The graph below portrays a labor curve for a woman, gravida 3, para 2, at 39 weeks' gestation. Membranes were ruptured at 4 cm. The fluid was clear and there has been no indication of fetal distress. Previous infants weighed 3500 g and 3750 g. The estimated weight of this infant, which appears normal on ultrasound, is 3200 g. This labor curve is compatible with which of the following conditions?

Ans. D. Secondary arrest of dilationThe labor portrayed in this labor curve is characteristic of a secondary arrest of dilation. The woman has entered the active phase of labor, as she previously progressed from 2 to 6cm in less than 2h. The multiparous woman normally progresses at a rate of at least 1.5cm/h (and the nullipara at least 1.2cm/h) in the active phase. Dilation at a slower rate is a protraction disorder. Primary dysfunction, prolonged latent phase, and hypertonic dysfunction occur prior to the active phase. The best evidence available indicates that this labor is hypotonic. Since the ultrasound indicates a fetus without obvious abnormalities, and since the patient's previous infants were larger than this one, we assume the absence of cephalopelvic disproportion (CPD). Oxytocin is the treatment of choice. If CPD were suspected, then the treatment preferred by many obstetricians would be cesarean section.