Ans. B. Cervical dilatation > 3 cm. (Ref. Williams Obstetrics 22nd/ Ch. 17)CHARACTERISTICS OF NORMAL LABOR# The strict definition of labor-uterine contractions that bring about demonstrable effacement and dilatation of the cervix-docs not easily aid the clinician in determining when labor has actually begun, because this diagnosis is confirmed only retrospectively.# Several methods may be used to define its start - One quantifies onset as the clock time when painful contractions become regular. Unfortunately, uterine activity that causes discomfort, but that does not represent true labor, may develop at any time during pregnancy. A second method defines the onset of labor as beginning at the time of admission to the labor unit. Criteria at term require painful uterine contractions accompanied by one of the following:1) ruptured membranes,2) bloody "show",3) complete cervical effacement.FIRST STAGE OF LABOR - Friedman developed the concept of three functional divisions of labor:# Although the cervix dilates little during the preparatory division, the connective tissue components of the cervix change considerably. Sedation and conduction analgesia are capable of arresting this division of labor. The dilatational division, during which time dilatation proceeds at its most rapid rate, is unaffected by sedation or conduction analgesia. The pelvic division commences with the deceleration phase of cervical dilatation. The classical mechanisms of labor that involve the cardinal fetal movements of the cephalic presentation-engagement, flexion, descent, internal rotation, extension, and external rotation-take place principally during the pelvic division.- Two phases of cervical dilatation are defined.# The latent phase corresponds to the preparatory division and# The active phase to the dilatational division. Friedman subdivided the active phase into: the acceleration phase, the phase of maximum slope, and deceleration phase.Latent Phase:# The onset of latent labor, as defined by Friedman (1972), is the point at which the mother perceives regular contractions. The latent phase for most women ends at between 3 and 5 cm of dilatation.# Friedman and Sachtleben (1963) defined a prolonged latent phase as bein$ greater than 20 hours in the nullipara and 14 hours in the multipara. These are the 95th percentiles.# Factors that affect duration of the latent phase include:- excessive sedation or epidural analgesia;- unfavorable cervical condition, that is, thick, uneffaced, or undilated; and- false labor.Active Labor:# Cervical dilatation of 3 to 5 cm or more, in the presence of uterine contractions, can be taken to reliably represent the threshold for active labor.# Turning again to Friedman (1955), the mean duration of active-phase labor in nulliparas was 4.9 hours. Indeed, rates of cervical dilatation ranged from a minimum of 1.2 up to 6.8 cm/hr.# Friedman (1972) also found that multiparas progress somewhat faster in active-phase labor, with a minimum normal rate of 1.5 cm/hr.# Descent begins in the later stage of active dilatation, commencing at about 7 to 8 cm in nulliparas and becoming most rapid after 8 cm.# Active-labor phase abnormalities are quite common, reported in 25 percent of nulliparous and 15 percent of multigravidas.# Friedman (1972) subdivided active-phase problems into protraction and arrest disorders.- He defined protraction as a slow rate of cervical dilatation or descent, which for nulliparas was less than 1.2 cm dilatation per hour or less than 1 cm descent per hour. For multiparas, protraction was defined as less than 1.5 cm dilatation per hour or less than 2 cm descent per hour. He defined arrest as a complete cessation of dilatation or descent.- Arrest of dilatation was defined as 2 hours with no cervical change, and arrest of descent as 1 hour without fetal descentSECOND STAGE OF LABOR# This stage begins when cervical dilatation is complete and ends with fetal delivery.# The median duration is about 50 minutes for nulliparas and about 20 minutes for multiparas.DURATION OF LABOR# It is reported that the mean length of first- and second-stage labor was approximately 9 hours in nulliparous women without regional analgesia, and that the 95th percentile upper limit was 18.5 hours. Corresponding times for multiparous women were a mean of about 6 hours with a 95th percentile maximum of 13.5 hours.