Effacement: what it means when your cervix is 50% or 100% effaced

Effacement is the thinning and shortening of your cervix, the neck of the womb, as your body gets ready for birth. It is written as a percentage. Cleveland Clinic says 0% effaced means the cervix is still long and firm, and 100% means it is completely thinned. You need to be fully effaced and 10cm dilated before you push. You cannot feel it happen; a vaginal examination shows it.

What the percentage on your notes means

Mayo Clinic says the cervix is usually 3.5 to 4cm long before labour, and that at 0% effacement it is still at least 2cm long. As it softens and thins, the number climbs. Cleveland Clinic gives a simple way to read it: 80% effaced means you are 80% of the way through thinning, with 20% to go. At 100% the cervix cannot get any thinner.

Cleveland Clinic explains the cause. As your baby drops into the pelvis, a head-down baby presses on the cervix, and labour contractions add more pressure. Over time the cervix goes from hard and long to soft and short. Your gynae may start checking it at full term, around 39 weeks.

Effacement and dilation, first baby or not

Effacement is the cervix thinning; dilation is it opening. They usually happen together, but the order can differ. Cleveland Clinic says that with a first baby the cervix will probably thin before it opens, while in a second or third pregnancy it is more common to be dilated but not effaced.

HealthHub describes the change in the latent phase of labour: the cervix thins out and becomes soft and stretchable while it opens to about 3cm. An NHS trust leaflet from Northern Lincolnshire and Goole says this flattening is what effacement means, and that the latent phase can last several days or weeks before active labour.

Can you feel your cervix thinning?

No. Cleveland Clinic says you cannot feel effacement, and only your healthcare provider can tell whether it has started. You may notice other signs that labour is near: losing your mucus plug, feeling your baby drop, pelvic pressure or more vaginal discharge. Mayo Clinic says that while the cervix starts to change you might feel mild contractions that come and go, or nothing at all.

Practice tightenings do not do the job. Cleveland Clinic says Braxton Hicks contractions will not make your cervix change or efface.

Effacement and induction of labour

Effacement matters most when labour needs a push. ACOG says doctors may use the Bishop score, a rating from 0 to 13 for the condition of the cervix, to judge readiness, and a score under 6 means the cervix may not be ready. KKH says your doctor does a vaginal examination to assess the cervix before choosing a method of induction of labour, and some methods, such as a prostaglandin pessary, are used to soften it.

Thinning too early is a different problem. Cleveland Clinic says a cervix that effaces too soon can lead to labour before 37 weeks, and it asks you to tell your provider early about any symptoms that worry you. Our stages of labour guide shows where effacement fits in.

Frequently asked questions

Can you be effaced but not dilated?

Yes. Cleveland Clinic says it is likely with a first baby, when the cervix often thins before it opens.

How long does effacement take?

Nobody can say for you. Cleveland Clinic says some women are 2cm dilated and 30% effaced for weeks, while others stay at 0% until a few days before delivery.

What does 100% effaced mean?

Your cervix has thinned completely. Cleveland Clinic says it must be 100% effaced, and 10cm dilated, before the pushing stage of a vaginal birth can begin.

Does effacement mean labour is starting?

It means labour is near or under way, Cleveland Clinic says, but no one can predict exactly how long you have before you are ready to push.

Related terms

• Dilation: How far your cervix has opened in labour, measured in centimetres from closed to 10cm.
• Contractions: The tightening and relaxing of your womb that opens the cervix and pushes your baby down in labour.
• Induction of Labour: Starting labour with medical help, such as a pessary, balloon or drip, instead of waiting for it to begin.
• Braxton Hicks Contractions: Irregular, usually painless tightenings of the womb before labour. They do not open the cervix or mean labour has started.

See every term in the glossary