Maternal Age and Contractility of Human Myometrium in Pregnancy

Uterine Aging and Reproduction: Dealing with a Puzzle Biologic Topic

Uterine aging is the process of the senescence of uterine tissue, observed in all middle-aged mammals. Since the aging-related changes in the uterus are associated with infertility and poor pregnancy outcomes, with a lack of studies discussing uterine aging, authors reviewed uterine aging and its consequences on reproduction. MEDLINE, Scopus, and PubMed searches during the years 1990-2023 were performed using a combination of keywords and terms on such topics. According to the author's evaluation, articles were identified, selected, and included in this narrative review. The aging process has an unfavorable impact on the uterus of mammals. There are different and selected molecular pathways related to uterine aging in humans and animals. Uterine aging impairs the function of the uterine myometrium, neurofibers of the human uterus, and human endometrium. These biological pathways modulate oxidative stress, anti-inflammatory response, inflammation, mitochondrial function, DNA damage repair, etc. All these dysregulations have a role in poorer reproductive performance and pregnancy outcomes in older mammals. The most recent data suggest that uterine aging is accompanied by genetic, epigenetic, metabolic, and immunological changes. Uterine aging has a negative impact on the reproductive performance in mammalian species, but it could be potentially modulated by pharmacological agents, such as quercetin and dasatinib.

Unveiling uterine aging: Much more to learn

Uterine aging is an important factor that impacts fertility, reproductive health, and uterus-related diseases; however, it remains poorly explored. Functionally, these disturbances have been associated with an abnormal hormonal response in the endometrium and decreased endometrial receptivity. Based on emerging evidence, these alterations are mediated via the senescence of endometrial stem cells and impaired decidualization of endometrial stromal cells. Multiple molecular activities may participate in uterine aging, including oxidative stress, inflammation, fibrosis, DNA damage response, and cellular senescence. Over the past decade, several protective strategies targeting these biological processes have afforded promising results, including stem cell therapy, anti-aging drugs, and herbal medicines. However, the currently available evidence is fragmented and scattered. Here, we summarize the most recent findings regarding uterine aging, including functional and structural alterations and potential cellular and molecular mechanisms, and discuss potential protective interventions against uterine aging. Thereby, we hope to provide a comprehensive understanding of the pathophysiological processes and underlying mechanisms associated with uterine aging, as well as improve fecundity and reproductive outcomes in females of advanced reproductive age.

Advancing understanding of maternal age: correlating epigenetic clocks in blood and myometrium

Background:

Advanced maternal age is currently a term defined by chronological age. However, a group of biomarkers known as epigenetic clocks, which can predict morbidity and mortality, has been used to estimate measures of biological aging. Uterine myometrial function during the process of parturition may be influenced by aging, as labor dystocia, unplanned intrapartum cesarean birth, and postpartum hemorrhage are more common in older individuals. The purpose of this study was to evaluate the use of epigenetic clocks in maternal myometrium and blood for predicting age and to evaluate the correlation of epigenetic age between the tissues.

Results:

We compared epigenetic age in blood and myometrial samples provided by women undergoing planned cesarean birth at term gestation. Chronological age ranged from 20 to 50 with a median (IQR) age of 35.5(8) years. The MethylationEPIC BeadChip was used to obtain DNA methylation data, and then epigenetic age was calculated using the Horvath, Hannum, GrimAge, and PhenoAge clocks. Spearman correlations of epigenetic age with chronological age were calculated. We tested the relationship of epigenetic age in maternal blood to epigenetic age in myometrium. Age acceleration, for each clock, was also correlated between tissues. Twenty-seven participants provided samples, and 21 matched specimens were included in the final analysis after quality control. Spearman correlation between maternal chronological age and epigenetic age were significant in three of the four clocks (pan-tissue Horvath, Hannum, and GrimAge), for both myometrium and blood samples. Correlations between blood epigenetic age and maternal age ranged from 0.72 to 0.87 (all p < 0.001). Correlations between myometrial epigenetic age and maternal age were also significant (0.62–0.70, p = 0.002), though lower than correlations seen in blood. Maternal blood epigenetic age also correlated with epigenetic age in myometrium with each of these three clocks 0.60 (p = 0.004, Horvath), 0.63 (p = 0.003, Hannum), and 0.80 (p < 0.001, GrimAge). GrimAge age acceleration had the highest correlation between tissues among the clocks (0.49, p = 0.02).

