Desensitization of oxytocin receptors in human myometrium

The physiology and pharmacology of oxytocin in labor and in the peripartum period

Oxytocin is a reproductive hormone implicated in the process of parturition and widely used during labor. Oxytocin is produced within the supraoptic nucleus and paraventricular nucleus of the hypothalamus and released from the posterior pituitary lobe into the circulation. Oxytocin is released in pulses with increasing frequency and amplitude in the first and second stages of labor, with a few pulses released in the third stage of labor. During labor, the fetus exerts pressure on the cervix of the uterus, which activates a feedforward reflex-the Ferguson reflex-which releases oxytocin. When myometrial contractions activate sympathetic nerves, it decreases oxytocin release. When oxytocin binds to specific myometrial oxytocin receptors, it induces myometrial contractions. High levels of circulating estrogen at term make the receptors more sensitive. In addition, oxytocin stimulates prostaglandin synthesis and release in the decidua and chorioamniotic membranes by activating a specific type of oxytocin receptor. Prostaglandins contribute to cervical ripening and uterine contractility in labor. The oxytocin system in the brain has been implicated in decreasing maternal levels of fear, pain, and stress, and oxytocin release and function during labor are stimulated by a social support. Moreover, studies suggest, but have not yet proven, that labor may be associated with long-term, behavioral and physiological adaptations in the mother and infant, possibly involving epigenetic modulation of oxytocin production and release and the oxytocin receptor. In addition, infusions of synthetic oxytocin are used to induce and augment labor. Oxytocin may be administered according to different dose regimens at increasing rates from 1 to 3 mIU/min to a maximal rate of 36 mIU/min at 15- to 40-minute intervals. The total amount of synthetic oxytocin given during labor can be 5 to 10 IU, but lower and higher amounts of oxytocin may also be given. High-dose infusions of oxytocin may shorten the duration of labor by up to 2 hours compared with no infusion of oxytocin; however, it does not lower the frequency of cesarean delivery. When synthetic oxytocin is administered, the plasma concentration of oxytocin increases in a dose-dependent way: at infusion rates of 20 to 30 mIU/min, plasma oxytocin concentration increases approximately 2- to 3-fold above the basal level. Synthetic oxytocin administered at recommended dose levels is not likely to cross the placenta or maternal blood-brain barrier. Synthetic oxytocin should be administered with caution as high levels may induce tachystole and uterine overstimulation, with potentially negative consequences for the fetus and possibly the mother. Of note, 5 to 10 IU of synthetic oxytocin is often routinely given as an intravenous or intramuscular bolus administration after delivery to induce uterine contractility, which, in turn, induces uterine separation of the placenta and prevents postpartum hemorrhage. Furthermore, it promotes the expulsion of the placenta.

Oxytocin: physiology, pharmacology, and clinical application for labor management

Oxytocin is a peptide hormone that plays a key role in regulating the female reproductive system, including during labor and lactation. It is produced primarily in the hypothalamus and secreted by the posterior pituitary gland. Oxytocin can also be administered as a medication to initiate or augment uterine contractions. To study the effectiveness and safety of oxytocin, previous studies have randomized patients to low- and high-dose oxytocin infusion protocols either alone or as part of an active management of labor strategy along with other interventions. These randomized trials demonstrated that active management of labor and high-dose oxytocin regimens can shorten the length of labor and reduce the incidence of clinical chorioamnionitis. The safety of high-dose oxytocin regimens is also supported by no associated differences in fetal heart rate abnormalities, postpartum hemorrhage, low Apgar scores, neonatal intensive care unit admissions, and umbilical artery acidemia. Most studies reported no differences in the cesarean delivery rates with active management of labor or high-dose oxytocin regimens, thereby further validating its safety. Oxytocin does not have a predictable dose response, thus the pharmacologic effects and the amplitude and frequency of uterine contractions are used as physiological parameters for oxytocin infusion titration to achieve adequate contractions at appropriate intervals. Used in error, oxytocin can cause patient harm, highlighting the importance of precise administration using infusion pumps, institutional safety checklists, and trained nursing staff to closely monitor uterine activity and fetal heart rate changes. In this review, we summarize the physiology, pharmacology, infusion regimens, and associated risks of oxytocin.

Continuous vs intermittent induction of labor with oxytocin in nulliparous patients: a randomized controlled trial

BACKGROUND

Oxytocin is considered the drug of choice for the induction of labor, although the optimal protocol and infusion duration remain to be determined.

OBJECTIVE

This study aimed to assess whether the duration of oxytocin infusion increases 24-hour delivery rates and affects the length of time-to-delivery and patient's experience.

STUDY DESIGN

A randomized controlled trial was performed at a single tertiary medical center, between January 1, 2020 and June 30, 2022. Nulliparous patients with a singleton pregnancy at a vertex presentation and a Bishop score ≥6 were randomly assigned to receive either continuous (16 hours, with a 4 hours pause in between infusions) or intermittent (8 hours, with a 4 hours pause in between infusions) oxytocin infusion, until delivery. In both groups, infusion was halted when signs of maternal or fetal compromise were observed. Randomization was conducted with a computer randomization sequence generation program. The primary outcome was delivery within 24 hours from the first oxytocin infusion and the secondary outcome included time-to-delivery, mode of delivery, and additional maternal and neonatal outcomes. Seventy-two patients per group were randomized to reach 80% statistical power with a 20% difference in the primary outcome according to previous studies.

RESULTS

A total of 153 patients were randomized, 72 to the continuous oxytocin infusion group and 81 to the intermittent infusion group. The total oxytocin infusion time was similar between the groups. Patients in the continuous arm were more likely to deliver within 24 hours from oxytocin initiation (79.73% vs 62.96%, P<.05), and had a shorter oxytocin-to-delivery time interval, compared with patients receiving intermittent treatment (9.3±3.7 hours vs 21±11.7 hours, P<.001). Furthermore, time from ruptured membranes to delivery was shorter (9.3±3.7 hours vs 21±11.7 hours; P<.0001) and chorioamnionitis was less frequent (9.46% vs 21%; P<.05) in the continuous compared with the intermittent arm. Cesarean delivery rate was 20% in both groups (P=.226). There was no difference in postpartum hemorrhage, or adverse neonatal outcomes between the groups. Patients receiving continuous oxytocin infusion were more satisfied with the birthing experience.

CONCLUSION

Continuous infusion of oxytocin for labor induction in nulliparous patients with a favorable cervix may be superior to intermittent oxytocin infusion, because it shortens time-to-delivery, decreases chorioamnionitis rate, and improves maternal satisfaction, without affecting adverse maternal or neonatal outcomes.

Association of oxytocin augmentation and duration of labour with postpartum haemorrhage: A cohort study of nulliparous women

OBJECTIVE

Both duration of labour and use of oxytocin for augmentation are known risk factors for postpartum haemorrhage but distinguishing between the significance of these factors is complex. In this study, we aimed to investigate the association between both labour duration and oxytocin augmentation, for postpartum haemorrhage.

DESIGN

A cohort study based on a secondary analysis of a cluster-randomised trial.

PARTICIPANTS AND SETTING

Term nulliparous women with a single foetus in cephalic presentation, spontaneous onset of active labour and a vaginal birth. The participants were originally included in cluster-randomised trial conducted in Norway from December 1, 2014, to January 31, 2017, that aimed to compare the frequency of intrapartum caesarean sections when adhering to the WHO partograph versus Zhang's guideline.

