Preterm labour. Cervical function and prematurity

Human papillomavirus infection, cervical cancer and the less explored role of trace elements

Cervical cancer is an aggressive type of cancer affecting women worldwide. Many affected individuals rely on smear tests for the diagnosis, surgery, chemotherapy, or radiation for their treatment. However, due to a broad set of undesired results and side-effects associated with the existing protocols, the search for better diagnostic and therapeutic interventions is a never-ending pursuit. In the purview, the bio-concentration of trace elements (copper, selenium, zinc, iron, arsenic, manganese, and cadmium) is seen to fluctuate during the occurrence of cervical cancer and its progression from pre-cancerous to metastatic nature. Thus, during the occurrence of cervical cancer, the detection of trace elements and their supplementation will prove to be highly advantageous in developing diagnostic tools and therapeutics, respectively. This review provides a detailed overview of cervical cancer, its encouragement by human papillomavirus infections, the mechanism of pathology, and resistance. Majorly, the review emphasizes the less explored role of trace elements, their contribution to the growth and inhibition of cervical cancer. Numerous clinical trials have been listed, thereby providing a comprehensive reference to the exploration of trace elements in the management of cervical cancer.

The Role of Neutrophils in Pregnancy, Term and Preterm Labour

Neutrophils are surveillance cells, and the first to react and migrate to sites of inflammation and infection following a chemotactic gradient. Neutrophils play a key role in both sterile inflammation and infection, performing a wide variety of effector functions such as degranulation, phagocytosis, ROS production and release of neutrophil extracellular traps (NETs). Healthy term labour requires a sterile pro-inflammatory process, whereas one of the most common causes of spontaneous preterm birth is microbial driven. Peripheral neutrophilia has long been described during pregnancy, and evidence exists demonstrating neutrophils infiltrating the cervix, uterus and foetal membranes during both term and preterm deliveries. Their presence supports a role in tissue remodelling via their effector functions. In this review, we describe the effector functions of neutrophils. We summarise the evidence to support their role in healthy pregnancy and labour and describe their potential contribution to microbial driven preterm birth.

Transcriptome changes in maternal peripheral blood during term parturition mimic perturbations preceding spontaneous Preterm birth†

The complex physiologic process of parturition includes the onset of labor, which requires the orchestrated stimulation of a common pathway involving uterine contractility, cervical ripening, and chorioamniotic membrane activation. However, the labor-specific processes taking place in these tissues have limited use as predictive biomarkers unless they can be probed in non-invasive samples, such as the peripheral blood. Herein, we utilized a transcriptomic dataset to assess labor-specific changes in the peripheral blood of women who delivered at term. We identified a set of genes that were differentially expressed with labor and enriched for immunological processes, and these gene expression changes were strongly correlated with results from prior studies, providing in silico validation of our findings. We then identified significant correlations between labor-specific transcriptomic changes in the maternal circulation and those reported in the chorioamniotic membranes, myometrium, and cervix of women at term, demonstrating that tissue-specific labor signatures are partly mirrored in the peripheral blood. Last, we demonstrated a significant overlap between the peripheral blood transcriptomic changes in term parturition and those observed in asymptomatic women prior to the diagnosis of preterm prelabor rupture of membranes who delivered preterm. Collectively, we provide evidence that the normal process of labor at term is characterized by a unique immunological expression signature, which may serve as a useful tool for assessing labor status and potentially identifying women at risk for preterm birth.

COL1A1, COL4A3, TIMP2 and TGFB1 polymorphisms in cervical insufficiency

OBJECTIVES

To investigate the association between selected single nucleotide polymorphisms (SNPs) with cervical insufficiency and its relationship with obstetric history.

METHODS

Twenty-eight women with cervical insufficiency (case group) and 29 non-pregnant women (control group) were included. The SNPs sequenced included rs2586490 in collagen type I alpha 1 chain (COL1A1), rs1882435 in collagen type IV alpha 3 chain (COL4A3), rs2277698 in metallopeptidase inhibitor 2 (TIMP2), and rs1800468 in transforming growth factor beta 1 (TGFB1).

