Normal cervical dilatation pattern in late pregnancy and labor

The mean cervical changes of the last 4 weeks of pregnancy (prelabor) and during labor have been calculated. In prelabor, the cervix dilates at an accelerating rate. In the final days of prelabor, the mean dilatation for the nullipara is 1.8cm., and 2.2cm. for the multipara. Effacement progresses steadily in late pregnancy; at term, the nullipara’s cervix is 70 per cent effaced, and that of the multipara 61 per cent. The “cervical coefficient” (the product of dilatation times per cent effacement) at any point in prelabor is relatively constant for all parities. Normal active labor performed under optimal conditions is characterized by: (1) constant acceleration in dilatation without any terminal “deceleration phase,” (2) brevity, and (3) dilatation at approximately the same rate for nulliparas and multiparas after 4cm. has been reached.