MEASUREMENTS

The data were analysed through four statistical models. Model 1 investigated the effect of oxytocin augmentation as a dichotomous variable (yes/no); Model 2 investigated the effect of the duration of oxytocin augmentation; Model 3 investigated the effect of the maximum dose of oxytocin; and Model 4 investigated the effect of both the duration of augmentation and the maximum dose of oxytocin. All four models included duration of labour divided into five time-intervals. We used binary logistic regression to estimate the odds ratios of postpartum haemorrhage, defined as blood loss of ≥ 1000 ml, including a random intercept for hospital and mutually adjusting for oxytocin augmentation and labour duration in addition to maternal age, maternal marital status, maternal higher education level, maternal smoking habits in the first trimester, maternal body mass index and birth weight.

FINDINGS

Model 1 found a significant association between the use of oxytocin and postpartum haemorrhage. In Model 2, oxytocin augmentation of ≥ 4.5 h was associated with postpartum haemorrhage. In Model 3, we found an association between a maximum dose of oxytocin of ≥ 20 mU/min and postpartum haemorrhage. Model 4 showed that a maximum dose of oxytocin ≥ 20 mU/min was associated with postpartum haemorrhage both for those augmented < 4.5 h and for those augmented ≥ 4.5 h. Duration of labour was associated with postpartum haemorrhage in all models if lasting ≥ 16 h.

KEY CONCLUSIONS

We found both oxytocin augmentation and labour duration to be associated with postpartum haemorrhage. Oxytocin doses of ≥ 20 mU/min and a labour duration of ≥ 16 h showed an independent association.

IMPLICATION FOR PRACTICE

The potent drug oxytocin should be carefully administered, as doses of ≥ 20 mU/min were associated with an increased risk of PPH, regardless of the duration of oxytocin augmentation.

The In Vitro Contractile Response of Canine Pregnant Myometrium to Oxytocin and Denaverine Hydrochloride

In pregnant bitches, the response to oxytocin and denaverine hydrochloride in dystocia management is usually poor. To better understand the effect of both drugs on myometrial contractility, the circular and longitudinal muscle layers were examined in an organ bath. For each layer, three myometrial strips were stimulated twice, each with one of three oxytocin concentrations. The effect of denaverine hydrochloride was studied once in direct combination with oxytocin and alone with subsequent oxytocin administration. Contractions were recorded and evaluated for average amplitude, mean force, area under the curve (AUC), and frequency. Effects of different treatments were analyzed and compared within and between layers. In the circular layer, oxytocin significantly increased amplitude and mean force compared to untreated controls regardless of stimulation cycles or concentrations. In both layers, high oxytocin concentrations caused tonic contractions, while the lowest concentration created regular rhythmic contractions. Longitudinal layer tissue responded to oxytocin with a significantly decreased contractility when stimulated twice, presumably a sign of desensitization. Denaverine hydrochloride neither affected oxytocin induced contractions nor showed a priming effect to subsequent oxytocin. Thus, no benefit of denaverine hydrochloride on myometrial contractility was found in the organ bath. Our results suggest a better efficiency of low-dose oxytocin in canine dystocia management.

Maternal and newborn plasma oxytocin levels in response to maternal synthetic oxytocin administration during labour, birth and postpartum - a systematic review with implications for the function of the oxytocinergic system

BACKGROUND

The reproductive hormone oxytocin facilitates labour, birth and postpartum adaptations for women and newborns. Synthetic oxytocin is commonly given to induce or augment labour and to decrease postpartum bleeding.

AIM

To systematically review studies measuring plasma oxytocin levels in women and newborns following maternal administration of synthetic oxytocin during labour, birth and/or postpartum and to consider possible impacts on endogenous oxytocin and related systems.

METHODS

Systematic searches of PubMed, CINAHL, PsycInfo and Scopus databases followed PRISMA guidelines, including all peer-reviewed studies in languages understood by the authors. Thirty-five publications met inclusion criteria, including 1373 women and 148 newborns. Studies varied substantially in design and methodology, so classical meta-analysis was not possible. Therefore, results were categorized, analysed and summarised in text and tables.

RESULTS

Infusions of synthetic oxytocin increased maternal plasma oxytocin levels dose-dependently; doubling the infusion rate approximately doubled oxytocin levels. Infusions below 10 milliunits per minute (mU/min) did not raise maternal oxytocin above the range observed in physiological labour. At high intrapartum infusion rates (up to 32 mU/min) maternal plasma oxytocin reached 2-3 times physiological levels. Postpartum synthetic oxytocin regimens used comparatively higher doses with shorter duration compared to labour, giving greater but transient maternal oxytocin elevations. Total postpartum dose was comparable to total intrapartum dose following vaginal birth, but post-caesarean dosages were higher. Newborn oxytocin levels were higher in the umbilical artery vs. umbilical vein, and both were higher than maternal plasma levels, implying substantial fetal oxytocin production in labour. Newborn oxytocin levels were not further elevated following maternal intrapartum synthetic oxytocin, suggesting that synthetic oxytocin at clinical doses does not cross from mother to fetus.

CONCLUSIONS

Synthetic oxytocin infusion during labour increased maternal plasma oxytocin levels 2-3-fold at the highest doses and was not associated with neonatal plasma oxytocin elevations. Therefore, direct effects from synthetic oxytocin transfer to maternal brain or fetus are unlikely. However, infusions of synthetic oxytocin in labour change uterine contraction patterns. This may influence uterine blood flow and maternal autonomic nervous system activity, potentially harming the fetus and increasing maternal pain and stress.

Oxytocin receptor DNA methylation is associated with exogenous oxytocin needs during parturition and postpartum hemorrhage

BACKGROUND

The oxytocin receptor gene (OXTR) is regulated, in part, by DNA methylation. This mechanism has implications for uterine contractility during labor and for prevention or treatment of postpartum hemorrhage, an important contributor to global maternal morbidity and mortality.

METHODS

We measured and compared the level of OXTR DNA methylation between matched blood and uterine myometrium to evaluate blood as an indicator of uterine methylation status using targeted pyrosequencing and sites from the Illumina EPIC Array. Next, we tested for OXTR DNA methylation differences in blood between individuals who experienced a postpartum hemorrhage arising from uterine atony and matched controls following vaginal birth. Bivariate statistical tests, generalized linear modeling and Poisson regression were used in the analyses.

RESULTS

Here we show a significant positive correlation between blood and uterine DNA methylation levels at several OXTR loci. Females with higher OXTR DNA methylation in blood had required significantly more exogenous oxytocin during parturition. With higher DNA methylation, those who had oxytocin administered during labor had significantly greater relative risk for postpartum hemorrhage (IRR 2.95, 95% CI 1.53-5.71).

CONCLUSIONS

We provide evidence that epigenetic variability in OXTR is associated with the amount of oxytocin administered during parturition and moderates subsequent postpartum hemorrhage. Methylation can be measured using a peripheral tissue, suggesting potential use in identifying individuals susceptible to postpartum hemorrhage. Future studies are needed to quantify myometrial gene expression in connection with OXTR methylation.

Involvement of Oxytocin and Progesterone Receptor Expression in the Etiology of Canine Uterine Inertia

An altered oxytocin and progesterone receptor (OXTR and PGR, respectively) expression was postulated in canine uterine inertia (UI), which is the lack of functional myometrial contractions. OXTR and PGR expressions were compared in uterine tissue obtained during C-section due to primary UI (PUI; n = 12) and obstructive dystocia (OD, n = 8). In PUI, the influence of litter size was studied (small/normal/large litter: PUI-S/N/L: n = 5/4/3). Staining intensity in immunohistochemistry was scored for the longitudinal and circular myometrial layer and summarized per dog (IP-Myoscore). Mean P4 did not differ significantly between PUI (n = 9) and OD (n = 7). OXTR and PGR expressions (ratios) were significantly higher in PUI (OXTR: p = 0.0019; PGR: p = 0.0339), also for OXTR in PUI-N versus OD (p = 0.0034). A trend for a higher PGR IP-Myoscore was identified (PUI-N vs. OD, p = 0.0626) as well as an influence of litter size (lowest PGR-Myoscore in PUI-L, p = 0.0391). In conclusion, PUI was not related to higher P4, but potentially increased PGR availability compared to OD. It remains to be clarified whether OXTR is upregulated in PUI due to a counterregulatory mechanism to overcome myometrial quiescence or downregulated in OD due to physiological slow OXTR desensitization associated with an advanced duration of labor. Identified OXTR differences between myometrial layers indicate the need for further research.