RESULTS

We found a higher frequency of the normal allele in the control group (65.5%) and the homozygous mutated genotype in the case group (64.3%) for rs2586490 in COL1A1 (p=0.023). An unplanned finding in the cervical insufficiency group was a higher gestational age of delivery (median≥38 weeks) in the mutated allele than in the wild-type genotype (median of 28.2 weeks) for rs2857396, which is also in the COL1A1 gene (p=0.011).

CONCLUSIONS

The findings of the present study corroborate the hypothesis that cervical insufficiency has a genetic component and probably involves genes encoding proteins in the extracellular matrix, in addition to inflammatory processes.

Pregnancy-specific transcriptional changes upon endotoxin exposure in mice

Objectives Pregnant women are more susceptible to certain infections; however, this increased susceptibility is not fully understood. Herein, systems biology approaches were utilized to elucidate how pregnancy modulates tissue-specific host responses to a bacterial product, endotoxin. Methods Pregnant and non-pregnant mice were injected with endotoxin or saline on 16.5 days post coitum (n=8-11 per group). The uterus, cervix, liver, adrenal gland, kidney, lung, and brain were collected 12 h after injection and transcriptomes were measured using microarrays. Heatmaps and principal component analysis were used for visualization. Differentially expressed genes between groups were assessed using linear models that included interaction terms to determine whether the effect of infection differed with pregnancy status. Pathway analysis was conducted to interpret gene expression changes. Results We report herein a multi-organ atlas of the transcript perturbations in pregnant and non-pregnant mice in response to endotoxin. Pregnancy strongly modified the host responses to endotoxin in the uterus, cervix, and liver. In contrast, pregnancy had a milder effect on the host response to endotoxin in the adrenal gland, lung, and kidney. However, pregnancy did not drastically affect the host response to endotoxin in the brain. Conclusions Pregnancy imprints organ-specific host immune responses upon endotoxin exposure. These findings provide insight into the host-response against microbes during pregnancy.

Role of sex hormones in cervical changes in a cervical excision-related preterm delivery mouse model

Progesterone and oestrogen play important roles during parturition; however, their roles in the uterine cervix during preterm labour and delivery are unknown. We evaluated the serum progesterone and oestrogen levels and changes in their receptors (PR and ER) in the cervix in a cervical excision-associated preterm delivery mouse model. Adult female C57BL/6 mice were divided into four groups: sham, cervical excision (Ex), lipopolysaccharide (LPS) and Ex + LPS. Mating was permitted at 3 weeks post-Ex. On gestation day 16, mice were administered LPS intrauterine (100 µg/100 µL/mouse) or physiological saline (100 µL) via laparotomy. Uterine cervices and blood were sampled immediately postpartum. As a result, epithelial PR and muscular ERα were down- and upregulated, respectively, in the proximal cervix in Ex + LPS group compared to in the sham group. These results indicate that unique sex hormone effects are exerted on the uterine cervix during cervical excision-associated spontaneous preterm labour and delivery.Impact statementWhat is already known on this subject? Preterm and term parturition require the withdrawal of progesterone and the activation of oestrogen in the uterine body and systemic levels. However, we have little understanding of the role of the sex hormones in the uterine cervix.What do the results of this study add? Increased ERα-to-PR expression ratio in the proximal cervix was associated with preterm labour and delivery. ERα expression in the smooth muscle layer of the proximal cervix was higher and PR expression in the proximal cervix epithelium was lower during preterm labour and delivery.What are the implications of these findings for clinical practice and/or further research? This study revealed the differences between the roles of sex hormones and their receptors in epithelial and muscle layers of proximal and distal cervices in preterm labour and delivery.

