical ripening was assessed in vivo by collagen light-induced fluorescence.

RESULTS

The cervix is rigid in the progesterone injection, 17P, and vaginal R5020 groups vs controls. Vaginal progesterone had no effect. RU-486 treatment softened the cervix during preterm delivery. Only subcutaneous injected progesterone, R5020 (subcutaneous and vaginal), and topical progesterone in sesame and fish oil inhibits delivery. Delivery is not changed by subcutaneous injection of 17P, vaginal progesterone, oral progesterone, and topical progesterone in Replens (Crinone; Columbia Labs, Livingston, NJ).

CONCLUSION

Inhibition of cervical ripening and delivery by progestins depends on many factors that include their properties, the route of administration, and the vehicle. This study suggests reasons that the present treatments for preterm labor are not efficacious.

Prostaglandin treatment is associated with a withdrawal of progesterone and androgen at the receptor level in the uterine cervix

Treatment with prostaglandin(PG)-E2 is clinically efficient for cervical priming. The aim of this study was to evaluate the impact of PG-E2 on the expression of the progesterone (PR), androgen (AR) and glucocorticoid (GR) receptors in human uterine cervix in prolonged pregnancy. The study groups were postterm nulliparous women with unripe cervices undergoing cervical priming with PG-E2 before labor induction. Responders (n = 12) who delivered vaginally were compared with non-responders (n = 10), who underwent cesarean section due to failure to progress to the active phase of labor. Controls (n = 18) with vaginal partus at a normal gestational age served as a reference group. Cervical levels of PR-A and PR- B isoforms, AR and GR, serum levels of their ligands and sex hormone-binding globulin (SHBG) were quantified. The responder group displayed lower total PR-AB and AR protein levels as compared to non-responders, and lower PR-B and AR protein levels as compared to controls. In addition, the PR mRNA level was lower in responders as compared to non-responders. The GR protein level did not differ between the groups. We conclude that successful PG-E2 priming was followed by a progesterone and androgen withdrawal at the receptor level in the uterine cervix.

The contribution of maternal race/ethnicity and fetal sex to prematurity in twins

OBJECTIVE

The contribution of male fetal sex to twin preterm birth (PTB) rates was evaluated in the United States.

STUDY DESIGN

The 2002 National Center for Health Statistics Natality database was analyzed for fetal sex and twin gestations based on birth sex for MM and FF pairs (M, male; F, female). Multivariable Cox proportional hazards regression was applied to estimate the hazard ratio for PTB with adjustments for known risks.

RESULTS

Thirty-three thousand nine hundred twenty-six pairs were analyzed. PTBs between 20-36 completed weeks occurred in 59.1% MM pairs and 57.5% FF pairs. MM sex was an independent risk factor for PTB. This effect was greatest for deliveries between 20-29 weeks (hazard ratio, 1.224; 95% CI, 1.113-1.346). The effect was most pronounced in non-Hispanic white MM pairs.

CONCLUSION

In the United States, MM pairs are at greater risk for PTB. Race and ethnicity modulate sex effects. Further studies are needed to understand potential mechanisms.

Genetic background affects the biomechanical behavior of the postpartum mouse cervix

OBJECTIVE

We hypothesized that the genetic makeup has an impact on the functional behavior of the uterine cervix. Therefore, we compared the biomechanical properties of uterine cervix in postpartum in 2 strains of mice that differ in their underlying regenerative collagen remodeling characteristics: MRL/MpJ+/+ (MRL: high regenerative repair) and C57BL/6 (C57: low regenerative high fibrotic repair).

STUDY DESIGN

Cervical tensile proprieties were assessed on day 3, 15, and 60 postpartum in MRL (n = 14) and C57 (n = 13) mice (4-5 animals at each time point). Stress-strain curves were generated using Shimadzu EZ-test instrumentation. Cervical tissue was stretched by 0.42 mm/min until rupture. Parameters of viscoelasticity including slope (a measure of stiffness), yield point (YP; moment when tissue changes its proprieties from elastic to plastic), and break point (BP; measure of tissue strength) were recorded and analyzed blindly between strains. Data were normalized to the weight of the tissue and analyzed by 2-way analysis of variance. Histological and collagen birefringence evaluation of the uterine cervix (MRL: n = 4; C57: n = 4) was performed 5 days after delivery.

RESULTS

At 3 and 15 days postpartum, cervices of MRL mice were significantly more compliant than those of C57 (P < .001). MRL mice displayed a significant increase in stiffness from day 3 to day 60 (slope, median +/- SEM: day 3: 3.1 +/- 0.5 vs day 15: 20.3 +/- 4.9 vs day 60: 33.1 +/- 3.5 N/mm per gram; P < .001). In contrast, the stiffness of C57 cervices reached maximum on day 15 (slope day 3: 14.1 +/- 4.3 vs day 15: 40.0 +/- 6.5 N/mm per gram; P = .02) and rested at a similar level on day 60 (day 60: 26.1 +/- 7.0 N/mm per gram; day 60 vs day 15: P = .937). More force was required to reach YP in C57 on day 3 (C57: 72.5 +/- 14.7 vs MRL: 19.9 +/- 1.6 N/g; P < .001) but not on either day 15 (C57: 156.1 +/- 27.5 vs MRL: 109.2 +/- 26.0 N/g; P = .120) or on day 60 (C57: 143.4 +/- 26.5 vs MRL: 164.5 +/- 18.7 N/g; P = .412). There was a significant decrease in BP in both strains on both day 15 and day 60 compared with day 3 postpartum (P = .856 for strain, P = .008 for day). MRL mice displayed significantly less cervical collagen birefringence compared with C57 control (P < .001) but increased proteoglycan staining and increased water content.

CONCLUSION

We provide evidence that genetic makeup may have an impact on cervical tissue remodeling and function. There are significant differences in postpartum cervical stiffness and compliance that vary with the regenerative collagen remodeling phenotype.