Conclusions:

Given the limited sample, this study provides insight into the potential use of epigenetic age derived from blood as a proxy for myometrial epigenetic age, which may be a useful biomarker in estimating myometrial biological age in relationship to myometrial dysfunction. GrimAge outperformed the other tested clocks in terms of concordance of epigenetic age and age acceleration between tissues; however, the Horvath and Hannum clocks may be useful depending on the outcome of interest in pregnancy.

Forces Involved with Labor and Delivery-A Biomechanical Perspective

Childbirth is a primarily biomechanical process of physiology, and one that engineers have recently begun to address in a broader fashion. Computational models are being developed to address the biomechanical effects of parturition on both maternal and fetal tissues. Experimental research is being conducted to understand how maternal tissues adapt to intrauterine forces near the onset of labor. All of this research requires an understanding of the forces that are developed through maternal efforts-both uterine contractions and semi-voluntary pushing-and that can be applied by the clinician to assist with the delivery. This work reviews the current state of knowledge regarding forces of labor and delivery, with a focus on macro-level biomechanics.

Spontaneous Human Myometrial Contractility in the Third Trimester of Pregnancy in Relation to Past Mode of Delivery

OBJECTIVE

It is well established that women with a previous vaginal delivery have higher success rates in relation to vaginal birth after cesarean than those without. The aim of this study was to examine the effect of past mode of delivery on contractile parameters of human myometrium in vitro.

STUDY DESIGN

Myometrial strips were excised from 64 women at cesarean delivery (CD) and recordings of spontaneous contractile activity analyzed and compared across three clinical groups: (1) women with no previous delivery (Group 1); (2) women with CD only (Group 2); and (3) women with a history of vaginal delivery and CD (Group 3).

RESULTS

Myometrial samples from women in Group 3, women who had a previous vaginal delivery, had a significantly greater maximum amplitude of contractions (p < 0.05), a greater force (mean contractile force) of contractions (p < 0.01), and a faster rate of rise (p < 0.01) and relaxation of contractions (p < 0.05) than those in Groups 1 and 2.

CONCLUSION

Many of the functional parameters of human uterine contractions are altered, or enhanced, in the women who have had a previous vaginal delivery, when compared with those without. This may partly explain the clinical differences observed in labor.

Advanced maternal age and adverse pregnancy outcomes

A wide range of adverse pregnancy outcomes are associated with women of advanced maternal age (AMA). These include increased risks for miscarriage, chromosomal abnormalities, stillbirth, foetal growth restriction, preterm birth, pre-eclampsia, gestational diabetes mellitus and caesarean section. While a wide body of literature has reported on these risks, varying definitions in both AMA and reported outcomes can make synthesizing the information difficult when counselling an individual women about her specific risks. In this chapter, we discuss the role of AMA on adverse pregnancy outcomes with a view to clarifying the magnitude of the risks for each outcome in the context to enable more informed clinical counselling and decision-making.

Effects of maternal parity on response of human myometrium to oxytocin and ergometrine in vitro

OBJECTIVE

The aim of this study was to compare the effects of oxytocin and ergometrine on the intrinsic contractile parameters of human uterine smooth muscle at term between primiparous and multiparous women.

STUDY DESIGN

Myometrial biopsies were obtained from women undergoing planned caesarean section at term. The biopsies were dissected into eight uniform strips and mounted in tissue baths for isometric recording. The strips were challenged with increasing concentrations of oxytocin and ergometrine. Parameters of contractile activity, including mean contractile force (MCF) and maximum amplitude of contractions (MAMP) were recorded and analysed. Results were compared between primiparous (Group 1) and multiparous (Group 2) women.

RESULTS

Myometrial biopsies were obtained from n = 11 donors (88 tissue strips), of which n = 5 were Group 1 and n = 6 were Group 2. In relation to oxytocin, the MAMP value observed was significantly greater in Group 2 than in Group 1 (151 ± 18mN vs 67 ± 14mN, P < 0.01). Regarding ergometrine, the MCF response was greater in Group 2 samples (24 ± 10 mN) than that in Group 1 (18 ± 2mN) (P < 0.05).