A Dynamic Compliance Cervix Phantom Robot for Latent Labor Simulation

Physical simulation systems are commonly used in training of midwifery and obstetrics students, but none of these systems offers a dynamic compliance aspect that would make them more truly representative of cervix ripening. In this study, we introduce a unique soft robot phantom that simulates the cervix softening during the latent labor phase of birth. This proof-of-concept robotic phantom can be dilated by 1 cm and effaced by 35% through the application of a Foley catheter-like loading mechanism. Furthermore, psychophysics trials demonstrate how untrained subjects can identify hard and soft states of the phantom with specificities of 91% and 87%, respectively. Both results indicated the appropriateness for application of this soft robot technology to birth training simulators.

Comparative Evaluation of Arabin Pessary and Cervical Cerclage for the Prevention of Preterm Labor in Asymptomatic Women with High Risk Factors

Objective: Preterm labor is one of the most significant obstetric problems associated with high rate of actual and long-term perinatal complications. Despite the creation of scoring systems, uterine activity monitoring, cervical ultrasound and several biochemical markers, the prediction and prevention of preterm labor is still a matter of concern. The aim of this study was to examine cervical findings for the prediction and the comparative use of Arabin pessary or cerclage for the prevention of preterm birth in asymptomatic women with high risk factors for preterm labor. Material and methods: The study group was composed of singleton pregnancies (spontaneously conceived) with high risk factors for preterm labor. Cervical length, dilatation of the internal cervical os and funneling, were estimated with transvaginal ultrasound during the first and the second trimesters of pregnancy. Results: Cervical funneling, during the second trimester of pregnancy, was the most significant factor for the prediction of preterm labor. The use of Arabin cervical pessary was found to be more effective than cerclage in the prolongation of pregnancy. Conclusion: In women at risk for preterm labor, the detection of cervical funneling in the second trimester of pregnancy may help to predict preterm labor and to apply the appropriate treatment for its prevention. Although the use of cervical pessary was found to be more effective than cerclage, more studies are needed to classify the effectiveness of different methods for such prevention.

Differential outcomes of TLR2 engagement in inflammation-induced preterm birth

Preterm birth (PTB) is the leading cause of neonatal mortality worldwide. Infection and inflammation are considered main causes of PTB. Among multiple pathogens, Gram‐positive bacteria are commonly linked with induction of PTB. Although activation of innate immune responses, via TLR2 engagement, by Gram‐positive bacteria is a likely cause, whether induction of PTB depends on the potency of specific microbial components to induce Toll‐like receptor (TLR)2‐driven inflammation has not been elucidated. Here, we show that TLR2 activation by synthetic lipopeptides, Pam2Cys, and Pam3Cys specifically, variably influenced inflammation and subsequent induction of PTB. Pam2Cys challenge, compared to Pam3Cys, induced PTB and promoted significantly higher expression of inflammatory cytokines, specifically IL‐6 and IFN‐β, both in vivo and in vitro. Notably, antibody‐mediated neutralization of IL‐6 or genetic deletion of type I IFN receptor (IFNAR) was sufficient to protect from Pam2Cys‐driven PTB and to temper excessive proinflammatory cytokine production. Conversely, IFN‐β or IL‐6 was not sufficient to promote induction of PTB by Pam3Cys. In summary, our data implies a divergent function of TLR2‐activating lipopeptides in the magnitude and type of ligand‐driven inflammatory vigor in induction of PTB.

Type I interferons regulate susceptibility to inflammation-induced preterm birth

Preterm birth (PTB) is a leading worldwide cause of morbidity and mortality in infants. Maternal inflammation induced by microbial infection is a critical predisposing factor for PTB. However, biological processes associated with competency of pathogens, including viruses, to induce PTB or sensitize for secondary bacterial infection-driven PTB are unknown. We show that pathogen/pathogen-associated molecular pattern-driven activation of type I IFN/IFN receptor (IFNAR) was sufficient to prime for systemic and uterine proinflammatory chemokine and cytokine production and induction of PTB. Similarly, treatment with recombinant type I IFNs recapitulated such effects by exacerbating proinflammatory cytokine production and reducing the dose of secondary inflammatory challenge required for induction of PTB. Inflammatory challenge-driven induction of PTB was eliminated by defects in type I IFN, TLR, or IL-6 responsiveness, whereas the sequence of type I IFN sensing by IFNAR on hematopoietic cells was essential for regulation of proinflammatory cytokine production. Importantly, we also show that type I IFN priming effects are conserved from mice to nonhuman primates and humans, and expression of both type I IFNs and proinflammatory cytokines is upregulated in human PTB. Thus, activation of the type I IFN/IFNAR axis in pregnancy primes for inflammation-driven PTB and provides an actionable biomarker and therapeutic target for mitigating PTB risk.