Continued versus discontinued oxytocin after the active phase of labor: An updated systematic review and meta-analysis

Objective

To systematically assess the effect of discontinued vs continued oxytocin after active stage of labour is established.

Methods

Pubmed, Embase, and the Cochrane Library were systematically searched to 18 April 2021. The risk ratio or mean difference with corresponding 95% confidence interval were computed to investigate the effect of intervention or control on maternal and fetus outcomes. This review was registered in the International Prospective Register of Systematic Reviews: CRD42021249635.

Results

Discontinuing oxytocin when the active labour was established might decrease the risk of cesarean delivery [RR (95% CI): 0.84 (0.72–0.98), P = 0.02]. However, when we restricted our analysis to women who performed cesarean section after the active phase was reached, the difference was no longer significant [RR (95% CI): 0.82 (0.60–1.10), P = 0.19]. The incidence of uterine tachysystole [RR (95% CI): 0.36 (0.27–0.49)], postpartum hemorrhage [RR (95% CI): 0.78 (0.65–0.93)], and non-reassuring fetal heart rate [RR (95% CI): 0.66 (0.58–0.76)] were significantly lower in the oxytocin discontinuation group. We also found a possible decrease in the risk of chorioamnionitis in discontinued oxytocin group [RR (95% CI): 2.77 (1.02–5.08)]. An increased duration of active [MD (95% CI): 2.28 (2.86–41.71)] and second [MD (95% CI): 5.36 (3.18–7.54)] phase of labour was observed in discontinued oxytocin group, while the total delivery time was not significantly different [MD (95% CI): 20.17 (-24.92–65.26)].

Conclusion

After the active labor is reached, discontinuation of oxytocin could be considered a new recommendation for the improved maternal and fetal outcomes without delaying labour.

Birth with synthetic oxytocin and the risk of being overweight or obese during childhood

BACKGROUND

Despite the importance of oxytocinergic signalling for satiety regulation and energy balance, the impact of exposure to synthetic oxytocin during childbirth on obesity during childhood remains unknown.

OBJECTIVES

To examine the association between oxytocin exposure during labour and the risk of being overweight or obese during childhood.

METHODS

Synthetic oxytocin exposure data of mothers from the Danish Medical Birth Registry were linked with self-reported anthropometric data of their children from the Danish National Birth Cohort (5 months-11 years of age). Multinomial logistic regression and latent class growth analyses were performed to determine the association between oxytocin exposure and obesity during childhood.

RESULTS

With the exception of the normal weight-to-overweight group between ages 5 and 12 months, none of the other analyses revealed a significant association between synthetic oxytocin use and the risk of being overweight until the age of 11 years. Furthermore, latent class growth analysis did not reveal an association between oxytocin exposure at birth and the risk of being overweight or obese during childhood.

CONCLUSIONS

Our analysis of a large cohort of children who varied in their synthetic oxytocin exposure status at childbirth did not reveal an association between oxytocin exposure and the risk of childhood overweight/obesity.

Maternal oxytocin administration modulates gene expression in the brains of perinatal mice

OBJECTIVES

Oxytocin (OXT) is widely used to facilitate labor. However, little is known about the effects of perinatal OXT exposure on the developing brain. We investigated the effects of maternal OXT administration on gene expression in perinatal mouse brains.

METHODS

Pregnant C57BL/6 mice were treated with saline or OXT at term (n=6-7/group). Dams and pups were euthanized on gestational day (GD) 18.5 after delivery by C-section. Another set of dams was treated with saline or OXT (n=6-7/group) and allowed to deliver naturally; pups were euthanized on postnatal day 9 (PND9). Perinatal/neonatal brain gene expression was determined using Illumina BeadChip Arrays and real time quantitative PCR. Differential gene expression analyses were performed. In addition, the effect of OXT on neurite outgrowth was assessed using PC12 cells.

RESULTS

Distinct and sex-specific gene expression patterns were identified in offspring brains following maternal OXT administration at term. The microarray data showed that female GD18.5 brains exhibited more differential changes in gene expression compared to male GD18.5 brains. Specifically, Cnot4 and Frmd4a were significantly reduced by OXT exposure in male and female GD18.5 brains, whereas Mtap1b, Srsf11, and Syn2 were significantly reduced only in female GD18.5 brains. No significant microarray differences were observed in PND9 brains. By quantitative PCR, OXT exposure reduced Oxtr expression in female and male brains on GD18.5 and PND9, respectively. PC12 cell differentiation assays revealed that OXT induced neurite outgrowth.

CONCLUSIONS

Prenatal OXT exposure induces sex-specific differential regulation of several nervous system-related genes and pathways with important neural functions in perinatal brains.

Temporal Dynamics of Intranasal Oxytocin in Human Brain Electrophysiology

Oxytocin (OT) is a key modulator of human social cognition, popular in behavioral neuroscience. To adequately design and interpret intranasal OT (IN-OT) research, it is crucial to know for how long it affects human brain function once administered. However, this has been mostly deduced from peripheral body fluids studies, or uncommonly used dosages. We aimed to characterize IN-OT’s effects on human brain function using resting-state EEG microstates across a typical experimental session duration. Nineteen healthy males participated in a double-blind, placebo-controlled, within-subject, cross-over design of 24 IU of IN-OT in 12-min windows 15 min-to-1 h 42min after administration. We observed IN-OT effects on all microstates, across the observation span. During eyes-closed, IN-OT increased duration and contribution of A and contribution and occurrence of D, decreased duration and contribution of B and C; and increased transition probability C-to-B and C-to-D. In eyes-open, it increased A-to-C and A-to-D. As microstates A and D have been related to phonological auditory and attentional networks, respectively, we posit IN-OT may tune the brain for reception of external stimuli, particularly of social nature—tentatively supporting current neurocognitive hypotheses of OT. Moreover, we contrast our overall results against a comprehensive literature review of IN-OT time-course effects in the brain, highlighting comparability issues.

Cervical Ripening and Labor Induction and Augmentation, 5th Edition

Cervical ripening and induction and augmentation of labor are common procedures in labor and birth units. The potential risks and benefits for the procedure should be explained to women so that they can make informed decisions. Clinicians should be knowledgeable about the methods and medications used and be skilled in maternal-fetal assessment. Adequate nurse staffing is required to monitor the mother and fetus to promote the best possible outcomes. This practice monograph includes information on mechanical and pharmacologic methods for cervical ripening; labor induction and augmentation with oxytocin, a high alert drug; and nurse staffing levels and skills needed to provide safe and effective care during cervical ripening and labor induction and augmentation.

The Effects of Nitroglycerin on the Oxytocin Dose-Response Profile in Oxytocin-Desensitized and Naïve Human Myometrium: An In Vitro Study

BACKGROUND

Nitroglycerin is used for acute reduction in uterine tone. Prolonged oxytocin exposure causes desensitization of oxytocin receptors. It is unknown if nitroglycerin exposure impacts the subsequent action of oxytocin in the setting of oxytocin receptor desensitization. This study investigated the effects of nitroglycerin on oxytocin-desensitized and oxytocin-naïve human myometrium and the subsequent response to oxytocin dose-response testing in vitro.

