The second stage of labor.

The second stage of labor extends from complete cervical dilatation to delivery. During this stage, descent and rotation of the presenting part occur as the fetus passively negotiates its passage through the birth canal. Generally, descent begins during the deceleration phase of dilatation as the cervix is drawn upward around the fetal presenting part. The most common means of assessing the normality of the second stage of labor is to measure its duration, but progress can be more meaningfully gauged by measuring the change in fetal station as a function of time. Accurate clinical identification and evaluation of differences in patterns of fetal descent are necessary to assess second stage of labor progress and to make reasoned judgments about the need for intervention. Three distinct graphic abnormalities of the second stage of labor can be identified: protracted descent, arrest of descent, and failure of descent. All abnormalities have a strong association with cephalopelvic disproportion but may also occur in the presence of maternal obesity, uterine infection, excessive sedation, and fetal malpositions. Interpretation of the progress of fetal descent must be made in the context of other clinically discernable events and observations. These include fetal size, position, attitude, and degree of cranial molding and related evaluations of pelvic architecture and capacity to accommodate the fetus, uterine contractility, and fetal well-being. Oxytocin infusion can often resolve an arrest or failure of descent or a protracted descent caused by an inhibitory factor, such as a dense neuraxial block. It should be used only if thorough assessment of fetopelvic relationships reveals a low probability of cephalopelvic disproportion. The value of forced Valsalva pushing, fundal pressure, and routine episiotomy has been questioned. They should be used selectively and where indicated.

Neonatal head circumference to maternal mid-transverse pelvic distance ratio as a key anatomical predictor for dystocia: Retrospective case-control study.

OBJECTIVE: This study aimed to examine maternal and neonatal factors in cesarean deliveries due to dystocia, including cephalopelvic disproportion, latent-phase prolongation, and fetal malposition or malpresentation. Additionally, we sought to compare the differences between the dystocia subgroups. METHOD AND MATERIALS: This retrospective case-control study included women who delivered between January 2010 and June 2021 after 37 weeks of pregnancy and underwent abdominal-pelvic CT scans within 5 years before and after delivery. Neonatal factors were extracted from medical charts immediately after delivery. RESULTS: Among the 292 women studied, those with cesarean deliveries for dystocia were older (mean ± SD, 34.2 ± 4.27 vs. 32.2 ± 3.8, p-value = 0.002), had higher pre-pregnancy BMI (22.7 ± 3.67 vs. 21.4 ± 3.48, p-value = 0.012) and term-BMI (27.4 ± 3.72 vs. 25.9 ± 3.66, p-value = 0.010), shorter interspinous distance (ISD, the distance between ischial spine) (10.8 ± 0.76 vs. 11.2 ± 0.85 cm, p-value = 0.003), and longer head circumference (HC) (35 ± 1.47 vs. 34.4 ± 1.36 cm, p-value = 0.003) compared to those who had vaginal deliveries. Univariate logistic regression for dystocia revealed associations between HC/maternal height and HC/ISD ratios (OR, 2.02 [95% confidence interval, CI, 1.4 ~ 2.92], 12.13 [3.2 ~ 46.04], respectively). Multivariate logistic analysis indicated that maternal age, ISD, and HC were significant factors for dystocia (OR, 1.11 [95% CI, 1.01 ~ 1.21], 0.49 [0.26 ~ 0.91], 1.53 [1.07 ~ 2.19], respectively). The subgroup with latent-phase prolongation exhibited the lowest birthweight/term-BMI ratio (124 ± 18.8 vs. 113 ± 10.3 vs. 134 ± 19.1, p-value = 0.013). CONCLUSION: The HC/ISD ratio emerged as a crucial predictor of dystocia, suggesting that reducing term-BMI could potentially mitigate latent-phase prolongation. Further research assessing the maternal mid-pelvis during pregnancy and labor is warranted, along with efforts to reduce BMI during pregnancy.

The active phase of labor.

