When late-pregnancy cervical checks begin, many expectant parents seek a precise answer regarding the onset of labor. These checks assess how the body is progressing toward childbirth, focusing on the physical changes of the cervix. Receiving a measurement like 70% effaced often sparks intense anticipation, yet this number is only one piece of a highly variable biological puzzle. Understanding effacement and how it interacts with other metrics is necessary to manage expectations about when labor will actually begin.
Understanding Cervical Effacement
Effacement describes the process where the cervix, the lower part of the uterus, softens, shortens, and thins out in preparation for delivery. Throughout most of pregnancy, the cervix is firm, long, and closed, typically measuring between three and five centimeters. Effacement is measured using a percentage scale, ranging from 0% to 100%.
A measurement of 0% indicates the cervix is still thick and long, while 100% means the cervix is completely thinned out. Being 70% effaced means the cervix has completed nearly three-quarters of its thinning process. This change occurs because of hormonal shifts and the pressure of the baby’s head dropping deeper into the pelvis.
Why Effacement Alone Doesn’t Predict Labor Timing
Despite the progress indicated by 70% effacement, this measurement offers no reliable timeline for when active labor will start. Effacement is considered a pre-labor change, meaning it can occur hours, days, or even weeks before regular contractions begin.
The speed of progression is highly individualized and varies greatly between people and pregnancies. For a first-time mother, the cervix often effaces significantly before it begins to dilate. Progression from 70% to 100% effacement can happen gradually over a long period or extremely quickly once true labor begins. A single cervical check only provides a snapshot of the current status, not a prediction of the future.
The Three Labor Metrics
To form a complete picture of labor readiness and progression, healthcare providers assess three interconnected measurements during a cervical examination. Effacement is only one component; the other two are dilation and station. All three measurements must be considered together because they describe different, yet simultaneous, physical changes.
Dilation
Dilation refers to the opening of the cervix, measured in centimeters. Throughout most of pregnancy, the cervix is closed, or 0 centimeters dilated. For a vaginal delivery to occur, the cervix must open completely to 10 centimeters, the point of full dilation. This widening occurs as uterine contractions pull the thinned-out cervix up and over the baby’s head.
Station
Station describes the baby’s position within the birth canal relative to the mother’s pelvis. It measures the baby’s presenting part, usually the head, against the ischial spines—two bony points in the pelvis. The station is measured using a number scale that ranges from negative to positive.
A zero station means the baby’s head is level with the ischial spines, indicating the head is “engaged.” Negative numbers, such as -3 or -2, mean the baby is still high above the spines. Positive numbers, like +1 or +2, indicate the baby has descended past the spines and is very low in the birth canal. The progression of the station is important for determining the effectiveness of contractions and the likelihood of a successful vaginal delivery.
Identifying the Onset of Active Labor
Focusing on physical sensations provides a more reliable indication of labor onset than any single cervical measurement. The transition from latent labor, where effacement and early dilation occur, to active labor is marked by a noticeable change in contraction patterns. True labor contractions become progressively longer, stronger, and closer together, unlike the irregular contractions of early or false labor.
In active labor, contractions typically occur every two to five minutes, lasting 45 to 60 seconds each, and their intensity makes it difficult to talk through them. Other physical signs that suggest labor is progressing include the rupture of the amniotic membranes (water breaking) or the appearance of a bloody show. Guidance is to contact a healthcare provider when contractions are consistently five minutes apart, lasting for one minute, and following this pattern for at least one hour.