Pathological interactions with the timing of birth and uterine activation

Identification of a novel distension-evoked motility pattern in the mouse uterus

The dynamic changes in uterine contractility in response to distension are incompletely understood. Rhythmic, propagating contractions of nonpregnant uterine smooth muscle occur in the absence of nerve activity (i.e., myogenic), events that decline during pregnancy and reemerge at parturition. We therefore sought to determine how myogenic contractions of the nonpregnant uterus are affected by distension, which might provide mechanistic clues underlying distension-associated uterine conditions such as preterm birth. Uteri isolated from nulliparous adult female mice in proestrus were video imaged to generate spatiotemporal maps, and myoelectrical activity simultaneously recorded using extracellular suction electrodes. Motility patterns were examined under basal conditions and following ramped intraluminal distension with fluid to 5 and 10 cmH₂O. Intraluminal distension caused pressure-dependent changes in the frequency, amplitude, propagation speed, and directionality of uterine contractions, which reversed upon pressure release. Altered burst durations of underlying smooth muscle myoelectric events were concurrently observed, although action potential spike intervals were unchanged. Voltage-gated sodium channel blockade [tetrodotoxin (TTX); 0.6 µM] attenuated both the amplitude of contractions and burst duration of action potentials, whereas all activity was abolished by L-type calcium channel blockade (nifedipine; 1 µM). These data suggest that myogenic motility patterns of the nonpregnant mouse uterus are sensitive to changes in intraluminal pressure and, at high pressures, may be modulated by voltage-gated sodium channel activity. Future studies may investigate whether similar distension-evoked changes occur in the pregnant uterus and the possible pathophysiological role of such activity in the development of preterm birth.

The uterine pacemaker of labor

The laboring uterus is generally thought to initiate contractions much similar to the heart, with a single, dedicated pacemaker. Research on human and animal models over decades has failed to identify such pacemaker. On the contrary, data indicate that instead of being fixed at a site similar to the sinoatrial node of the heart, the initiation site for each uterine contraction changes during time, often with each contraction. The enigmatic uterine "pacemaker" does not seem to fit the standard definition of what a pacemaker should be. The uterine pacemaker must also mesh with the primary physiological function of the uterus - to generate intrauterine pressure. This requires that most areas of the uterine wall contract in a coordinated, or synchronized, manner for each contraction of labor. It is not clear whether the primary mechanism of the uterine pacemaker is a slow-wave generator or an impulse generator. Slow waves in the gut initiate localized smooth muscle contractions. Because the uterus and the gut have somewhat similar cellular and tissue structure, it is reasonable to consider if uterine contractions are paced by a similar mechanism. Unfortunately, there is no convincing experimental verification of uterine slow waves. Similarly, there is no convincing evidence of a cellular mechanism for impulse generation. The uterus appears to have multiple widely dispersed mechanically sensitive functional pacemakers. It is possible that the coordination of organ-level function occurs through intrauterine pressure, thus creating wall stress followed by activation of many mechanosensitive electrogenic pacemakers.

An elevated amniotic fluid prostaglandin F2α concentration is associated with intra-amniotic inflammation/infection, and clinical and histologic chorioamnionitis, as well as impending preterm delivery in patients with preterm labor and intact membranes

OBJECTIVE

To determine whether an elevated amniotic fluid concentration of prostaglandin F2α (PGF2α) is associated with intra-amniotic inflammation/infection and adverse pregnancy outcomes in patients with preterm labor and intact membranes.

MATERIALS AND METHODS

The retrospective cohort study included 132 patients who had singleton pregnancies with preterm labor (< 35 weeks of gestation) and intact membranes. Amniotic fluid was cultured for aerobic and anaerobic bacteria as well as for genital mycoplasmas. Intra-amniotic inflammation was defined by an elevated amniotic fluid matrix metalloproteinase-8 (MMP-8) concentration (>23 ng/mL). PGF2α was measured with a sensitive and specific immunoassay. The amniotic fluid PGF2α concentration was considered elevated when it was above the 95th percentile among pregnant women at 15-36 weeks of gestation who were not in labor (≥170 pg/mL).

RESULTS

(1) The prevalence of an elevated amniotic fluid PGF2α concentration was 40.2% (53/132) in patients with preterm labor and intact membranes; (2) patients with an elevated amniotic fluid PGF2α concentration had a significantly higher rate of positive amniotic fluid culture [19% (10/53) versus 5% (4/79); p = 0.019], intra-amniotic inflammation/infection [49% (26/53) versus 20% (16/79); p = 0.001], spontaneous preterm delivery, clinical and histologic chorioamnionitis, and funisitis, as well as a higher median amniotic fluid MMP-8 concentration and amniotic fluid white blood cell count and a shorter amniocentesis-to-delivery interval than those without an elevated concentration of amniotic fluid PGF2α (p < 0.05 for each); and (3) an elevated amniotic fluid PGF2α concentration was associated with a shorter amniocentesis-to-delivery interval after adjustment for the presence of intra-amniotic inflammation/infection [hazard ratio 2.1, 95% confidence interval (CI) 1.4-3.1; p = 0.001].