The active phase of labor begins at various degrees of dilatation when the rate of dilatation transitions from the relatively flat slope of the latent phase to a more rapid slope. No diagnostic manifestations demarcate its onset, other than accelerating dilatation. It ends with apparent slowing of dilatation, a deceleration phase, which is usually short in duration and frequently undetected. Several aberrant labor patterns can be detected during the active phase, including protracted dilatation, arrest of dilatation, prolonged deceleration phase and failure of descent. Underlying factors may include cephalopelvic disproportion, excessive neuraxial block, poor uterine contractility, fetal malpositions, malpresentations, uterine infection, maternal obesity, advanced maternal age and previous cesarean delivery. When an active-phase disorder is identified, cesarean delivery is justifiable if there is compelling clinical evidence of disproportion. A prolonged deceleration disorder is strongly associated with disproportion and second stage abnormalities. Shoulder dystocia may occur if vaginal delivery eventuates. This review discusses several issues raised by the introduction of new clinical practice guidelines for labor management.

Covariation of fetal skull and maternal pelvis during the perinatal period in rhesus macaques and evolution of childbirth in primates.

A large brain combined with an upright posture in humans has resulted in a high cephalopelvic proportion and frequently obstructed labor. Fischer and Mitteroecker [B. Fischer, P. Mitteroecker, Proc. Natl. Acad. Sci. U.S.A. 112, 5655-5660 (2015)] proposed that the morphological covariations between the skull and pelvis could have evolved to ameliorate obstructed labor in humans. The availability of quantitative data of such covariation, especially of the fetal skull and maternal pelvis, however, is still scarce. Here, we present direct evidence of morphological covariations between the skull and pelvis using actual mother-fetus dyads during the perinatal period of Macaca mulatta, a species that exhibits cephalopelvic proportions comparable to modern humans. We analyzed the covariation of the three-dimensional morphology of the fetal skull and maternal pelvis using computed tomography-based models. The covariation was mostly observed at the pelvic locations related to the birth canal, and the forms of the birth canal and fetal skull covary in such a way that reduces obstetric difficulties. Therefore, cephalopelvic covariation could have evolved not only in humans, but also in other primate taxa in parallel, or it could have evolved already in the early catarrhines.

Head circumference, as predictor of cephalopelvic disproportion: A prospective analysis of cases of spontaneous vaginal delivery and caesarean section in Ekiti State, Nigeria.

Cephalopelvic disproportion (CPD) is a previously undiagnosed anatomical misfit between maternal pelvis and the fetal head. It is one of the major indications for cesarean section (CS), especially in sub-Saharan Africa. Early diagnosis, could avert events that can increase maternal and perinatal morbidity and mortality associated with this condition. This study was designed to determine the mean head circumference of the fetus in relation to CPD as an indicator for caesarean section. A total of 350 parturients who had spontaneous vaginal deliveries (group A) were compared with another 350 parturients who had cephalopelvic disproportion leading to CS (group B). The socio-demographic characteristics, delivery parameters, head circumference, fetal weight and length were recorded in a proforma and analyzed using SPSS version 21. P value was set at 0.05. The mean head circumference for the all the babies delivered in this study was 34.6 ±1.7cm. The mean head circumference of babies delivered to women with CPD via caeserean section compared to those who had vaginal delivery was significantly greater (35.15±1.5 vs 34.1±1.8, mean difference 1.9±0.1, X2,0.308 p <0.001). The cut-off for diagnosis of cephalopelvic disproportion was head circumference 34.8cm which has a specificity of about 74% and sensitivity of 88% with area under the curve being 66%. The study demonstrated that when the head circumference of a baby is 34.8cm and above, the risk of having cephalopelvic disproportion leading to a CS is high with sensitivity of 88% and specificity of about 74%.

Magnetic Resonance Imaging-Based Nomogram to Antenatal Predict Cesarean Delivery for Cephalopelvic Disproportion in Primiparous Women.