CONCLUSION

Our findings highlight that women in a first pregnancy have a decreased response to both oxytocin and ergometrine in an in vitro setting when compared with women in a subsequent pregnancy, and this may have clinical implications regarding the management of postpartum haemorrhage in this cohort.

Delivery outcome after trial of labor in nulliparous women 40 years or older-A nationwide population-based study

INTRODUCTION

The number of women postponing childbirth until an advanced age is increasing. Our aim was to study the outcome of labor in nulliparous women ≥40 years, compared with women 25-29 years, after both spontaneous onset and induction of labor.

MATERIAL AND METHODS

The nationwide population-based Swedish Medical Birth Register was used to study the perinatal outcome in nulliparous women with a singleton, term (gestational weeks 37-44), live fetus in cephalic presentation and a planned vaginal delivery from 1992 to 2011. We included 7796 nulliparous women ≥40 years and 264 262 nulliparous women 25-29 years. Prevalence and risk of intrapartum cesarean section, operative vaginal delivery, obstetric anal sphincter injury and a 5-minute Apgar score <7 were calculated for women ≥40 years stratified for spontaneous onset and induction of labor, using women 25-29 years as the reference in both strata. Crude and adjusted odds ratios (aOR) were calculated by unconditional logistic regression and presented with 95% confidence intervals (CI).

RESULTS

Overall, 79% of women ≥40 years with a trial of labor reached a vaginal delivery. After spontaneous onset, intrapartum cesarean section was performed in 15.4% of women ≥40 years compared with 5.4% of women 25-29 years (aOR 3.07, 95% CI 2.81-3.35). Operative vaginal delivery was performed in 22.3% of women ≥40 years compared with 14.2% of women 25-29 years (aOR 1.71, 95% CI 1.59-1.85). After induction of labor, an intrapartum cesarean section was performed in 37.2% women ≥40 years compared with 20.2% women 25-29 years (aOR 2.51, 95% CI 2.24-2.81). Operative vaginal delivery was performed in 22.6% of women ≥40 years compared with 18.4% women 25-29 years (aOR 1.45, 95% CI 1.28-1.65). The risk of obstetric anal sphincter injury or a 5-minute Apgar score <7 was not increased in women ≥40 years, regardless of onset of labor.

CONCLUSIONS

Trial of labor ended in vaginal delivery in 79% of nulliparous women ≥40 years. The risks of intrapartum cesarean section and operative vaginal delivery were higher in women ≥40 years compared with women 25-29 years, after both spontaneous onset and induction of labor. The risk of obstetric anal sphincter injury or a 5-minute Apgar score <7 was not increased.

Factors associated with intrapartum cesarean section in women aged 40 years or older: a single-center experience in Japan

Objective: To elucidate the efficacy and safety of attempting a vaginal birth and to understand the factors that contribute to the increased risk of operative delivery in women aged 40 years or older.Methods: A database of the Japanese Red Cross Nagoya Daiichi Hospital was reviewed to identify women aged 40 years or older with singleton, vertex, and vital pregnancies who attempted vaginal delivery at and after 37 + 0 gestational weeks between January 2011 and December 2016.Results: A total of 415 women met the criteria for inclusion in this study, including 372 and 43 women who gave birth by vaginal delivery and by intrapartum cesarean section (CS), respectively. Vaginal delivery was observed in 84.1% (201/239) and 97.2% (171/176) of nulliparous and multiparous women, respectively. In a logistic regression model, nulliparity [odds ratio (OR), 5.18; 95% confidence interval (CI), 1.91-14.00], assisted reproductive technology (OR, 2.83; 95% CI, 1.42-5.62), and admission for induction of childbirth (OR, 2.68; 95% CI, 1.08-6.67) were associated with a higher likelihood of intrapartum CS. Of 372 women who delivered vaginally, 62 women needed operative delivery. Operative delivery was necessary for 25.4% (51/201) and 6.4% (11/171) of nulliparous and multiparous women, respectively. A logistic regression model identified nulliparity (OR, 3.91; 95% CI, 1.89-8.08) and administration of ecbolic (OR, 2.49; 95% CI, 1.21-5.10) as being independent factors associated with vacuum extraction.Conclusions: Maternal age 40 years or older should not be a barrier for attempting a vaginal delivery, and those women should be encouraged to attempt a vaginal delivery.