Reference range of the weekly uterine cervical length at 8 to 38 weeks of gestation in the center of Iran

BACKGROUND

There is an inverse relation between the uterine cervical length during pregnancy and the frequency of preterm delivery. The purpose of this study was to construct a chart and evaluate the cervical length at 8 to 38 weeks of normal gestation in the center of Iran.

MATERIALS AND METHODS

Uterine cervical length was measured on 930 asymptomatic pregnant women by abdominal ultrasonographic technique. For statistical evaluation, regression analysis and calculation of percentiles were performed.

RESULTS

Our data show a significant decrease in uterine cervical length with increasing gestational age. The mean uterine cervical length exhibits minimal changes from 10 to 24 weeks for most women in this study, although the shortening is more prominent at 33 to 38 weeks' gestation. The mean shortening of the uterine cervical length between the second and the ninth months was 14.82% (P < 0.05). Also, the cervical length means in trimesters 1, 2 and 3 were 39.30 ± 4.33, 38.28 ± 5.13 and 36.58 ± 4.58 mm, respectively. The third trimester showed a significant reduction (P < 0.05) in cervical length compared to the first and second trimesters (6.92% and 4.44%, respectively). New charts with the 5(th), 10(th), 50(th), 90(th), and 95(th) percentile are presented.

CONCLUSION

Our study provides a new chart and reference values for normal uterine cervical length throughout gestation based on a large sample in the center of Iran. There was a progressive decrease in mean uterine cervical length with increasing gestational age in the population of this study. Our established charts for uterine cervical length throughout gestation might be more useful than a single cut-off value for more efficient prevention and management of preterm birth.

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.

Placental syncytiotrophoblast maintains a specific type of glycocalyx at the fetomaternal border: the glycocalyx at the fetomaternal interface in healthy women and patients with HELLP syndrome

Recent studies showed that considerable amounts of glycosaminoglycans are released into maternal blood during normal pregnancy and in hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome. Maternal endothelia and the syncytiotrophoblast layer have been discussed as a possible origin of these glycocalyx components. Our study aimed to visualize the glycocalyx on the syncytiotrophoblast by electron microscopy, to analyze its structure and composition by immunohistochemistry, and to determine potential differences between healthy women and women with HELLP syndrome. For electron microscopy, a cotyledon was fixed by perfusion of the intervillous space with a 2% lanthanum-nitrate glutaraldehyde solution followed by immersion fixation in the same fixative. For immunohistochemistry, sections of 16 placentas (HELLP patients/healthy women, n = 8 each) were stained with monoclonal antibodies against the main glycocalyx constituents syndecan 1, hyaluronic acid, and heparan sulfate. Semiquantitative evaluation of staining intensity focused on the apical surface of the syncytiotrophoblast and fetal intravillous endothelia as possible localizations of a placental glycocalyx. Electron microscopy revealed a glycocalyx of approximately 250 nm, covering the syncytiotrophoblast layer. This was found to contain large amounts of syndecan 1, but neither hyaluronic acid nor heparan sulfate as major components. Intravillous fetal endothelium did not express any of the investigated glycosaminoglycans. Healthy women and patients with HELLP showed no differences concerning glycocalyx composition and thickness of the syncytiotrophoblast. The composition of the "placental" glycocalyx differs from the adult and fetal vascular glycocalyx. Obviously, the human placental syncytiotrophoblast maintains a special kind of glycocalyx at the fetomaternal interface.

Time interval from elective removal of cervical cerclage to onset of spontaneous labour

OBJECTIVE

To determine the time interval between elective removal of a cervical cerclage to the onset of spontaneous labour in women who had either a history- or ultrasound-indicated cervical cerclage.