BACKGROUND: Cephalopelvic disproportion (CPD)-related obstructed labor is associated with maternal and neonatal morbidity and mortality. Accurate prediction of whether a primiparous woman is at high risk of an unplanned cesarean delivery would be a major advance in obstetrics. PURPOSE: To develop and validate a predictive model assessing the risk of cesarean delivery in primiparous women based on MRI findings. STUDY TYPE: Prospective. POPULATION: A total of 150 primiparous women with clinical findings suggestive of CPD. FIELD STRENGTH/SEQUENCE: T1-weighted fast spin-echo sequences, single-shot fast spin-echo (SSFSE) T2-weighted sequences at 1.5 T. ASSESSMENT: Pelvimetry and fetal biometry were assessed independently by two radiologists. A nomogram model combined that the clinical and MRI characteristics was constructed. STATISTICAL TESTS: Univariable and multivariable logistic regression analyses were applied to select independent variables. Receiver operating characteristic (ROC) analysis was performed, and the discrimination of the model was assessed by the area under the curve (AUC). Calibration was assessed by calibration plots. Decision curve analysis was applied to evaluate the net clinical benefit. A P value below 0.05 was considered to be statistically significant. RESULTS: In multivariable modeling, the maternal body mass index (BMI) before delivery, bilateral femoral head distance, obstetric conjugate, fetal head circumference, and fetal abdominal circumference was significantly associated with the likelihood of cesarean delivery. The discrimination calculated as the AUC was 0.838 (95% confidence interval [CI]: 0.774-0.902). The sensitivity and specificity of the nomogram model were 0.787 and 0.764, and the positive predictive and negative predictive values were 0.696 and 0.840, respectively. The model demonstrated satisfactory calibration (calibration slope = 0.945). Moreover, the decision curve analysis proved the superior net benefit of the model compared with each factor included. DATA CONCLUSION: Our study might provide a nomogram model that could identify primiparous women at risk of cesarean delivery caused by CPD based on MRI measurements. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Magnetic resonance imaging in late pregnancy to improve labour and delivery outcomes - a systematic literature review.

BACKGROUND: Magnetic resonance imaging (MRI) provides excellent soft tissue visualisation which may be useful in late pregnancy to predict labour outcome and maternal/neonatal birth trauma. OBJECTIVE: To study if MRI in late pregnancy can predict maternal and neonatal outcomes of labour and birth. METHODS: Systematic review of studies that performed MRI in late pregnancy or immediately postpartum. Studies were included if they imaged maternal pelvic or neonatal structures and assessed birth outcome. Meta-analysis was not performed due to the heterogeneity of studies. RESULTS: Eighteen studies were selected. Twelve studies explored the value of MRI pelvimetry measurement and its utility to predict cephalopelvic disproportion (CPD) and vaginal breech birth. Four explored cervical imaging in predicting time interval to birth. Two imaged women in active labour and assessed mouldability of the fetal skull. No marker of CPD had both high sensitivity and specificity for predicting labour outcome. The fetal pelvic index yielded sensitivities between 59 and 60%, and specificities between 34 to 64%. Similarly, although the sensitivity of the cephalopelvic disproportion index in predicting labour outcome was high (85%), specificity was only 56%. In women with breech presentation, MRI was demonstrated to reduce the rates of emergency caesarean section from 35 to 19%, and allowed better selection of vaginal breech birth. Live birth studies showed that the fetal head undergoes a substantial degree of moulding and deformation during cephalic vaginal birth, which is not considered during pelvimetry. There are conflicting studies on the role of MRI in cervical imaging and predicting time interval to birth. CONCLUSION: MRI is a promising imaging modality to assess aspects of CPD, yet no current marker of CPD accurately predicts labour outcome. With advances in MRI, it is hoped that novel methods can be developed to better identify individuals at risk of obstructed or pathological labour. Its role in exploring fetal head moulding as a marker of CPD should be further explored.

Pelvic and neonatal size correlations in light of evolutionary hypotheses.

OBJECTIVE: This study aimed to analyze the correlations between maternal size, neonatal size, and gestational variables. METHODS: Our sample comprises 131 mother-infant dyads. We investigated correlations between five neonatal traits (gestational age, birthweight, head, suboccipito-brematic, and abdominal girths), three maternal traits (height, BMI, and uterus height), and three pelvic variables (conjugate, inter-spinous diameters, and sub-pubic angle) using computed tomography pelvimetry. RESULTS: We found that the five neonatal traits were significantly intercorrelated. BMI was not correlated with neonatal traits while maternal height was correlated with birthweight, suboccipito-brematic, and abdominal girth. In the multiple regression models, gestational age was correlated with birthweight, head, and abdominal girth. Among the neonatal and pelvimetry correlations, conjugate diameter was slightly correlated with suboccipito-bregmatic girth, but inter-spinous and sub-pubic angle were not correlated with neonatal traits. Uterus height predicted all neonatal variables, but it was not correlated with gestational age. DISCUSSION: Our results suggest that fetal growth is shaped by maternal phenotype rather than external ecological factors. The association of the inlet size with suboccipito-bregmatic girth reflects the tight fit between the neonatal brain and the maternal pelvis dimensions, an adaptation that would reduce the risk of cephalo-pelvic disproportion, while the absence of tight fit at the midplane and outlet could be due to the effect of the pelvic relaxation. Uterus distention is not the only mechanism involved in the initiation of parturition. Birth and pregnancy are complex processes and we suggest that maternal-neonatal associations are the result of a combination of multiple obstetric tradeoffs.