METHODS

Myometrial samples from 17 elective cesarean deliveries were divided into strips and allocated to 1 of 4 groups: (1) oxytocin desensitized and no nitroglycerin; (2) oxytocin desensitized and nitroglycerin; (3) oxytocin naïve and nitroglycerin; and (4) oxytocin naïve and no nitroglycerin. Final analysis included 28 strips per group. Nitroglycerin groups were exposed to incremental concentrations of nitroglycerin, while no nitroglycerin groups were kept in control (physiological salt) solution. All groups then underwent oxytocin dose-response testing. Primary outcome was motility index (amplitude × frequency; grams × contractions per 10 minutes [g·c/10 min]). Secondary outcomes were amplitude (g), frequency (contractions/10 minutes), and area under the curve (g·s). All outcomes (nitroglycerin and oxytocin dose-response periods) were expressed as a percentage change from baseline. Values were log transformed, compared using regression modeling and reported as the ratio of 2 geometric means (relative difference).

RESULTS

No significant difference was observed in motility index following nitroglycerin administration in oxytocin-desensitized versus oxytocin-naïve groups (relative difference = 19.0%; 95% confidence interval [CI], -32.6 to 109.9; P = .55). On oxytocin dose-response testing, motility index was highest in oxytocin-naïve and no nitroglycerin samples (group 4) (1.356 g·c/10 minutes) followed by oxytocin-naïve and nitroglycerin (group 3) (0.882 g·c/10 minutes), oxytocin-desensitized and no nitroglycerin (group 1) (0.769 g·c/10 minutes), and oxytocin-desensitized and nitroglycerin (group 2) (0.651 g·c/10 minutes) samples. Motility index was significantly reduced in group 1 vs 4 (relative difference = -43.3%; 95% CI, -66.5 to -4.1; P = .034) and group 2 vs 4 (relative difference = -52.0%; 95% CI, -70.9 to -20.8; P = .004). While in groups 3 vs 4, both amplitude (relative difference = -17.8%; 95% CI, -30.9 to -2.2; P = .27) and area under the curve (AUC; relative difference = -17.5%; 95% CI, -30.7 to -1.8; P = .030) were reduced.

CONCLUSIONS

Nitroglycerin-induced relaxation was not different between oxytocin-desensitized and oxytocin-naïve human myometrial strips in vitro. However, oxytocin-induced contractility was attenuated after nitroglycerin exposure in both oxytocin-desensitized and oxytocin-naïve samples, with maximum attenuation observed in desensitized tissues. This finding warrants further clinical studies to explore uterine responsiveness to oxytocin in women with oxytocin-augmented labors after nitroglycerin administration.

Changes in cAMP effector predominance are associated with increased oxytocin receptor expression in twin but not infection-associated or idiopathic preterm labour

We previously reported that at term pregnancy, a decline in myometrial protein kinase A (PKA) activity leads to an exchange protein activated by cyclic AMP (Epac1)-dependent increase in oxytocin receptor (OTR) expression, promoting the onset of labour. Here, we studied the changes in the cyclic adenosine monophosphate (cAMP) effector system present in different phenotypes of preterm labour (PTL). Myometrial biopsies obtained from women with phenotypically distinct forms of PTL and the levels of PKA and OTR were examined. Although we found similar changes in the cAMP effector pathway in all forms of PTL, only in the case of twin PTL (T-PTL) was myometrial OTR levels increased in association with these results. Although there were several changes in the mRNA levels of components of the cAMP synthetic pathway, the total myometrial cAMP levels did not change with the onset of any subtype of PTL. With regards to the expression of cAMP-responsive genes, we found that the mRNA levels of 4 of the 5 cAMP-down-regulated genes were increased in T-PTL, similar to our findings in term labour. These data signify that although changes in the cAMP effector system were common to all forms of PTL, only in T-PTL were OTR levels increased. Similarly, the mRNA levels of cAMP-repressed genes were only increased in T-PTL supporting the concept that the decline in PKA levels influences myometrial function driving the onset of T-PTL.

Cervical Ripening and Labor Induction and Augmentation, 5th Edition

Cervical ripening and induction and augmentation of labor are common procedures in labor and birth units. The potential risks and benefits for the procedure should be explained to women so that they can make informed decisions. Clinicians should be knowledgeable about the methods and medications used and be skilled in maternal-fetal assessment. Adequate nurse staffing is required to monitor the mother and fetus to promote the best possible outcomes. This practice monograph includes information on mechanical and pharmacologic methods for cervical ripening; labor induction and augmentation with oxytocin, a high alert drug; and nurse staffing levels and skills needed to provide safe and effective care during cervical ripening and labor induction and augmentation.

Effects of Intermittent and Continuous Oxytocin Exposure on Myometrial Contractile Activity in Term-Pregnant Rats In Vitro

Continuous oxytocin exposure to augment labor contractions may cause receptor desensitization and further reduce the uterine response to oxytocin, resulting in an increased risk of uterine atony. This study aimed to investigate and compare the uterine response to continuous and intermittent oxytocin stimulation. We hypothesized that intermittent brief episodes of oxytocin separated by recovery periods rather than continuous oxytocin application improves subsequent uterine contractions. Myometrial strips were isolated from term-pregnant rats (22 days of gestation; n = 11), mounted in tissue bath chambers, and exposed to continuous oxytocin (5 nM) for 2 h or 6 repeated episodes of 10-min oxytocin exposure (5 nM) separated by 10 min of recovery period in Krebs solution. Contractile parameters (force amplitude, frequency, and integral force) significantly decreased during continuous oxytocin exposure compared with control (n = 11; P < 0.01). Interestingly, myometrial contractility significantly increased during subsequent short intermittent oxytocin exposure which was sustained for 6 h compared with control or continuous exposure (n = 11; P < 0.01). Brief intermittent oxytocin stimulations resulted in better uterine response and improved contractile force than continuous exposure, which may be attributed to attenuation of receptor desensitization or recovery of oxytocin receptor function following intermittent exposure. These findings would help maintain adequate strong contractions to avoid postpartum bleeding.

The Effect of Intermittent Oxytocin Pretreatment on Oxytocin-Induced Contractility of Human Myometrium In Vitro

BACKGROUND

Prolonged continuous oxytocin administration during labor may induce oxytocin receptor desensitization, which attenuates the response of the myometrium to further oxytocin, increasing the risk of postpartum hemorrhage. The literature comparing pulsatile (intermittent) versus continuous oxytocin administration for induction and augmentation of labor is inconsistent with regard to maternal outcomes. We aimed to determine the effect of intermittent versus continuous oxytocin preexposure on myometrial responsiveness to subsequent oxytocin. We hypothesized that intermittent oxytocin pretreatment would result in superior subsequent oxytocin-induced contractility than continuous oxytocin pretreatment.

METHODS

This in vitro study was undertaken using myometrium obtained from women undergoing elective cesarean deliveries. Each myometrial strip was mounted in an individual organ bath with physiological salt solution under homeostatic conditions and allocated to one of 3 groups: (1) control (no pretreatment); (2) continuous (pretreatment with oxytocin 10(-5) M for 2 hours); or (3) intermittent (pretreatment with alternating oxytocin 10 M and physiological salt solution every 15 minutes, for 2 hours). After pretreatment, dose-response testing to oxytocin 10(-5) to 10(-5) M was performed and contractile parameters were measured. The primary outcome was motility index (MI, amplitude × frequency) of contractions.

