The total cesarean rate in the United States in 2006 was 466% greater than in 1970 (31.1% and 5.5%, respectively). Among term, low-risk, nulliparous women, a cesarean rate of 25% was reported by the Centers for Disease Control and Prevention in 2005. These rates are higher than ever before and farther from national objectives. While in some cases necessary for the health of the mother and/or neonate, cesareans are major surgical procedures that carry multiple short- and long-term risks. It is suggested that a cesarean rate between 5-10% for any world region seems to achieve the best outcomes, whereas a rate higher than 15% seems to result in more harm than good. Studying factors that may contribute to cesareans must be a research priority.
Dystocia (i.e., slow, abnormal progression of labor) is the most common indication for cesareans. Clinically, dystocia is generally defined as a delay in cervical dilation progression beyond which accelerative interventions, e.g., uterine contraction augmentation via oxytocin administration, are considered justifiable. Rates of augmentation in contemporary practice suggest that the clinical expectations of nulliparous labor have surpassed normalcy. Hence, it is possible that current definitions of dystocia, in terms of cervical dilation rates, may be inappropriately defined. The first manuscript of this dissertation document presents a systematic review aimed at identifying the norms and limits of active phase labor length and active phase cervical dilation rates in low-risk, nulliparous women with spontaneous labor onset in order to better define labor expectations. It is concluded that active phase labor is longer and has a wider range of normal than is generally appreciated. Likewise, overall linear rates of cervical dilation in the active phase are not as steeply sloped as traditionally believed.
Although the cause(s) of true labor dystocia can rarely be diagnosed with objective certainty, the greatest contributor is inefficient uterine contractions, a diagnosis lacking stringent criteria and with unknown cause(s). Physiological factors potentially contributing to inefficient uterine contractions via a uterine fatigue pathway and eventually culminating in longer labor durations is the focus of the second and third manuscripts. These prospective works studied term, low-risk, nulliparous women with a labor care provider diagnosis of spontaneous labor in the early active-phase (n = 93).
The second manuscript reports the relationships between labor duration and maternal oxygenation, hydration, energy substrate availability, pain, and anxiety as well as reporting group differences on these measures. Measures were made at the diagnosis of active phase labor onset (baseline) and baseline + 4 hours. The third manuscript investigates lactate dehydrogenase (LDH) as a potential, retrospective indicator of uterine preparedness for labor. Maternal serum LDH samples were collected upon a provider diagnosis of active phase labor onset and 24-30 hours post-vaginal delivery. Paired-sample differences are described as are the relationships between total LDH and isoenzyme levels and several outcome variables. In addition to the main study findings, these data also reinforce that many women, based on a priori definitions, are misclassified as being in active labor based on subsequent rates of cervical dilation.