Antepartum evaluation of the obstetric conjugate at transabdominal 2D ultrasound: A feasibility study.

INTRODUCTION: The obstetric conjugate represents the shortest anteroposterior diameter of the birth canal and it reflects the capacity of the pelvic inlet to allow the passage and the engagement of the fetal head. The antepartum evaluation of this parameter may be attempted at digital examination to predict the risk of cephalopelvic disproportion, but the accuracy of clinical pelvimetry is notoriously poor. The aim of our study was to describe the sonographic measurement of the obstetric conjugate at transabdominal 2D-ultrasound and to assess its reproducibility. MATERIAL AND METHODS: This is a prospective cohort study conducted at a tertiary University hospital. A non-consecutive series of pregnant women with uncomplicated singleton pregnancies attending the antenatal clinic for routine booking from 34 weeks of gestation onward were included. The ultrasound probe was longitudinally placed above the level of the symphysis and the interpubic fibrocartilaginous disk was visualized. Then the promontory was identified as the most prominent segment of the sacral vertebral column. The obstetric conjugate was measured as the distance between the inner edge of the interpubic disk and the promontory. The inter- and intraobserver repeatability of this measurement was calculated using the intraclass correlation coefficient (ICC) and the Bland-Altman method. RESULTS: In all, 119 women were considered eligible for the study; of these, 111/119 (93.3%) women were included in the analysis with a median gestational age of 36.0 (35.0-37.0) weeks. The mean obstetric conjugate measurement was 11.4 ± 0.93 mm for the first operator and 11.4 ± 0.91 mm for the second operator. The overall interobserver ICC was 0.95 (95% [confidence interval] CI 0.92-0.96) and the overall intraobserver ICC was 0.97 (95% CI 0.96-0.98). Limits of agreement ranged from -0.84 to 0.80 for interobserver measures and from -0.64 to 0.62 for intraobserver measures. The degree of reliability was also analyzed for women with a body mass index ≥30 and for women with a gestational age ≥37 weeks. The inter- and intraobserver ICCs were respectively 0.97 (95% CI 0.90-0.98) and 0.98 (0.95-0.99) in the former group and 0.96 (95% CI 0.93-0.98) and 0.97 (95% CI 0.95-0.98) in the latter group. CONCLUSIONS: Our study demonstrated that among pregnant women at term gestation, sonographic measurement of the obstetric conjugate is feasible and reproducible.

Cephalopelvic disproportion as primary diagnosis for cesarean section: Role of neonatal birthweight in relation to maternal height at a Hospital in Merida, Mexico.

OBJECTIVE: To analyze the association between newborn and maternal characteristics and the risk for cesarean section (CS) due to cephalopelvic disproportion (CPD) and non-CPD causes compared to vaginal deliveries (VD) in a sample of infants and mothers from Merida, Yucatan, Mexico. METHODS: The final sample consisted of 3453 single, live, and term infants born between January 2016 and May 2017 at the Maternal-Infant Hospital in Merida and their mothers (aged ≥19 years). The mode of delivery was established as the dependent variables: (a) VD, (b) CS due to CPD, and (c) non-CPD CS. Independent variables were maternal height and weight, the number of previous VD, newborn weight, and neonatal birthweight (BW) index/maternal height index. A multinomial regression model was used to analyze the association between newborn and maternal characteristics and outcome variable. RESULTS: By mode of delivery, 2124 (62%) births corresponded to VD, 1042 (30%) to non-CPDCS, and 287 (8%) to CS due to CPD. Mothers who had CS due to CPD weighed more at the end of their pregnancy and were shorter. Maternal age and weight increased the risk for having CS due to CPD compared to VD and maternal height, and the number of previous VD reduces the risk for experiencing CS due to CPD compared to vaginal births. The relative risk ratio for higher neonatal BW/maternal height index was significant for CS due to CPD and non-CPD CS. CONCLUSION: According to our results from a public hospital in Merida, Mexico, CPD is a result of the interrelation of maternal and fetal size, rather than an independent result of maternal height or BW.