RESULTS

Eighteen women were recruited, and 86 successful experiments were performed (control n = 29, continuous n = 28, intermittent n = 29). The means (standard errors) of MI (√g·contractions/10 min) in the control, continuous, and intermittent groups were 2.34 (0.09), 1.78 (0.09), and 2.13 (0.11), respectively. The MI was significantly reduced in the continuous group when compared to the control (estimated difference [95% confidence interval {CI}], -0.56 [-0.81 to -0.31]; P < .01) and intermittent group (estimated difference [95% CI], -0.35 [-0.62 to -0.08]; P = .01). There was no significant difference in MI between the intermittent and control group (estimated difference [95% CI], -0.21 [-0.51 to 0.09]; P = .17).

CONCLUSIONS

Human myometrium remains more responsive to subsequent oxytocin after intermittent compared to continuous exposure to oxytocin, most likely due to reduction in oxytocin receptor desensitization, or facilitation of receptor resensitization in the intermittent group. Hence, intermittent oxytocin administration during labor warrants further investigation as a technique to preserve uterine oxytocin responsiveness.

Risk factors for severe postpartum haemorrhage: A population-based retrospective cohort study

BACKGROUND

Severe postpartum haemorrhage (PPH) is a serious clinical problem that is increasing in incidence.

AIM

To identify risk factors for severe PPH.

MATERIALS AND METHODS

Population-based retrospective cohort study of all women who gave birth in Victoria in 2009-2013 using the validated Victorian Perinatal Data Collection. Three multivariable logistic regression models estimated the adjusted risk of severe PPH. Adjusted odds ratios (aOR) and their 95% confidence intervals are reported. The primary outcome was severe PPH (estimated blood loss of ≥1500 mL).

RESULTS

Severe PPH occurred in 1.4% of all births (n = 5122). Maternal characteristics significantly associated with severe PPH included: multiple pregnancy; older maternal age; overweight/obesity; first births. Other risk factors included placental complications, macrosomia, instrumental vaginal birth, third and fourth degree perineal lacerations, in-labour caesarean section, birth at a gestation other than 37-41 weeks, duration of labour 12 to <24 h, and use of oxytocin infusions in labour. Planned pre-labour caesarean section was associated with reduced odds of severe PPH. Severe PPH also occurred in 0.7% (n = 104) of women with none of the identified risk factors.

CONCLUSIONS

Numerous risk factors for severe PPH are identified but some cases are not modifiable or predictable. Limiting use of oxytocin infusions in labour to cases with clear indications, and strategies to prevent severe perineal lacerations would prevent some severe PPHs. Close surveillance of all women in the hours immediately following birth is crucial to detect and manage excessive blood loss and reduce severe PPH and associated morbidity.

What does basic science tell us about the use of uterotonics?

Pharmacotherapy with uterotonics remains the mainstay of the management for post-partum haemorrhage. Clinical studies evaluating the efficacy of these drugs are fraught with confounders, which may influence uterine contractility and blood loss. For this reason, a range of techniques have been developed to study myometrial function in vitro, allowing for the comparison of various drugs in a controlled-simulated physiological environment. In this review, we focus on the main classes of uterotonic drugs and outline their molecular and physiological basis of action. We explore the evidence related to appropriate drug dosing and relative efficacy, and compare the evidence gleaned from clinical and in vitro studies. We discuss the mechanism of oxytocin desensitisation and how basic science has helped us understand this phenomenon. We also discuss the in vitro research findings for each of the main classes of uterotonic drugs that have contributed to an improved understanding of the management of post-partum haemorrhage and, ultimately, better care for mothers.

Association between time from cessation of oxytocin infusion for labor to delivery and intraoperative severe blood loss during cesarean section: a retrospective cohort study

Aim: Prolonged oxytocin infusion during labor results in receptor desensitization and increases the risk of obstetric hemorrhage. We aimed to examine the association between recovery time (RT) and intraoperative severe blood loss in women who underwent a cesarean section after oxytocin pretreatment.Methods: We retrospectively assessed 103 Japanese women who underwent cesarean section after oxytocin pretreatment. RT (time from cessation of oxytocin infusion during labor to delivery) and intraoperative severe blood loss (active bleeding exceeding 1000 mL) were measured. Confounding factors were controlled, and RT cut-off value associated with severe blood loss and association between RT and intraoperative severe blood loss were assessed.Results: The mean maternal age was 34 years, and 100 (97.1%) women delivered at term. Mean RT was 121.6 min. The overall incidence of intraoperative severe blood loss was 22.3% (23/103). The cut-off point to predict intraoperative severe blood loss was 96 min (sensitivity, 65.2%; specificity, 81.3%). On multivariate analysis, an RT of ≤96 min [adjusted odds ratio (OR), 11.9; 95% confidence interval (CI), 3.32-42.7] and macrosomia (adjusted OR, 3.91; 95% CI, 1.10-13.8) were associated with intraoperative severe blood loss.Conclusions: Consideration of RT is helpful in the management of women undergoing cesarean section after oxytocin pretreatment.

Oxytocin discontinuation after the active phase of induced labor: A systematic review

BACKGROUND

Oxytocin is the most widely used drug in the induction of labor, but it could have potential adverse effects that derive from uterine hyperstimulation.

AIM

To determine the benefits and drawbacks of oxytocin continuation versus oxytocin discontinuation after the active phase of induced labor.

METHODS

We systematically searched Pubmed, EMBASE, Scopus, ClinicalTrials.gov and Cochrane Library Plus until October 2017, for randomized controlled trials comparing oxytocin continuation with oxytocin discontinuation when the active phase of labor is reached were included. Data was collected by three reviewers and quality of the included studies assessed using the methodology recommended in the Cochrane Handbook. StatsDirect software was used to calculate risk ratios for binary variables and weighted mean differences for continuous variables. A fixed-effects or random-effects model was used as appropriate.

RESULTS

Nine studies were selected including 1538 women, 774 in the oxytocin continuation group and 764 in the oxytocin discontinuation group. The incidence of cesarean sections (14.3% vs. 8.6%; relative risk, 1.67; 95% confidence interval: 1.25-2.23), uterine hyperstimulation (12.4% vs. 4.7%; relative risk, 2.59; 95% confidence interval: 1.70-3.93) and nonreassuring fetal heart rate (19.2% vs.12.5%; relative risk, 1.55; 95% confidence interval: 1.18-2.02) were significantly higher in the oxytocin continuation group. An increase in the duration of the second stage of labor in the oxytocin discontinuation group was observed (pooled mean difference, -7.03; 95% confidence interval: -9.80 to -4.26).

CONCLUSIONS

After the active phase of induced labor, oxytocin continuation increases the risk of cesarean section, uterine hyperstimulation and alterations to the fetal heart rate.

Oxytocin Use in Labor: Legal Implications

Oxytocin is one of the most commonly used medications in obstetrics and has been associated with claims of negligence in cases of adverse outcomes. Errors involving intravenous oxytocin administration for induction or augmentation of labor are most commonly dose related and include failure to avoid or treat tachysystole or failure to asses or treat a fetal heart rate pattern indicative of disruption in oxygenation. Clinicians should be knowledgeable regarding pharmacokinetics of oxytocin and the effect of uterine contractions on fetal oxygenation as well as safe titration of oxytocin to achieve the desired effect while minimizing harm.

The association between the time from oxytocin cessation during labour to Cesarean delivery and postpartum blood loss: a retrospective cohort study

PURPOSE

Prolonged exposure to oxytocin during augmentation of labour is associated with uterine atony and an increased risk of postpartum hemorrhage (PPH) due to oxytocin receptor desensitization. Cessation of oxytocin infusion during labour may facilitate recovery of oxytocin receptor function, which then helps to restore myometrial contractility and decrease postpartum blood loss. We examined the association between oxytocin recovery interval, i.e., the time from discontinuing oxytocin to Cesarean delivery (CD) for labour arrest, and blood loss.