Maternal parity and functional contractility of human myometrium in vitro in the third trimester of pregnancy

OBJECTIVE

It is well established that the duration of the first and second stages of labor are shorter in parous women than in their nulliparous counterparts, a phenomenon not well understood. The aim was to examine the effect of maternal parity on contractile parameters of human myometrium.

DESIGN

Myometrial strips were excised from n = 74 women at cesarean delivery and recordings of contractile activity analyzed and compared across three clinical groups: 1. No previous delivery (P0); 2. One previous delivery (P1); 3. Greater than one previous delivery (P>1).

RESULTS

There was a trend towards greater mean contractile force in the P>1 group than the P1 and P0 groups (P = 0.412). Frequency of contractions was less in the P1 group than in the P0 and P>1 groups(P = 0.027). No differences were observed in relation to all other parameters.

CONCLUSION

Excluding frequency, no intrinsic differences were observed in the functional parameters of human uterine contractions in relation to parity.

Impact of maternal age on intrapartum caesarean delivery rate in nulliparas with spontaneous labour

BACKGROUND

The advanced maternal age rate increases in developed countries. Older women have more pre-existing condition than youngest women and develop more frequently obstetrical pathologies responsible for a higher rate of caesarean delivery before labour and labour induction. For aged nulliparous without pathology who experience spontaneous labour, there is few data on the mode of delivery and on physiological labour according to maternal age.

OBJECTIVE

To compare the intrapartum caesarean delivery rate according to maternal age, for nulliparous with planned vaginal delivery and spontaneous labour at term.

METHODS

Retrospective cohort in a single academic institution between January 2000 and June 2017. All nulliparous women with planned vaginal delivery with live singleton in cephalic presentation at and after 37 weeks of gestation with spontaneous labour were included (n = 10,611). Two groups were compared: nulliparous women aged 20-34 and nulliparous women aged 35 and over. The main outcome was the intrapartum caesarean delivery rate. A subgroup analysis was performed for nulliparous with more advanced maternal age defined as women over 40.

RESULTS

Among the 10,611 women included in this analysis, 8,993 (84.8%) were aged 20-34 and 1,618 (15.2%) were aged over 35. From the latter 367 (22.7%) were over 40 years old. The intrapartum caesarean delivery rate was similar between women aged between 20 and 34 and women aged over 35 (10.8% compared to 8.8%; cOR 0.91, 95% CI 0.76-1.08; aOR 0.91, 95% CI 0.76-1.09). The indications of caesarean were similar in both groups. No differences were found between both groups for mean labour duration (430.9 min for the [20-34] years group compared to 428.0 min for the over 35 years group, p = 0.654). The subgroup analysis performed on nulliparous with more advanced maternal age yielded similar results.

CONCLUSION

For nulliparous at term in spontaneous labour, an advanced maternal age was not associated with an increased intrapartum caesarean delivery rate.

Cesarean section on a rise-Does advanced maternal age explain the increase? A population register-based study

Background

In Denmark, the cesarean section rate has increased by 49% between 1998 and 2015 and accounts for 21% of all births. Cesarean sections may cause short- as well as long-term consequences for both the mother and the child and impose further risks in future pregnancies. Delaying pregnancy until advanced maternal age at childbirth has been suggested as contributing to the increase. The proportion of women giving birth at 35 years or above increased from 15% (1998) to 21% (2015). Advanced maternal age at childbirth has been found to be related to increased pre-pregnancy morbidity and associated risk factors that may contribute to an increased risk of cesarean section. The aim of this study was to examine the association between advanced maternal age and cesarean section in a Danish population and the influence of demographic, anthropometric, health, and obstetric factors on this association.

Methods

This study draws on a national population-based cohort study of all Danish births between 1998 and 2015 (N = 1,122,964). Maternal age less than 30 years serves as reference with the following age categories: (30–34 years); (35–39 years), and (40 years and above). The primary outcome was a cesarean section. Multivariate regression models with adjustment for demographic, health, pregnancy, fetal, and obstetric characteristics were performed with the results further stratified by parity.

Results

In general, a positive association between advanced maternal age and cesarean section was found. Only minor changes in the risk estimate occurred after adjustment for relevant confounders. In comparison with the reference category, nulliparous women aged 35-39- years had twice the risk for cesarean section (adjusted odds ratio (AOR) 2.18, 95% confidence interval (CI) [2.11–2.26]) whereas for women of 40 years or above, the risk was more than tripled (AOR 3.64, 95% CI [3.41–3.90]). For multiparous women aged 35-39-years the risk was more moderate, but still with an AOR of 1.56, 95% CI [1.53–1.60], and for those 40 years and above, the AOR was 2.02, 95% CI [1.92–2.09].

