637 4060 ADDRESS: 60 Mount Street Lower, Grand Canal Dock, Dublin 2 info@merrionultrasound.ie

What is a dilation?

What Is Dilation FAQs

What is dilation?

In normal conditions and during most part of your pregnancy, your cervix, the opening of your uterus, remains closed and tight. That is a good thing because its job is to keep your baby inside of you. At the end of gestation and during labour, the cervix begins to develop some changes to allow the baby to come out. One of these changes (and the most important one) is dilation. Dilation happens when your cervix begins to open up.

How much dilation does the cervix needs?

For your baby to be born, your cervix will need to have 10 cms. of dilation. This is approximately the diameter of a softball or a small bagel, or in obstetric terminology, approximately the size of your baby´s head.

Does dilation have phases?

You can say it has, but really it is the labour stage that has them. Dilation happens during the first stage of labour, which has 3 phases:

1. The early labour phase, which begins with the first real contractions and ends when the cervix reaches the 3 cms. of dilation,

2. The active labour phase, in which the contractions get more intense, continues the dilation from 3 to 7 cms.

3. The transition phase, which goes from 7 to 10 cms. of dilation. Obviously, this can vary from woman to woman.

In how much time does dilation reach 10 centimetres?

It depends on each woman. Medically speaking, in primiparous women, there is a rule that indicates that for every cms. dilated, 1 hour has to pass, reaching easily the 10 to 12 hours of labour. In multiparous women, this time is reduced to half.

What happens if I cannot dilate?

This can happen to many women due to a vast number of reasons: wrong pelvic shape, baby´s position, stress, induction happening prematurely, etc. Your physician will try expecting management, giving your cervix chance to dilate, or will apply active management (if appropriate), using synthetic substances to help your cervix. If none of these results, you will need to have a cC-section.


Nuchal Translucency

12-14 weeks


Anatomy Survey

21-22 weeks


Later Dating

10-17 weeks


Gender Scan

19 weeks onwards


Growth & Well Being

22 weeks onwards


Post Dates & Liquor

40 weeks onwards


What Our Patients Say

Gráinne Macken

This is my second visit to Merrion Fetal, I was very pleased on both occasions. Lovely quiet waiting room, appointment was on time. The 20-week scan is very detailed we enjoyed watching our baby on the large TV screen. We got some beautiful photos. The nurse was very pleasant and talked us through all the measurements and anatomy. I would highly recommend this scanning clinic.”

Áine Gibney

I had the best experience at the Merrion Fetal Health clinic for my 20-week big scan. The staff were so friendly and so nice and the lovely lady who did my ultrasound scan was amazing. She was so thoroughgoing to absolutely everything and gave me such reassurance on how my baby was growing and developing. I would recommend any Mother to be to attend here if you are looking for a comfortable, reassuring and super pleasant experience.”

Linda O'Sullivan

Highly recommend! We had an early scan due to a little scare at the start of pregnancy and then another at 12 weeks to make sure all was good again. Helen who was scanning on both days was fantastic. We felt totally relaxed and un-rushed while she took her time finding the best angle of baby to get us the clearest pictures as keepsakes all while making sure everything was perfect with baby. She reassured us throughout and I can honestly say it was the best money we ever spent getting both scans done.

Please let Helen know we are 18 weeks now and flying along Highly recommend!



About The Clinic

Merrion Fetal Health Pregnancy Scans Dublin 2

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Dr. Rhona Mahony

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Pregnancy scans lead sonographer at Merrion Fetal Health

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All articles on the blog and website are intended as information only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team.


This website was formerly Merrion Fetal Health. The clinic has undergone a rebrand and is now known as Merrion Ultrasound.