Toward the end of your pregnancy, your doctor will examine your cervix for signs of dilation or widening. The cervix, a narrow neck-like passage of fibromuscular tissue, connects the main body of the uterus to the vagina or birth canal. For your baby to be born, the cervix must be fully dilated. When your baby is close to full term, hormones known as prostaglandins help start and regulate that process.
In the last weeks of your pregnancy, a visit to the doctor’s office may confirm that your cervix is already dilated by a few centimeters. While this indicates that it’s time to pack your hospital labor bag with a few essentials, it does not mean you need to head off to the hospital. Dilation is a gradual process. Although every birth experience is different, it can take hours, days or even weeks, to dilate a few centimeters.
If your cervix is dilated a few centimeters, that means you are in the latent or early phase of labor. It means that your cervix is thinning in preparation for birth but the baby’s head is not yet engaged in the pelvis. In this phase of labor, contractions may begin to occur every three to five minutes. They may continue consistently or stop and start.
When dilation is measured between four and seven centimeters, a woman is considered to be in active labor. This active phase usually lasts around five hours in first time mothers and two hours in mothers who have already given birth, but again every labor is different.
During pregnancy the cervix helps support the baby, but as contractions proceed that support lessens until finally the baby’s head can pass through the dilated cervix into the birth canal.
As the cervix becomes wider, it also becomes shorter. Other names for the process are ripening or effacement.
Dilation of between seven and 10 centimeters means a woman has entered the transition phase of labor. In this phase contractions are stronger, more frequent and reliably regular. For many women, this is the most difficult part of labor. The urge to push may be there but it’s too soon to act on it.
By the time women reach 10 centimeters of dilation, the baby is in position and ready to be born. This is the shortest phase of labor.
While you don’t exactly feel your cervix dilating, there is one noticeable sign your cervix is getting ready for labor. That sign is the loss of the mucus plug that seals off the cervix and is designed to prevent bacteria from entering the uterus and harming the baby.
As your cervix dilates, this viscous plug becomes loose and is eventually discharged, signalling that labor will probably start within a few days. For some the mucus plug will be tinged with pink, red or brown blood and that’s why it is also called a bloody show. This is perfectly normal. However, any indication of red blood is not normal. Spotting with bright red blood during any phase of pregnancy or early labor is always cause for concern and should be reported to your doctor since it could indicate a problem with the placenta.
Doctors measure the amount of time it takes the cervix to dilate when considering whether to induce labor, use forceps during the delivery, or deliver the baby by Cesarean section. When labor does not seem to be progressing according to schedule, doctors may apply a gel or vaginal insert of synthesized prostaglandin to the cervix to help the dilation process along.
In rare cases, the cervix dilates and thins too soon in a pregnancy, potentially leading to miscarriage or preterm labor. This is known as cervical incompetence and it can be treated by a procedure that prevents the cervix from completely dilating. Cervical incompetence is rare but if you experience any of the following symptoms, always contact your doctor:
- Vaginal bleeding at any time in your pregnancy
- Mucous discharge before 36 weeks
- Pelvic pressure or cramping before 36 weeks
- Intense lower back pain
In the weeks following childbirth your cervix will naturally narrow and thicken again, although it may not become as narrow as it was before childbirth.