STUDY DESIGN

A retrospective cohort study of women with a singleton pregnancy that had either a modified Shirodkar or McDonald cervical cerclage inserted were evaluated for the time interval between elective cerclage removal and onset of spontaneous labour and also spontaneous labour with 72 h of cervical cerclage removal.

RESULTS

Two hundred and sixty-nine singleton pregnancies with either a modified Shirodkar or McDonald cervical cerclage were analysed. The mean gestational age at cerclage removal was 36.7 ± 1.10 weeks and gestational age at spontaneous labour was 39.0 ± 1.94 weeks (mean ± SD). The median interval between cerclage removal and spontaneous labour was 14 days. Only 18% of women laboured spontaneously within 72 h. Women with ultrasound-indicated cerclage were more likely to deliver within 72 h, compared with women with a history-indicated cervical cerclage (odds ratio, 3.68; 95% confidence interval, 1.31-10.85, p=0.01).

CONCLUSION

Independent of the indication or technique used for cervical cerclage, the rate of early spontaneous labour following elective removal of cervical cerclage is sufficiently low to justify outpatient management.

Obstetric management of moderate and late preterm labour

Moderate and late preterm births account for the majority of preterm babies. The common perception that birth at 32-36 weeks' gestation carries few risks is now being challenged, as these babies have increased risk of neonatal mortality and morbidity. However, spontaneous labour at this gestation frequently has no specific, easily identifiable precursor, although preterm birth per se has a number of epidemiological and clinical associations. Prediction and prevention of preterm birth is currently largely aimed at identifying women at high risk such as those with previous preterm birth, and targeting intervention at this group. Both cervical length assessment and fibronectin testing permit some modification of the likelihood of preterm birth in this group. Progesterone treatment for the prevention of preterm birth is currently being researched widely, and appears a potentially promising strategy. Babies born at 32-36 weeks' gestation need careful monitoring in labour, with modification of intervention in labour due to their prematurity.

Prokineticin 1 induces inflammatory response in human myometrium: a potential role in initiating term and preterm parturition

The infiltration of human myometrium and cervix with leukocytes and the formation of a pro-inflammatory environment within the uterus have been associated with the initiation of both term and preterm parturition. The mechanism regulating the onset of this pro-inflammatory cascade is not fully elucidated. We demonstrate that prokineticin 1 (PROK1) is up-regulated in human myometrium and placenta during labor. The expression of PROK1 receptor remains unchanged during labor and is abundantly expressed in the myometrium. Gene array analysis identified 65 genes up-regulated by PROK1 in human myometrium, mainly cytokines and chemokines, including IL-1β, chemokine C-C motif ligand 3, and colony-stimulating factor 3. In addition, we demonstrate that PROK1 increases the expression of chemokine C-C motif ligand 20, IL-6, IL-8, prostaglandin synthase 2, and prostaglandin E(2) and F(2α) secretion. The treatment of myometrial explants with 100 ng/mL of lipopolysaccharide up-regulates the expression of PROK1, PROK1 receptor, and inflammatory mediators. The infection of myometrial explants with lentiviral microRNA targeting PROK1, preceding treatment with lipopolysaccharide, reduces the expression of inflammatory genes. We propose that PROK1 is a novel inflammatory mediator that can contribute to the onset of human parturition at term and partially mediate premature onset of inflammatory pathways during bacterial infection.

Health disparities in risk for cervical insufficiency

BACKGROUND

The purpose of the study was to examine racial/ethnic differences in cervical insufficiency risk.

METHODS

We used the US 2005 Natality data file. Analysis was limited to singleton births. The prevalence of cervical insufficiency was examined by the maternal characteristic for each racial group. Unconditional logistic regression modeling was used to assess the association between race and cervical insufficiency while controlling for confounders.