CONCLUSION

The concentration of PGF2α was elevated in the amniotic fluid of 40.2% of patients with preterm labor and intact membranes and is an independent risk factor for intra-amniotic inflammation/infection, impending preterm delivery, chorioamnionitis, and funisitis.

Is parturition-timing machinery related to the number of inhibitor CD94/NKG2A positive uterine natural killer cells?

PURPOSE

Prematurity is the most common cause of infant mortality and morbidity. To prevent this, the timing of parturition and its mechanisms should be understood. It is likely that inhibitor CD94/NKG2A positive decidual natural killer cells (uNK) provide for the continuation of pregnancy. Here, we aimed to evaluate whether CD94/NKG2A positive uNK cells are highest in elective cesarian section (C/S) (suggesting ongoing gestation), moderate in normal full-term birth, and lowest in pre-eclamptic parturition.

METHODS

Of 48 pregnant women, 21 C/S, 16 normal, and 11 pre-eclamptic deliveries were included in this study. Five placentas in each group were assigned randomly. After staining, the volumetric analysis of the placental villi and villous blood vessels was performed via the Cavalieri principle. The CD94/NKG2A positive uNK cells were counted using the physical disector method.

RESULTS

The gestation periods and birth weights of the pre-eclamptic deliveries were lower than those of the other two groups. Additionally, the villi and villous vascular volumes were lowest in the pre-eclamptic placentas. As proposed in our hypothesis, the inhibitor CD94/NKG2A positive uNK cells were the highest in the C/S, moderate in the normal, and lowest in the pre-eclamptic placentas.

CONCLUSIONS

These data suggest that CD94/NKG2A positive uNK cells are related with the continuation of pregnancy, and that our human model could be used to search for parturition-timing machinery. We believe that CD94/NKG2A positive uNK cells are also related to the timing of birth.

A novel class of interstitial cells in the mouse and monkey female reproductive tracts

Growing evidence suggests important roles for specialized platelet-derived growth factor receptor alpha-positive (PDGFRalpha(+)) cells in regulating the behaviors of visceral smooth muscle organs. Examination of the female reproductive tracts of mice and monkeys showed that PDGFRalpha(+) cells form extensive networks in ovary, oviduct, and uterus. PDGFRalpha(+) cells were located in discrete locations within these organs, and their distribution and density were similar in rodents and primates. PDGFRalpha(+) cells were distinct from smooth muscle cells and interstitial cells of Cajal (ICC). This was demonstrated with immunohistochemical techniques and by performing molecular expression studies on PDGFRalpha(+) cells from mice with enhanced green fluorescent protein driven off of the endogenous promoter for Pdgfralpha. Significant differences in gene expression were found in PDGFRalpha(+) cells from ovary, oviduct, and uterus. Differences in gene expression were also detected in cells from different tissue regions within the same organ (e.g., uterine myometrium vs. endometrium). PDGFRalpha(+) cells are unlikely to provide pacemaker activity because they lack significant expression of key pacemaker genes found in ICC (Kit and Ano1). Gja1 encoding connexin 43 was expressed at relatively high levels in PDGFRalpha(+) cells (except in the ovary), suggesting these cells can form gap junctions to one another and neighboring smooth muscle cells. PDGFRalpha(+) cells also expressed the early response transcription factor and proto-oncogene Fos, particularly in the ovary. These data demonstrate extensive distribution of PDGFRalpha(+) cells throughout the female reproductive tract. These cells are a heterogeneous population of cells that are likely to contribute to different aspects of physiological regulation in the various anatomical niches they occupy.

Obesity in pregnancy: altered onset and progression of labour

BACKGROUND

the incidence of obesity increases in all developed countries to frightful percentages, also in women of reproductive age. Maternal obesity is associated with important obstetrical complications; and this group also exhibits a higher incidence of prolonged pregnancies and labours.

OBJECTIVE

to review the literature on the pathophysiology of onset and progression of labour in obese woman and translate this knowledge into practical recommendations for clinical management.

METHODS

a literature review, in particular a critical summary of research, in order to determine associations, gaps or inconsistencies in this specific but limited body of research.

FINDINGS

the combination of a higher incidence of post-term childbirths and increased inadequate contraction pattern during the first stage of labour suggests an influence of obesity on myometrial activity. A pathophysiologic pathway for altered onset and progression of labour in obese pregnant women is proposed.

CONCLUSIONS

analysis of the literature shows that obesity is associated with an increased duration of pregnancy and prolonged duration of first stage of labour.

IMPLICATIONS FOR PRACTICE

an adapted clinical approach is suggested in these patients.

Vaginal progesterone vs. cervical cerclage for the prevention of preterm birth in women with a sonographic short cervix, previous preterm birth, and singleton gestation: a systematic review and indirect comparison metaanalysis

OBJECTIVE

No randomized controlled trial has compared vaginal progesterone and cervical cerclage directly for the prevention of preterm birth in women with a sonographic short cervix in the mid trimester, singleton gestation, and previous spontaneous preterm birth. We performed an indirect comparison of vaginal progesterone vs cerclage using placebo/no cerclage as the common comparator.