Incidence, causes, and maternofetal outcomes of obstructed labor in Ethiopia: systematic review and meta-analysis.

BACKGROUND: Obstructed labor is a preventable obstetric complication. However, it is an important cause of maternal mortality and morbidity and of adverse outcomes for newborns in resource-limited countries in which undernutrition is common resulting in a small pelvis in which there is no easy access to functioning health facilities with a capacity to carry out operative deliveries. Therefore, this systematic review and meta-analysis aimed to estimate the incidence, causes, and maternofetal outcomes of obstructed labor among mothers who gave birth in Ethiopia. METHOD: for this review, we used the standard PRISMA checklist guideline. Different online databases were used for the review: PubMed, Google Scholar, EMBASE, Cochrane Library, HINARI, AFRO Library Databases, and African Online Journals. Based on the adapted PICO principles, different search terms were applied to achieve and access the essential articles. The search included all published and unpublished observational studies written only in the English language and conducted in Ethiopia. Microsoft Excel 16 was used for data entrance, and Stata version 11.0 (Stata Corporation, College Station, Texas, USA) was used for data analysis. RESULTS: I included sixteen (16) primary studies with twenty-eight thousand five hundred ninety-one (28,591) mothers who gave birth in Ethiopia. The pooled incidence of obstructed labor in Ethiopia was 12.93% (95% CI: 10.44-15.42, I2 = 98.0%, p < 0.001). Out of these, 67.3% (95% CI: 33.32-101.28) did not have antenatal care follow-up, 77.86% (95% CI: 63.07-92.66) were from the rural area, and 58.52% (95% CI: 35.73- 82.31) were referred from health centers and visited hospitals after 12 h of labor. The major causes of obstructed labor were cephalo-pelvic disproportion 64.65% (95% CI: 57.15- 72.14), and malpresentation and malposition in 27.24% (95% CI: 22.05-32.42) of the cases. The commonest complications were sepsis in 38.59% (95% CI: 25.49-51.68), stillbirth in 38.08% (95% CI: 29.55-46.61), postpartum hemorrhage in 33.54% (95% CI:12.06- 55.02), uterine rupture in 29.84% (95% CI: 21.09-38.58), and maternal death in 17.27% (95% CI: 13.47-48.02) of mothers who gave birth in Ethiopia. CONCLUSION: This systematic review and meta-analysis showed that the incidence of obstructed labor was high in Ethiopia. Not having antenatal care follow-up, rural residency, and visiting hospitals after 12 h of labor increased the incidence of obstructed labor. The major causes of obstructed labor were cephalo-pelvic disproportion, and malpresentation and malpresentation. Additionally, the commonest complications were sepsis, stillbirth, postpartum hemorrhage, uterine rupture, and maternal death. Thus, promoting antenatal care service utilization, a good referral system, and availing comprehensive obstetric care in nearby health institutions are recommended to prevent the incidence of obstructed labor and its complications.

The Relation between Head Circumference and Mid-Pelvic Circumference: A Simple Index for Cephalopelvic Disproportion Evaluation.

INTRODUCTION: Cephalopelvic disproportion (CPD) is one of the most common obstetric complications. Since CPD is the disproportion between the fetal head and maternal bony pelvis, evaluation of the head circumference (HC) relative to the maternal bony pelvis may be a useful adjunct to pre-labor CPD evaluation. The aim of the present study was a proof-of-concept evaluation of the ratio between HC and pelvic circumference (PC) as a predictor of CPD. METHODS: Of 11,822 deliveries, 104 cases that underwent an abdominopelvic CT for any medical indication and who underwent normal vaginal deliveries (NVDs) (n = 84) or cesarean deliveries (CD) due to CPD (n = 20) were included retrospectively. Maternal pelvis dimensions were reconstructed and neonatal HC, as a proxy for fetal HC, was measured. The correlation between cases of CPD and cephalopelvic circumference index (CPCI), which represents the ratio between the HC and PC in percentage (HC/PC × 100), was evaluated. RESULTS: The mid-pelvis CPCI (MP-CPCI) was larger in CD groups as compared to the NVD group: 103 ± 11 versus 97 ± 8%, respectively (p = 0.0003). In logistic regression analysis, the MP-CPCI was found to be independently associated with CD due to CPD: each 1% increase in MP-CPCI increased the likelihood of CD for CPD by 11% (adjusted odds ratio [aOR] 1.11, 95% CI, 1.03-1.19, p = 0.004). The aOR for CD due to CPD increased incrementally as the MP-CPCI increased, from 3.56 (95% CI, 1.01-12.6) at MP-CPCI of 100 to 5.6 (95% CI, 1.63-19.45) at 105, 21.44 (95% CI, 3.05-150.84) at 110, and 28.88 (95% CI, 2.3-362.27) at MP-CPCI of 115. CONCLUSIONS: The MP-CPCI, representing the relative dimensions of the fetal HC and maternal PC, is a simple tool that can potentially distinguish between parturients at lower and higher risk of CPD. Prospective randomized studies are required to evaluate the feasibility of prenatal pelvimetry and MP-CPCI to predict the risk of CPD during labor.

Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma.

Without cesarean delivery, obstructed labor can result in maternal and fetal injuries or even death given a disproportion in size between the fetus and the maternal birth canal. The precise frequency of obstructed labor is difficult to estimate because of the widespread use of cesarean delivery for indications other than proven cephalopelvic disproportion, but it has been estimated that at least 1 million mothers per year are affected by this disorder worldwide. Why is the fit between the fetus and the maternal pelvis so tight? Why did evolution not lead to a greater safety margin, as in other primates? Here we review current research and suggest new hypotheses on the evolution of human childbirth and pelvic morphology. In 1960, Washburn suggested that this obstetrical dilemma arose because the human pelvis is an evolutionary compromise between two functions, bipedal gait and childbirth. However, recent biomechanical and kinematic studies indicate that pelvic width does not considerably affect the efficiency of bipedal gait and thus is unlikely to have constrained the evolution of a wider birth canal. Instead, bipedalism may have primarily constrained the flexibility of the pubic symphysis during pregnancy, which opens much wider in most mammals with large fetuses than in humans. We argue that the birth canal is mainly constrained by the trade-off between 2 pregnancy-related functions: while a narrow pelvis is disadvantageous for childbirth, it offers better support for the weight exerted by the viscera and the large human fetus during the long gestation period. We discuss the implications of this hypothesis for understanding pelvic floor dysfunction. Furthermore, we propose that selection for a narrow pelvis has also acted in males because of the role of pelvic floor musculature in erectile function. Finally, we review the cliff-edge model of obstetric selection to explain why evolution cannot completely eliminate cephalopelvic disproportion. This model also predicts that the regular application of life-saving cesarean delivery has evolutionarily increased rates of cephalopelvic disproportion already. We address how evolutionary models contribute to understanding and decision making in obstetrics and gynecology as well as in devising health care policies.

"New or not-so-new" labor management practices and cesarean delivery for arrest of progress.

BACKGROUND: Because nearly one-third of births in the United States are now achieved by cesarean delivery, comprising more than 1.27 million women each year, national organizations have recently published revised guidelines for the management of labor. These new guidelines stipulate that labor arrest should not be diagnosed unless ≥6 cm cervical dilatation has been reached or labor has been stimulated for at ≥6 hours. OBJECTIVE: To determine the cervical dilatation and hours of labor stimulation prior to cesarean delivery for arrest of dilatation. MATERIALS AND METHODS: Between January 1, 1999, andDecember 31, 2000, a prospective observational study of all primary cesarean deliveries was conducted at 13 university centers comprising the Eunice Kennedy Shriver National Institute for Child Health and Human Development, Maternal-Fetal Medicine Units Network. This secondary analysis includes all live-born, singleton, nonanomalous, cephalic gestations delivered by primary cesarean delivery at ≥37 weeks. A cesarean delivery was considered to have been performed for arrest of dilatation if the indication for the procedure was failure to progress, cephalopelvic disproportion, or failed induction. Augmentation was defined as stimulation after spontaneous labor had been previously diagnosed. Analysis included both the latent and active phases of labor. The active phase of labor was diagnosed when cervical dilatation was ≥4 cm in the presence of uterine contractions. RESULTS: A total of 13,269 primary cesarean deliveries were available for analysis, 8,546 (65%) of which were performed for inadequate progress of labor with cervical dilatation recorded at the time of cesarean delivery. Of these cesarean deliveries for labor arrest, a total of 719 (8%) were performed in the latent phase of labor and 7827 (92%) were performed when cervical dilatation was ≥4 cm (active phase). Approximately two-thirds (n = =5876; 69%) received intrauterine pressure monitoring. A total of 5636 women (66% of those reaching the active phase of labor) had reached ≥6 cm cervical dilatation before cesarean delivery was performed. Moreover, 7440 (95%) of the 7827 women in active labor had ≥6 cm dilatation or had received labor stimulation ≥6 hours prior to cesarean delivery for arrest of dilatation. CONCLUSION: Women undergoing primary cesarean delivery for arrest of dilatation 15 years before the recommendations of the Obstetrics Care Consensus had received bona fide efforts to achieve adequate labor consistent with the recommendations of the Consensus. Because 95% of these women had ≥6 cm dilatation or had received labor stimulation ≥6 hours prior to cesarean delivery for arrest of dilatation, these new recommendations are unlikely to change the cesarean delivery rates.

