During labor mother and fetus are evaluated at intervals to assess their well-being and determine how the labor is progressing. These assessments require skillful physical diagnosis and the ability to translate the acquired information into meaningful prognostic decision-making. We describe a coordinated approach to the assessment of labor. Graphing of serial measurements of cervical dilatation and fetal station creates \"labor curves,\" which provide diagnostic and prognostic information. Based on these curves we recognize nine discrete labor abnormalities. Many may be related to insufficient or disordered contractile mechanisms. Several factors are strongly associated with development of labor disorders, including cephalopelvic disproportion, excess analgesia, fetal malpositions, intrauterine infection, and maternal obesity. Clinical cephalopelvimetry involves assessing pelvic traits and predicting their effects on labor. These observations must be integrated with information derived from the labor curves. Exogenous oxytocin is widely used. It has a high therapeutic index, but is easily misused. Oxytocin treatment should be restricted to situations in which its potential benefits clearly outweigh its risks. This requires there be a documented labor dysfunction or a legitimate medical reason to shorten the labor. Normal labor and delivery pose little risk to a healthy fetus; but dysfunctional labors, especially if stimulated excessively by oxytocin or terminated by complex operative vaginal delivery, have the potential for considerable harm. Conscientiously implemented, the approach to the evaluation of labor outlined in this review will result in a reasonable cesarean rate and minimize risks that may accrue from the labor and delivery process.

The ongoing debate about what models of cervical dilatation and fetal descent should guide clinical decision-making has sown uncertainty among obstetric practitioners. We previously argued that the adoption of recently published labor assessment guidelines promoted by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine may have been premature. Before accepting any new clinical approaches as the standard of care, their underlying hypotheses should be thoroughly tested to ensure they are at least equivalent (or, preferably, superior) to existing management paradigms. Some of the apparent urgency to subscribe to new clinical tactics has been fueled by legitimate concerns about the rise in the cesarean delivery rate over the past several decades. A major contributor to this change in practice patterns is that more cesarean deliveries are being done for diagnoses that fall under the rubric of dystocia than ever before. As a consequence, traditional labor curves-fundamental for assessing labor progress-and the practice paradigms associated with them have received intense scrutiny as a possible contributor to this delivery trend. Moreover, the recent proposal of new labor curves and accompanying management guidelines has, understandably, fed the appetite to correct a perceived problem. However, the cesarean delivery rate rose most rapidly during decades when there was no major change in traditional labor curves or in the guidelines for their interpretation. Also, during the years since the new guidelines were first published, there has been no major fall in cesarean delivery frequency. This raises the question of whether there was truly a fundamental flaw in the traditional labor management paradigms or whether their proper interpretation and use had been somehow forgotten, ignored, or corrupted. More important, existing studies have shown that application of the new guidelines often (but not always) results in a modest fall in the cesarean delivery rate, but that this change may be accompanied by significant increases in maternal and neonatal morbidity. These results strongly suggest more caution in the adoption of the American College of Obstetricians and Gynecologists / Society for Maternal-Fetal Medicine labor assessment recommendations. They are based on a hypothesis that has yet to undergo thorough evaluation of its risks and benefits.

The measurement of cervical dilation of a pregnant woman is used to monitor the progression of labor until 10 cm when pushing begins. There is anecdotal evidence that labor tracks across repeated pregnancies; moreover, no statistical methodology has been developed to address this important issue, which can help obstetricians make more informed clinical decisions about an individual woman\'s progression. Motivated by the NICHD Consecutive Pregnancies Study (CPS), we propose new methodology for analyzing labor curves across consecutive pregnancies. Our focus is both on studying the correlation between repeated labor curves on the same woman and on using the cervical dilation data from prior pregnancies to predict subsequent labor curves. We propose a hierarchical random effects model with a random change point that characterizes repeated labor curves within and between women to address these issues. We employ Bayesian methodology for parameter estimation and prediction. Model diagnostics to examine the appropriateness of the hierarchical random effects structure for characterizing the dependence structure across consecutive pregnancies are also proposed. The methodology was used in analyzing the CPS data and in developing a predictor for labor progression that can be used in clinical practice.