STUDY DESIGN

Adjusted indirect metaanalysis of randomized controlled trials.

RESULTS

Four studies that evaluated vaginal progesterone vs placebo (158 patients) and 5 studies that evaluated cerclage vs no cerclage (504 patients) were included. Both interventions were associated with a statistically significant reduction in the risk of preterm birth at <32 weeks of gestation and composite perinatal morbidity and mortality compared with placebo/no cerclage. Adjusted indirect metaanalyses did not show statistically significant differences between vaginal progesterone and cerclage in the reduction of preterm birth or adverse perinatal outcomes.

CONCLUSION

Based on state-of-the-art methods for indirect comparisons, either vaginal progesterone or cerclage are equally efficacious in the prevention of preterm birth in women with a sonographic short cervix in the mid trimester, singleton gestation, and previous preterm birth. Selection of the optimal treatment needs to consider adverse events, cost and patient/clinician preferences.

Maternal corticotropin-releasing hormone and the use of selective serotonin reuptake inhibitors independently predict the occurrence of preterm birth

INTRODUCTION

Studies support the premise that chronic maternal stress may trigger a premature sequence of physiologic events ending in preterm birth (PTB). Furthermore, chronic stress is highly correlated with depression and anxiety, which also are associated with PTB. However, some studies report that medication status rather than depression and/or anxiety may reflect the risk for PTB. Although the purpose of this small, preliminary study was to evaluate the association between chronic maternal stress and PTB, this report focuses on the unexpected finding of the association between maternal use of selective serotonin reuptake inhibitors (SSRIs) and PTB.

METHODS

A prospective cohort study of 100 pregnant women included measures of contributors to chronic maternal stress and corticotropin-releasing hormone (CRH). Demographic and behavioral data included smoking, substance use, and use of medications for depression and anxiety.

RESULTS

Pregnant women who used SSRIs to treat depression and/or anxiety were nearly 12 times more likely to give birth before term when compared with women who did not use these medications. Women with CRH levels in the fourth quartile were 6 times more likely to give birth before term when compared with women whose CRH levels were in the lower 3 quartiles. No associations were found between SSRI use and CRH levels.

DISCUSSION

Associations between PTB and maternal use of SSRIs are not understood. It is important not to alter current approaches to the treatment of depression and anxiety without thorough discussion with women regarding the potential benefits and harms of various treatment options.

Secreted surfactant protein A from fetal membranes induces stress fibers in cultured human myometrial cells

In the present study, we investigated the ability of human fetal membranes (amnion and choriodecidua) to regulate human maternal uterine cell functions through the secretion of surfactant protein (SP)-A and SP-D at the end of pregnancy. We detected the expression of both SP-A (SP-A1 and SP-A2) and SP-D by quantitative reverse transcription polymerase chain reaction. Immunohistochemistry revealed that human fetal membranes expressed both SP-A and SP-D. By Western blot analysis, we demonstrated that SP-A protein expression was predominant in choriodecidua, whereas the amnion predominantly expressed SP-D. Only the secretion of SP-A was evidenced in the culture supernatants of amnion and choriodecidua explants by immunodot blot and confirmed by Western blot. Exogenous human purified SP-A induced stress fiber formation in cultured human myometrial cells via a pathway involving Rho-kinase. Conditioned medium from choriodecidua and amnion explants mimicked the SP-A effect. Treatment of myometrial cells with SP-A-depleted conditioned medium from choriodecidua or amnion explants failed to change the actin dynamic. These data indicate that SP-A released by human fetal membranes is able to exert a paracrine regulation of F-actin filament organization in myometrial cells.

Arylsulphatase A activity and sulphatide concentration in placenta, membranes and cord after delivery

AIM

We evaluated variations in behavior of arylsulphatase A activity (an enzyme that catabolizes sulphatides) and of sulphatide concentration in the placenta, cord and membranes of healthy gravidas at term pregnancy, following spontaneous birth.

METHODS

We extracted and biochemically determined arylsulphatase A and sulphatide concentration in placenta, cord and membranes (far from and close to internal uterine os) in 14 patients.

RESULTS

Activity of arylsulphatase A decreased in the cord, in membranes far from the internal uterine os, in membranes close to the internal uterine os and in the placenta. Sulphatide concentration was minimal in the cord and maximal in placenta, with intermediate values in the membranes. No correlation was found between arylsulphatase A activity and sulphatide concentration, nor among arylsulphatase A activities, nor among sulphatide concentrations among the different tissues. It seems that multiparity may increase and the duration of active labor may decrease arylsulphatase A activity in membranes far from the internal uterine os, while active labor duration does not appear to have any implication on sulphatide concentration in membranes close to the internal uterine os.

CONCLUSIONS

Arylsulphatase A activities and sulphatide concentrations in fetal adnexa show significant differences.