Cliff-edge model predicts intergenerational predisposition to dystocia and Caesarean delivery.

Recently, we presented the cliff-edge model to explain the evolutionary persistence of relatively high incidences of fetopelvic disproportion (FPD) in human childbirth. According to this model, the regular application of Caesarean sections since the mid-20th century has triggered an evolutionary increase of fetal size relative to the dimensions of the maternal birth canal, which, in turn, has inflated incidences of FPD. While this prediction is difficult to test in epidemiological data on Caesarean sections, the model also implies that women born by Caesarean because of FPD are more likely to develop FPD in their own childbirth compared with women born vaginally. Multigenerational epidemiological studies indeed evidence such an intergenerational predisposition to surgical delivery. When confined to anatomical indications, these studies report risks for Caesarean up to twice as high for women born by Caesarean compared with women born vaginally. These findings provide independent support for our model, which we show here predicts that the risk of FPD for mothers born by Caesarean because of FPD is 2.8 times the risk for mothers born vaginally. The congruence between these data and our prediction lends support to the cliff-edge model of obstetric selection and its underlying assumptions, despite the genetic and anatomical idealizations involved.

Differences in rate and medical indication of caesarean section between Germany and Japan.

BACKGROUND: There are growing concerns about the increasing rate of caesarean section (CS) worldwide. Various strategies have been implemented to reduce the proportion of CS to a reasonable level. Most research on medical indications for CS focuses on nationwide evaluations. Comparative research between different countries is sparse. The aim of this study was to evaluate differences in the rate and indications for CS between Japan and Germany in 2012 and 2013. METHODS: Comparison of the overall rate and medical indications for CS in two cohort studies from Germany and Japan. We used data from the German Perinatal Survey and the Japan Environment and Children's Study (JECS). RESULTS: We analyzed data of 1 335 150 participants from the German perinatal survey and of 62 533 participants from JECS and found significant differences between the two countries in CS rate (30.6% vs 20.6%) and main medical indications: cephalopelvic disproportion (3.2% vs 1.3%; OR: 2.4 [95% CI: 2.2-2.6]), fetal distress (7.3% vs 2.3%; OR: 3.4 [95%-CI: 3.2-3.6]), and past uterine surgery/repeat CS (8.4% vs 8.8%; OR: 0.9 [95%-CI: 0.9-1]). CONCLUSION: There are differences in the rate and medical indications for CS between Germany and Japan at the population level. Fetal distress was identified as a medical indication for CS more often Germany than in Japan. Considering the substantial diagnostic uncertainty of electronic fetal monitoring (EFM) as the major indicator for fetal distress, it would seem to be reasonable to rethink CS decision algorithms.

[Development of CT Pelvimetry Using Deep Learning Based Reconstruction].