METHODS

This retrospective cohort study included women who underwent CD for labour arrest following oxytocin-augmented labour from July 1, 2013 to July 19, 2015 at our institution. Data were collected on patient demographics, labour and delivery characteristics, oxytocin induction and augmentation, recovery interval, and PPH risk factors. The primary outcome was estimated blood loss (EBL), calculated using the hematocrit variation method.

RESULTS

Data on 490 women were analyzed. The mean (standard deviation) EBL was 1,341 (577) mL; the amount of oxytocin administered during labour was 6,447 (6,868) mU, and the oxytocin recovery interval was 99 (65) min. Every ten-minute increase in the recovery interval was associated with a 10-mL decrease in EBL (95% confidence interval [CI], -18 to -3; P = 0.009). Morbidly obese women had a significantly higher EBL than those with a body mass index < 40 kg·m^-2 (mean difference, 572 mL; 95% CI, 382 to 762; P < 0.001). The amount and duration of oxytocin administered during labour, but not the oxytocin recovery interval, was associated with the use of additional interventions to control PPH (P = 0.005).

CONCLUSION

Our study shows that an increase in the oxytocin recovery interval is associated with a decrease in blood loss at CD in women with oxytocin augmented labour. These data support discontinuing the oxytocin infusion as soon as the decision is made to proceed with CD for labour arrest, particularly in morbidly obese women.

The Recovery Time of Myometrial Responsiveness After Oxytocin-Induced Desensitization in Human Myometrium In Vitro

BACKGROUND

Postpartum hemorrhage secondary to uterine atony is a leading cause of maternal morbidity. Prolonged exposure to oxytocin for labor augmentation can result in the desensitization phenomenon, a decrease in the responsiveness of myometrium to further oxytocin. It is currently not known whether waiting for a specific time interval after the cessation of oxytocin allows the oxytocin receptors to resensitize and recover, thereby improving subsequent oxytocin-induced myometrial contractility. We aimed to investigate the effect of a rest period of 30, 60, and 90 minutes after oxytocin administration on the recovery of oxytocin-desensitized human myometrium in vitro. We hypothesized that the longer the rest period, the better the responsiveness and subsequent oxytocin-induced contractility of the myometrium.

METHODS

Myometrial tissue was obtained from women undergoing elective cesarean deliveries. The myometrial sample was dissected into 4 strips, and each strip was mounted in a single organ bath with physiological salt solution (PSS) under homeostatic conditions and then pretreated for 2 hours with oxytocin 10 M. After pretreatment, each strip was washed with PSS and allowed to rest in PSS solution for 30, 60, or 90 minutes. At the end of the rest period, dose-response testing to oxytocin 10 to 10 M was performed. A control group consisted of oxytocin dose-response testing without any oxytocin pretreatment. Contractile parameters were measured and compared among the groups after square root transformation. The primary outcome was motility index (frequency × amplitude), and secondary outcomes included frequency, amplitude, and area under the curve.

RESULTS

Fifty-five experiments were conducted from samples obtained from 16 women. The mean motility index (√g·contractions/10 min) during the dose-response curve (oxytocin 10 to 10 M) in the control group was significantly greater than all the experimental groups; the mean estimated differences (95% confidence intervals) were -1.33 (-2.50 to -0.15, P = 0.02), -1.59 (-2.68 to -0.50, P = 0.004), and -1.88 (-2.97 to -0.80, P = 0.001) for the 30-, 60-, and 90-minute groups, respectively. When the experimental groups were compared, there were no significant differences in any of the contractility parameters; however, confidence intervals were wide.

CONCLUSIONS

Our study shows that oxytocin pretreatment attenuates oxytocin-induced contractility in human myometrium despite a rest period of up to 90 minutes after oxytocin administration. However, we were unable to determine whether increasing the rest period from 30 to 90 minutes results in improvement in myometrial contractility because of our small sample size relative to the variability in the contractile parameters. Further laboratory and clinical in vivo studies are necessary to determine whether a rest period up to 90 minutes results in improvement in myometrial contractility. In addition, further experimental studies are necessary to determine the key mechanisms of oxytocin receptor resensitization.

Breastfeeding or nipple stimulation for reducing postpartum haemorrhage in the third stage of labour

BACKGROUND

Oxytocin and prostaglandin are hormones responsible for uterine contraction during the third stage of labour. Receptors in the uterine muscles are stimulated by exogenous or endogenous oxytocin leading to uterine contractions. Nipple stimulation or breastfeeding are stimuli that can lead to the secretion of oxytocin and consequent uterine contractions. Consequently, uterine contractions can reduce bleeding during the third stage of labour.

OBJECTIVES

To investigate the effects of breastfeeding or nipple stimulation on postpartum haemorrhage (PPH) during the third stage of labour.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (15 July 2015) and reference lists of retrieved studies.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials comparing breast stimulation, breastfeeding or suckling for PPH in the third stage of labour were selected for this review.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion in terms of risk of bias and independently extracted data. Disagreements were resolved by a third review author.

MAIN RESULTS

We included four trials (4608 women), but only two studies contributed data to the review's analyses (n = 4472). The studies contributing data were assessed as of high risk of bias overall. One of these studies was cluster-randomised and conducted in a low-income country and the other study was carried out in a high-income country. All four included studies assessed blood loss in the third stage of labour. Birth attendants estimated blood loss in two trials. The third trial assessed the hematocrit level on the second day postpartum to determine the effect of the bleeding. The fourth study measured PPH ≥ 500 mL. Nipple stimulation versus no treatmentOne study (4385 women) compared the effect of suckling versus no treatment. Blood loss was not measured in 114 women (59 in control group and 55 in suckling group). After excluding twin pregnancies, stillbirths and neonatal deaths, the main analyses for this trial were performed on 4227 vaginal deliveries. In terms of maternal death or severe morbidity, one maternal death occurred in the suckling group due to retained placenta (risk ratio (RR) 3.03, 95% confidence interval (CI) 0.12 to 74.26; one study, participants = 4227; very low quality evidence); severe morbidity was not mentioned. Severe PPH (≥ 1000 mL) was not reported in this study.The incidence of PPH (≥ 500 mL) was similar in the suckling and no treatment groups (RR 0.95, 95% CI 0.77 to 1.16; one study, participants = 4227; moderate quality). There were no group differences between nipple stimulation and no treatment regarding blood loss in the third stage of labour (mean difference (MD) 2.00, 95% CI -7.39 to 11.39; one study, participants = 4227; low quality). The rates of retained placenta were similar (RR 1.01, 95% CI 0.14 to 7.16; one study, participants = 4227; very low quality evidence), as were perinatal deaths (RR 1.06, 95% CI 0.57 to 1.98; one study, participants = 4271; low quality), and maternal readmission to hospital (RR 1.01, 95% CI 0.14 to 7.16; one study, participants = 4227; very low quality). We downgraded the evidence for this comparison for risk of bias concerns in the one included trial (inappropriate analyses for cluster design) and for imprecision (wide CIs crossing the line of no difference and, for some outcomes, few events).Many maternal secondary outcomes (including side effects) were not reported. Similarly, most neonatal secondary outcomes were not reported. Nipple stimulation versus oxytocinAnother study compared the effect of nipple stimulation (via a breast pump) with oxytocin. Eighty-seven women were recruited but only 85 women were analysed. Severe PPH ≥ 1000 mL and maternal death or severe morbidity were not reported.There was no clear effect of nipple stimulation on blood loss (MD 15.00, 95% CI -24.50 to 54.50; one study, participants = 85; low quality evidence), or on postnatal anaemia compared to the oxytocin group (MD -0.40, 95% CI -2.22 to 1.42; one study, participants = 85; low quality evidence). We downgraded evidence for this comparison due to risk of bias concerns in the one included trial (alternate allocation) and for imprecision (wide CIs crossing the line of no difference and small sample size).Many maternal secondary outcomes (including side effects) were not reported, and none of this review's neonatal secondary outcomes were reported.

