Ask An Expert

A: Before actual labor, anything's possible. Generally speaking, women having their first baby will efface (thin out) their cervix first, then dilate closer to the time of labor. Women who have had babies already will tend to dilate first, but their cervix may still be thick until actual labor. During actual labor, there's a set scale that doctors and midwives use. It's called the Friedman Curve, wherin dilatation is tracked graphically against descent of the baby's presenting part (usually the head). In a first labor, dilatation should be about 1/2 to 1 cm. per hour. In a second or later labor, dilatation can proceed at about 1 1/2 or more cm. per hour. Descent of the fetal head should graph out as a line that crosses the line graphed for dilatation. You can find an example of the Friedman graph in any pregnancy book, but most experienced doctors and midwives do it in their heads during a labor.