PURPOSE: X-ray pelvimetry is typically performed for the diagnosis of the cephalopelvic disproportion (CPD). The purpose of this study was to assess the utility of new computed tomography (CT) reconstruction "deep learning based reconstruction (DLR) " in ultra-low dose CT pelvimetry. METHOD: CT pelvimetry was performed 320-row CT. All CT images were reconstructed with and without DLR and transferred for workstation to processing martius and guthmann view. Radiologist and obstetrician-gynecologist subjectively ranked overall image quality of each CT image from the best to the worst. Exposure dose of the CT pelvimetry used a following calculated value, displayed CT dose index (CTDI) vol multiplied by measured value using the thimble chamber and pelvic phantom, and of the X-ray pelvimetry used Japan-Diagnositic Refernce Levels 2015 as a reference, were compared. RESULT: 3D images obtained from CT pelvimetry with DLR showed accurate biparietal diameter and obstetric conjugate as compared to without DLR. Radiation dose of CT pelvimetry is 0.39 mGy, of X-ray pelvimetry is 1.18 mGy, respectively. Conculusion: Although the visualizing high contrast object, such as bone morphology, is likely to reduce exposure dose in CT examination generally, DLR enable to further dose reduction to keep image quality. 3D image processing from CT pelvimetry solves the problem of expansion rate in X-P pelvimetry and provide accurate measurements. Furthermore, CT pelvimetry can undergo more comfortable position for Pregnant Woman in Labor.

Cliff-edge model of obstetric selection in humans.

The strikingly high incidence of obstructed labor due to the disproportion of fetal size and the mother's pelvic dimensions has puzzled evolutionary scientists for decades. Here we propose that these high rates are a direct consequence of the distinct characteristics of human obstetric selection. Neonatal size relative to the birth-relevant maternal dimensions is highly variable and positively associated with reproductive success until it reaches a critical value, beyond which natural delivery becomes impossible. As a consequence, the symmetric phenotype distribution cannot match the highly asymmetric, cliff-edged fitness distribution well: The optimal phenotype distribution that maximizes population mean fitness entails a fraction of individuals falling beyond the "fitness edge" (i.e., those with fetopelvic disproportion). Using a simple mathematical model, we show that weak directional selection for a large neonate, a narrow pelvic canal, or both is sufficient to account for the considerable incidence of fetopelvic disproportion. Based on this model, we predict that the regular use of Caesarean sections throughout the last decades has led to an evolutionary increase of fetopelvic disproportion rates by 10 to 20%.

There Is No "Obstetrical Dilemma": Towards a Braver Medicine with Fewer Childbirth Interventions.

Humans give birth to big-brained babies through a bony birth canal that metamorphosed during the evolution of bipedalism; they have a tighter fit at birth between baby and bony birth canal than do our closest relatives the chimpanzees; and they are incapable of grasping onto caregivers as early as infant chimpanzees develop the skill. Since the mid-20th century, these observations and more have been linked together into the "obstetrical dilemma" (OD): human babies are helpless because they are born early to escape before they outgrow the mother's pelvis, the expansion of which is prevented by natural selection for bipedalism. The OD continues to be a popular idea, often expressed as incontrovertible fact, but it no longer deserves its popularity. There are better explanations for gestation length, childbirth difficulty, and the developmental biology of newborns than mainly or only because of natural selection's constraints on women's hips. And humans are not born early either, as is widely assumed. This all-too-powerful human evolutionary narrative deserves our skeptical consideration. Bias from OD thinking is likely amplifying the perceived risk of cephalopelvic and fetopelvic disproportion during labor-contributing, even if slightly, to medicine's underestimation of women's bodies and over-implementation of childbirth interventions.

Study on the cephalopelvic relationship with cephalic presentation in nulliparous full-term Chinese pregnant women by MRI with three-dimensional reconstruction.

PURPOSE: To analyze the relationship between fetal head size and maternal pelvis size using magnetic resonance imaging (MRI) with a 3-D reconstruction technique. METHODS: A total of 301 nulliparous full-term Chinese pregnant women with cephalic presentation were enrolled and received MRI examinations before labor onset. Data were collected and imported into Mimics software to reconstruct the maternal pelvis and fetus. RESULTS: Of 301 pregnant women, 212 underwent vaginal delivery and 32 received cesarean section. The body mass index (BMI) was significantly different between the vaginal delivery group and the suspected cephalopelvic disproportion (CPD) group; the larger the BMI, the higher was the risk of CPD. The transverse diameter of the pelvic inlet and the posterior sagittal diameter of the midpelvis were significantly larger in the vaginal delivery group, compared with the suspected CPD group. Fetal weight > 3.5 kg could be used as a diagnostic indicator for CPD. CONCLUSIONS: BMI is a risk factor for CPD, and fetal weight < 3.5 kg is an important diagnostic indicator for natural delivery in Chinese pregnant women.