AUTHORS' CONCLUSIONS

None of the included studies reported one of this review's primary outcomes: severe PPH ≥ 1000 mL. Only one study reported on maternal death or severe morbidity. There were limited secondary outcome data for maternal outcomes and very few secondary outcome data for neonatal outcomes.There was no clear differences between nipple stimulation (suckling) versus no treatment in relation to maternal death, the incidence of PPH (≥ 500 mL), blood loss in the third stage of labour, retained placenta, perinatal deaths or maternal readmission to hospital. Whilst these data are based on a single study with a reasonable sample size, the quality of these data are mostly low or very low.There is insufficient evidence to evaluate the effect of nipple stimulation for reducing postpartum haemorrhage during the third stage of labour and more evidence from high-quality studies is needed. Further high-quality studies should recruit adequate sample sizes, assess the impact of nipple stimulation compared to uterotonic agents such as syntometrine and oxytocin, and report on important outcomes such as those listed in this review.

Stopping Oxytocin in Active Labor Rather Than Continuing it until Delivery: A Viable Option for the Induction of Labor

OBJECTIVE

Induction of labor (IOL), using intravenous oxytocin, is the artificial initiation of labor before its spontaneous onset for the purpose of delivery of the fetoplacental unit. Although there are various studies looking at dosages of oxytocin, only a few have addressed the issue of discontinuation of oxytocin in the active stage of labor. Thus, our study was conducted to evaluate the need for continuation versus discontinuation of oxytocin during active labor.

METHODS

This prospective, randomized controlled trial included 106 women who needed IOL. Oxytocin infusion was initiated at a rate of 3mIU/min and was incremental until 4-6cm cervical dilation. At this point the patients were randomly assigned into one of two groups. In group one, oxytocin was discontinued, and infusion was continued with 0.9% sodium chloride solution. In group two, oxytocin was continued at the same dose until delivery.

RESULTS

The duration of oxytocin infusion was 5.5 hours in the oxytocin discontinuation group and 11.0 hours in oxytocin continuation group (p<0.001). The total dose of oxytocin was significantly higher in group two (6.1 units vs. 16.5 units; p=<0.001). The induction-delivery interval was significantly less in group one (9.1 and 11.2 hours in group one and group two, respectively; p=0.023).

CONCLUSION

Oxytocin discontinuation in the active stage of labor did not prolong the active stage. The total duration of labor and total oxytocin dose were significantly less in the oxytocin discontinuation group. Our results suggest that oxytocin discontinuation is an alternative and viable option particularly in resource poor and economically challenged settings. It not only reduces the need for intense monitoring and prolonged oxytocin use-associated dangers but reduces the total cost of labor management.

Exposure to synthetic oxytocin during delivery and its effect on psychomotor development

The main objective is to examine the influence of oxytocin administration during delivery on psychomotor development at age five years. This was a retrospective cohort study involving two groups: children of mothers exposed vs. not exposed to oxytocin during labor. Of the 7,465 newborns registered in our maternity service during 2006 we randomly selected an initial sample of 400 children. Of these, 146 children were assessed using the motor scale of the Battelle Developmental Inventory. Other predictor variables that could potentially act as confounders and/or interact with the main relationship were also examined. The data were subjected to bivariate analysis, estimates of measures of strength of association, stratified analysis and multivariate binary logistic regression. The results indicate that exposure to synthetic oxytocin during delivery is an independent risk factor for a delay in gross and fine motor development. This was the case after controlling for the variables duration of labor and sex of the newborn, none of which modified the effect of oxytocin on gross and fine motor development. However, sex of the newborn were shown to be confounding gross motor development. In light of these results, and with the aim of preventing possible psychomotor alterations, further studies are now needed to analyze the effect that the oxytocin dose and the duration of perfusion may have on children's subsequent development.

Second-line uterotonics and the risk of hemorrhage-related morbidity

OBJECTIVE

Uterine atony is a leading cause of postpartum hemorrhage. Although most cases of postpartum hemorrhage respond to first-line therapy with uterine massage and oxytocin administration, second-line uterotonics including methylergonovine and carboprost are integral for the management of refractory uterine atony. Despite their ubiquitous use, it is uncertain whether the risk of hemorrhage-related morbidity differs in women exposed to methylergonovine or carboprost at cesarean delivery.

STUDY DESIGN

We performed a secondary analysis using the Maternal-Fetal Medicine Units Network Cesarean Registry. We identified women who underwent cesarean delivery and received either methylergonovine or carboprost for refractory uterine atony. The primary outcome was hemorrhage-related morbidity defined as intraoperative or postoperative red blood cell transfusion or the need for additional surgical interventions including uterine artery ligation, hypogastric artery ligation, or peripartum hysterectomy for atony. We compared the risk of hemorrhage-related morbidity in those exposed to methylergonovine vs carboprost. Propensity-score matching was used to account for potential confounders.

RESULTS

The study cohort comprised 1335 women; 870 (65.2%) women received methylergonovine and 465 (34.8%) women received carboprost. After accounting for potential confounders, the risk of hemorrhage-related morbidity was higher in the carboprost group than the methylergonovine group (relative risk, 1.7; 95% confidence interval, 1.2-2.6).

CONCLUSION

In this propensity score-matched analysis, methylergonovine was associated with reduced risk of hemorrhage-related morbidity during cesarean delivery compared to carboprost. Based on these results, methylergonovine may be a more effective second-line uterotonic.

Oxytocin: its mechanism of action and receptor signalling in the myometrium

Oxytocin is a nonapeptide hormone that has a central role in the regulation of parturition and lactation. In this review, we address oxytocin receptor (OTR) signalling and its role in the myometrium during pregnancy and in labour. The OTR belongs to the rhodopsin-type (Class 1) of the G-protein coupled receptor superfamily and is regulated by changes in receptor expression, receptor desensitisation and local changes in oxytocin concentration. Receptor activation triggers a number of signalling events to stimulate contraction, primarily by elevating intracellular calcium (Ca(2+) ). This includes inositol-tris-phosphate-mediated store calcium release, store-operated Ca(2+) entry and voltage-operated Ca(2+) entry. We discuss each mechanism in turn and also discuss Ca(2+) -independent mechanisms such as Ca(2+) sensitisation. Because oxytocin induces contraction in the myometrium, both the activation and the inhibition of its receptor have long been targets in the management of dysfunctional and preterm labours, respectively. We discuss current and novel OTR agonists and antagonists and their use and potential benefit in obstetric practice. In this regard, we highlight three clinical scenarios: dysfunctional labour, postpartum haemorrhage and preterm birth.

Effect of oxytocin discontinuation during the active phase of labor

OBJECTIVE

To observe the progression of labor when oxytocin use is limited to the onset of the active stage of labor.

METHODS

A randomized, prospective controlled study was performed to address the issue of oxytocin infusion after the onset of active labor in 140 patients. In the study group, infusion of oxytocin was discontinued at the onset of the active phase of labor, which was accepted as a cervical dilatation of 5 cm. In the control group, incremental oxytocin infusion was administered until 5 cm cervical dilatation, and then was maintained at the same level until delivery.

RESULTS

The primary outcome variable was duration from the beginning of the active phase to delivery. In the study group, the duration of the active phase of labor was about 30 min longer than in the control group and this difference was significant. The secondary outcomes of the study were maternal-fetal complications of oxytocin and in both groups there were no significant differences.

CONCLUSION

It is not reasonable to discontinue oxytocin infusion at the beginning of active labor. Nevertheless, for an accurate conclusion expanded investigations are needed.

