Which of the following is a sign of true labor?

Progressive cervical dilation is a hallmark of true labor. In true labor, the contractions become increasingly regular, intense, and frequent, leading to significant changes in the cervix. This means that as labor progresses, the cervix undergoes effacement and dilation, moving from its closed state to becoming thinner and wider, facilitating the passage of the baby through the birth canal.

This characteristic distinguishes true labor from false labor, where contractions may be irregular or lack intensity and do not lead to any significant cervical changes. The idea is that in true labor, the body is preparing for delivery, and the progressive nature of cervical dilation reflects this preparation.

The other options illustrate characteristics that do not typically indicate true labor. Irregular contractions do not result in progressive dilation, and decreased cervical dilation contradicts the essential feature of advancement seen in true labor. Constant contraction intensity is also not a characteristic seen in progressive labor, as true labor contractions usually vary in intensity and duration.