Cervical check: the three numbers

When a clinician performs a cervical exam, they're gathering three numbers: dilation (how open), effacement (how thin), and station (how low baby is sitting). Together they help answer questions like "is labor established?", "how is baby positioned?", or "how likely is an induction to work today?" Any single number in isolation tells you very little — the three together are the picture.

Headline to hold onto: effacement tends to take longer, and dilation can change quickly. A low dilation number with strong effacement is genuine progress, not a setback.

Dilation is how open the cervix is, measured in centimeters. It starts closed and stretches to about 10 cm — "complete" — which is the diameter needed for baby's head to pass through. In early labor, dilation is usually slow. Once labor is established and the cervix is well-effaced, dilation can move quickly — sometimes several centimeters in a short stretch. That's why an early "only 2 cm" number is not a verdict on how the rest of labor will go.

Each circle shows the approximate cervical opening at that centimeter. Full dilation (10 cm) is when the cervix is out of baby's way.

Effacement is how thin and short the cervix has become. Before labor, the cervix is a firm tube roughly 3–4 cm long. As prep work happens — over weeks in late pregnancy and hours in early labor — the tissue softens, shortens, and eventually pulls up into the lower uterine segment. 0% is a long, thick cervix. 100% is paper-thin. Most of this remodeling is quiet, invisible work.

Effacement usually takes longer than dilation, especially for first-time labors — the cervix generally has to thin substantially before it can open efficiently. Someone who is "1 cm and 90% effaced" often has more prep work done than someone who is "3 cm and 30% effaced."

Station describes where the presenting part of baby (usually the head) sits in your pelvis, measured against the ischial spines — two bony landmarks in the mid-pelvis. Station 0 means baby's head is right at the spines, which is considered engaged. Negative numbers are above the spines (higher up); positive numbers are below (descending toward crowning at +3).

Station is about descent, not opening. Baby can move down between exams even when dilation feels stuck — and vice versa.

The three numbers make sense in combination. Two examples with very different meanings:

• 1 cm · 80% effaced · station −2

  Cervix is barely open but almost fully thinned. Baby is high but the prep work is well underway. Once labor is truly established, dilation often catches up quickly.

• 4 cm · 40% effaced · station 0

  Cervix is more open but still fairly thick. Baby is engaged, which is often good news for descent. The remaining effacement work is what the next stretch of labor is likely to focus on.

Neither snapshot predicts the whole labor. Bodies don't dilate on a schedule, and a single number — high or low — isn't a promise.

• ·ACOG Committee Opinion 766: Approaches to Limit Intervention During Labor and Birth↗ — ACOG
• ·Intrapartum care for a positive childbirth experience (2018)↗ — World Health Organization
• ·Evidence on: Vaginal Exams During Labor↗ — Evidence Based Birth
• ·Fetal station, engagement, and cardinal movements↗ — Spinning Babies®

Plain-language paraphrase of the sources above. Educational only — not a substitute for your care team's judgment about your specific situation.