Conclusions

Overall, cesarean section increased with increasing maternal age. Adjustment for maternal and obstetric risk factors had only a minor influence on the association. The association was stronger in nulliparous women compared to multiparous women. Given the lack of impact of demographic and health risks on the relationship between maternal age and cesarean section, the authors suggest obstetric culture could be added to the list of risk factors for a cesarean. Future research on obstetric culture is recommended as are studies on a possible age-related decrease in the ability to maintain the progression of labor.

Trial registration

The study uses depersonalized register data and has been approved by the Danish Data Protection Agency (2015-41-4168).

The Effect of Maternal Age on Obstetric Interventions in a Low-Risk Population

INTRODUCTION

Obstetric interventions appear to increase with advancing maternal age, but limited supporting evidence exists, particularly for young women and specifically for prelabor and intrapartum cesarean birth. The aim of this study was to explore the association between obstetric interventions and maternal age in a low-risk population.

METHODS

The study was restricted to all low-risk, nulliparous women with singleton, vertex, term births who gave birth in Iceland from 1997 to 2015, identified in the Icelandic Medical Birth Registry. Logistic regression models were used to calculate adjusted odds ratios (aORs) and 95% CIs for the risks of labor induction, instrumental birth, and cesarean birth (prelabor and intrapartum), according to maternal age group. All models were adjusted for gestational age, year of birth, and demographic factors, and the models for intrapartum cesarean birth were also adjusted for dystocia and fetal distress.

RESULTS

For women aged more than 40 years, the aOR for induction of labor was 4.69 (95% CI, 3.2-6.8) compared with women aged between 25 and 29 years. In women aged more than 40 years, the increased risks for prelabor cesarean birth and intrapartum cesarean birth were 7.4 (95% CI, 3.0-18.0) and 3.6 (95% CI, 2.1-6.0), respectively. The risk of instrumental birth was slightly increased for women aged between 35 and 39 years (aOR, 1.6; 95% CI, 1.3-2.0), compared with women aged between 25 and 29 years, but not for women aged at least 40 years (aOR, 1.1; 95% CI, 0.7-1.9). For women aged less than 20 years, the risk of induction of labor (aOR, 0.8; 95% CI, 0.7-0.9) and instrumental births (aOR, 0.6; 95% CI, 0.5-0.7) was reduced compared with women aged between 25 and 29 years.

DISCUSSION

The risk of interventions generally increased with increasing maternal age, but the risk of instrumental births was not increased for women aged over 40 years. Also, young women were at a decreased risk of induction of labor and instrumental births.

Maternal body mass index and spontaneous contractility of human myometrium in pregnancy

OBJECTIVE

There is controversy as to whether maternal body mass index (BMI) influences the contractility of human myometrium in pregnancy. The aim of this study was to examine spontaneous contractile activity of human pregnant myometrium in vitro, with respect to maternal BMI.

STUDY DESIGN

Myometrial tissue specimens were obtained at cesarean delivery from 74 women with BMI values ranging from 19 to 50.1 kg m^-2. By recording in vitro from eight strips per donor (590 strips in total), several parameters of spontaneous contractile activity were monitored. The relationship between BMI and contractility was evaluated using linear regression analysis.

RESULTS

There was a significant correlation between maximum amplitude (P=0.007) and mean contractile force (P=0.001) with increasing BMI. However, the time to onset of contractions (P=0.009), and time taken to reach maximal amplitude (P=0.020) also increased with increasing BMI. No significant correlation was observed with BMI for other parameters studied. The mean maximum amplitude value for spontaneous contractions was 37±1 mN, the mean contractile force for spontaneous contractions was 4.1±0.1 mN, the average time to the first spontaneous contraction was 11.3±0.6 min and the average frequency of contractions was 6.5±0.2 per hour.

CONCLUSIONS

These results suggest that the time to onset of contractions is increased with increasing maternal BMI, but that the force developed is greater. In all other respects, human uterine contractility is unaffected by increasing BMI. These findings underline the complexity of regulation of uterine contractility in labor with elevated maternal BMI.