In the 1930s, investigators in the US, Germany and Switzerland made the first attempts to quantify the course of labor in a clinically meaningful way. They emphasized the rupture of membranes as a pivotal event governing labor progress. Attention was also placed on the total number of contractions as a guide to normality. Beginning in the 1950s, Friedman determined that changes in cervical dilatation and fetal station over time were the most useful parameters for the assessment of labor progress. He showed all normal labors had similar patterns of dilatation and descent, differing only in the durations and slopes of their component parts. These observations led to the formulation of criteria that elevated the assessment of labor from a rather arbitrary exercise to one guided by scientific objectivity. Researchers worldwide confirmed the basic nature of labor curves and validated their functionality. This system allows us to quantify the effects of parity, analgesia, maternal obesity, prior cesarean, maternal age, and fetal presentation and position on labor. It permits analysis of outcomes associated with labor aberrations, quantifies the effectiveness of treatments and assesses the need for cesarean delivery. Also, dysfunctional labor patterns serve as indicators of short- and long-term risks to offspring. We still lack the necessary translational research to link the physiologic manifestations of uterine contractility with changes in dilatation and descent. Recent efforts to interpret electrohysterographic patterns hold promise in this regard, as does preliminary exploration into the molecular basis of dysfunctional labor. For now, the clinician is best served by a system of labor assessment proposed more than 60 years ago and embellished upon in considerable detail since.

OBJECTIVE: Maternal weight is thought to impact labor. With rising rates of obesity and inductions, we sought to evaluate labor times among induced women by body mass index (BMI) category.
METHODS: Retrospective cohort study of term inductions from 2005 to 2010. BMI categories were: normal weight (NW), overweight (OW), and obese (Ob) (18.5-24.9, 25-29.9, ≥30 kg/m(2)). Kruskal-Wallis tests compared median latent labor (LL) length and active labor (AL) length. Chi-square determined associations. Multivariable logistic regression controlled for confounders. Analyses were stratified by parity.
RESULTS: A total of 448 inductions were analyzed. For nulliparas, there was no difference in LL by BMI category (p = 0.22). However, OW nulliparas had a longer AL compared to NW and Ob nulliparas (3.2, 1.7, 2.0 h, p = 0.005). For multiparas, NW had the shortest LL (5.5 h, p = 0.025) with no difference in AL among BMI categories (p = 0.42). The overall cesarean rate was 23% with no difference by BMI category (p = 0.95). However, Ob women had a greater percentage of first stage cesareans (41%) and NW had a greater percentage of second stage cesareans (55%), p = 0.06.
CONCLUSIONS: The association between BMI and labor length among inductions differs by phase of labor and parity. BMI also influences the stage of labor in which a cesarean occurs.

OBJECTIVE: To compare labor progression in twin vs singleton gestations.
METHODS: Retrospective review of electronic database created by Consortium on Safe Labor, reflecting labor and delivery information from 12 clinical centers 2002-2008. Women with twin gestations, cephalic presentation of presenting twin, gestational age ≥34 weeks, with ≥2 cervical examinations were included. Exclusion criteria were fetal anomalies or demise. Singleton controls were selected by the same criteria. Categorical variables were analyzed by χ(2); continuous by Student t test. Interval censored regression was used to determine distribution for time of cervical dilation in centimeters, or \"traverse times,\" and controlled for confounding factors. Repeated-measures analysis constructed mean labor curves by parity and number of fetuses.
RESULTS: A total of 891 twin gestations were compared with 100,513 singleton controls. Twin gestations were more often older, white or African American, earlier gestational age, increased prepregnancy body mass index, and with lower birthweight. There was no difference in number of prior cesarean deliveries, induction, or augmentation, or epidural use. Median traverse times increased at every centimeter interval in nulliparous twins, in both unadjusted and adjusted analysis (P < .01). A similar pattern was noted for multiparas in both analyses. Labor curves demonstrated a delayed inflection point in the labor pattern for nulliparous and multiparous twin gestations.
CONCLUSIONS: Both nulliparous and multiparous women have slower progression of active phase labor with twins even when controlling for confounding factors.