Oxytocin administered during labor and breast-feeding: a retrospective cohort study

OBJECTIVE

The relationship between labor physiology and the onset of lactation leads to assess the potential correlation between oxytocin administration during labor and duration of breast-feeding.

METHODS

This study was designed as a retrospective cohort study where patients given synthetic oxytocin during labor induction were considered as the exposed cohort, and patients not given oxytocin formed the non-exposed cohort. Four hundred of the 7465 children born at our maternity during 2006 were randomly selected. Information about breast-feeding was available for 316 of these children. Eventual confounding or adjustment factors were analyzed using stratified and multivariate analysis.

RESULTS

Oxytocin was used for delivery of 189 (59.8%) newborns, multiplying the risk of bottle-feeding by 1.451 (95% CI 1.28-1.63). The best-fit regression model of oxytocin use effect on bottle-feeding included sex and gestational age of the newborn. The use of oxytocin also multiplies the risk of breast-feeding withdrawal at 3 months by 2.29 (95% CI 1.41-3.74). This effect is confounded by maternal age, being higher for mothers under 27 years.

CONCLUSION

Oxytocin administration during labor had some impact on both onset and duration of breast-feeding, particularly in mothers under 27 years of age and newborns delivered at term. Clinical Study registered at U.S.

NIH, ID

NCT01951040.

Oxytocin Pretreatment Attenuates Oxytocin-induced Contractions in Human Myometrium In Vitro

Background:

Oxytocin receptor desensitization has been shown to occur in humans at biomolecular level and in isolated rat myometrium; however, its effect on human myometrial contractility has not been demonstrated. The objective of this in vitro study was to investigate the contractile response of human pregnant myometrium to oxytocin after pretreatment with different concentrations of oxytocin for variable durations.

Methods:

Myometrial samples were obtained from 62 women undergoing elective cesarean deliveries under regional anesthesia. The strips were pretreated with oxytocin 10−10, 10−8, 10−5M, or physiological salt solution (control) for 2, 4, 6, or 12 h, followed by a dose–response testing with oxytocin 10−10 to 10−5M. Amplitude and frequency of contractions, motility index, and area under the curve during the dose–response period were recorded, analyzed with linear regression models, and compared among groups.

Results:

Pretreatment with oxytocin 10−5 and 10−8M significantly reduced motility index (estimate [standard error]: −0.771 [0.270] square root units, P = 0.005 and −0.697 [0.293], P = 0.02, respectively) and area under the curve (−3.947 [1.909], P = 0.04 and −4.241 [2.189], P = 0.05, respectively) compared with control group, whereas pretreatment with oxytocin 10−10M did not significantly attenuate contractions. Increase in duration of oxytocin pretreatment from 2 to 12 h significantly decreased amplitude (type 3 generalized estimating equation analysis: chi-square = 14.0; df = 3; P = 0.003), motility index (chi-square = 9.3; df = 3; P = 0.03), and area under the curve (chi-square = 10.5; df = 3; P = 0.02), but not the frequency of oxytocin-induced contractions.

Conclusion:

Pretreatment with oxytocin decreases oxytocin-induced myometrial contractions in a concentration and time-dependent manner, likely as a function of the oxytocin receptor desensitization phenomenon.

Effects of PGF2α on the expression of uterine activation proteins in pregnant human myometrial cells from upper and lower segment

CONTEXT

The lower and upper segments of the uterus may play different roles in the process of parturition. The switch from pregnancy to delivery involves changes in expression of uterine activation proteins (UAPs). Prostaglandin (PG) F2α has multiple and complex roles in the birth process in addition to its vital contractile role.

OBJECTIVE

The purpose of this study was to investigate whether PGF2α regulates the expression of UAPs in human myometrium and to compare PGF2α actions in lower and upper segments.

DESIGN

Cultured human myometrial cells from upper and lower segments were treated with PGF2α. Western blotting was used to determine the levels of connexin 43 (CX-43), prostaglandin endoperoxide synthase-2 (PTGS-2; cyclooxygenase-2), oxytocin receptor (OTR), and PGF2α receptor (PTGFR) in the cells. The small interfering RNA approach was used to knock down PTGFR.

RESULTS

PGF2α dose dependently increased CX-43 and PTGS-2 while decreasing PTGFR in upper and lower segments. PGF2α increased OTR in the lower segment while decreasing it in the upper segment. PGF2α lost its effects on PTGS-2 and OTR in PTGFR knockdown cells, but its effect on CX-43 remained. AL8810, a specific antagonist of PTGFR, reversed the actions of PGF2α on UAPs except for CX-43 in the lower segment. Indomethacin reversed the PGF2α-induced effects on CX-43 and PTGS-2, but it did not alter PGF2α-induced PTGFR and OTR expression. The stimulatory effects of PGF2α were enhanced in the presence of IL-1β, which reversed the inhibitory effect of PGF2α on PTGFR.

CONCLUSION

PGF2α regulates UAPs in both upper and lower segment cells through either direct or indirect pathways, indicating that PGF2α uniquely participates in uterine preparation for the onset of labor.

Oxytocin discontinuation during active labor in women who undergo labor induction

OBJECTIVE

The purpose of this study was to determine whether there is an increase in the cesarean delivery rate in women who undergo induction when oxytocin is discontinued in the active phase of labor.

STUDY DESIGN

We conducted a prospective randomized controlled trial of women who underwent induction of labor at term; they were assigned randomly to either routine oxytocin use (routine) or oxytocin discontinuation (DC) once in active labor. Analysis was by intention to treat.

RESULTS

Two hundred fifty-two patients were eligible for study analysis: 127 patients were assigned randomly to the routine group and 125 patients were assigned randomly to the DC group. Cesarean delivery rate was similar between the groups (routine, 25.2% [n = 32] vs the DC group, 19.2% [n = 24]; P = .25). There was a higher chorioamnionitis rate and slightly longer active phase in those women who were assigned to the DC group. In adjusted analysis, the rate of chorioamnionitis was not different by randomization group but was explained by the duration of membrane rupture and intrauterine pressure catheter placement.

CONCLUSION

Discontinuation of oxytocin in active labor after labor induction does not increase the cesarean delivery rate significantly.

Long chain polyunsaturated fatty acids alter oxytocin signaling and receptor density in cultured pregnant human myometrial smooth muscle cells

Epidemiological studies and interventional clinical trials indicate that consumption of long chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) such as docosahexaenoic acid (DHA) lengthen gestational duration. Although the mechanisms are not well understood, prostaglandins (PG) of the 2-series are known to play a role in the initiation and progress of labor. In animal studies, modest DHA provision has been shown to reduce placental and uterine PGE(2) and PGF(2α), matrix metalloproteinase (MMP)-2 and MMP-9 expression, and placental collagenase activity. However, modulation of PG biosynthesis may not account for all the effects of LC n-3 PUFAs in labor. We investigated one potential PG-independent mechanism of LC PUFA action using cultured pregnant human myometrial smooth muscle cells. Our goal was to characterize the effect of LC PUFA treatment on oxytocin signaling, a potent uterotonic hormone involved in labor. The addition of 10 µM-100 µM DHA or arachidonic acid (AA) to the culture media for 48 h resulted in dose dependent enrichment of these fatty acids in membrane lipid. DHA and AA significantly inhibited phosphatidylinositol turnover and [Ca(2+)](i) mobilization with oxytocin stimulation compared to bovine serum albumin control and equimolar oleic acid. DHA and AA significantly reduced oxytocin receptor membrane concentration without altering binding affinity or rate of receptor internalization. These findings demonstrate a role for LC n-3 PUFAs in regulation of oxytocin signaling and provide new insight into additional mechanisms pertaining to reports of dietary fish and fish oil consumption prolonging gestation.