RESULTS

Cervical insufficiency risk for Black women was more than twice that for their White counterparts [odds ratio (OR) (95% confidence interval (CI)) of 2.45 (2.22–2.71)]. Prior pregnancy termination showed a dose–response relationship with cervical insufficiency. Compared with women with no history of prior pregnancy termination, primiparous women who have had one pregnancy termination had an OR (95% CI) of 2.49 (2.23–2.77). The OR for two, three and four or more terminations were 4.66 (4.07–5.33), 8.07 (6.77–9.61) and 12.36 (10.19–15.00), respectively. Other predictors of cervical insufficiency included previous preterm birth, parity, marital status, renal disease, history of diabetes, polyhydramnios and anemia.

CONCLUSIONS

There were significant racial/ethnic disparities with Black women having increased cervical insufficiency risk, independent of other studied factors. Prior pregnancy termination is also a major risk factor for cervical insufficiency. The White/Black disparity is evident in both primiparous and multiparous women.

Management strategies for the prevention of preterm birth: Part II - Update on cervical cerclage

PURPOSE OF REVIEW

Cerclage was devised more than 50 years ago based on the hypothesis that for some women, weakness or malfunction of the cervix has a causative role in the pathway to preterm birth (PTB). There have been many theories around the concept of cervical insufficiency but not much in the way of convincing evidence. The purpose of this review was to follow the recent developments in risk identification and prognostication of PTB in connection with appropriately targeted prophylactic interventions.

RECENT FINDINGS

Sonographic cervical length measurement has emerged as an effective prognosticator for PTB in all populations studied so far, independently of obstetric history, consequently deriving a wider applicability than other predictors of PTB. However, the mechanisms leading to cervical shortening are poorly understood, and it cannot be assumed that all cases with a short cervix would benefit from cerclage. Specific conditions may actually reduce the efficacy and advisability of cerclage. For this reason, attempts have been made recently to further characterize the short cervix, leading to the conclusion that only women with a short cervix in the absence of infection/inflammation may be candidates for cerclage. Furthermore, two recent randomized trials of cerclage in women with short cervix on a second trimester ultrasound suggested a benefit with cerclage in PTB rate reduction only in those cases with a cervical length of less than 15 mm.

SUMMARY

The existent literature has treated PTB prevention focusing exclusively on either progesterone use or cerclage, leaving the practitioners without any guidance on when to proceed with medical or surgical prophylaxis. Understanding that high-risk populations are not homogeneous and no single-approach modality is likely to be generally applicable, we have combined the available evidence on both progesterone and cerclage to provide guidance on how to identify subgroups of women at significantly increased risk for PTB and how to preferentially consider progesterone versus cerclage.

Are animal models relevant to key aspects of human parturition?

Preterm birth remains the most serious complication of pregnancy and is associated with increased rates of infant death or permanent neurodevelopmental disability. Our understanding of the regulation of parturition remains inadequate. The scientific literature, largely derived from rodent animal models, suggests two major mechanisms regulating the timing of parturition: the withdrawal of the steroid hormone progesterone and a proinflammatory response by the immune system. However, available evidence strongly suggests that parturition in the human has significantly different regulators and mediators from those in most of the animal models. Our objectives are to critically review the data and concepts that have arisen from use of animal models for parturition and to rationalize the use of a new model. Many animal models have contributed to advances in our understanding of the regulation of parturition. However, we suggest that those animals dependent on progesterone withdrawal to initiate parturition clearly have a limitation to their translation to the human. In such models, a linear sequence of events (e.g., luteolysis, progesterone withdrawal, uterine activation, parturition) gives rise to the concept of a "trigger" mechanism. Conversely, we propose that human parturition may arise from the concomitant maturation of several systems in parallel. We have termed this novel concept "modular accumulation of physiological systems" (MAPS). We also emphasize the urgency to determine the precise role of the immune system in the process of parturition in situations other than intrauterine infection. Finally, we accentuate the need to develop a nonprimate animal model whose physiology is more relevant to human parturition. We suggest that the guinea pig displays several key physiological characteristics of gestation that more closely resemble human pregnancy than do currently favored animal models. We conclude that the application of novel concepts and new models are required to advance translational research in parturition.