During the last weeks of pregnancy, the cervix narrows and thins, known as cervical effacement, which can be checked by an obstetrician through a physical exam or ultrasound. The progress of cervical effacement is measured as a percentage, and cervical dilation is another sign of impending labor. A woman cannot give birth until she is fully dilated at 10 centimeters. Doctors use the Bishop Score to assess a woman’s readiness for delivery.
Towards the end of a woman’s pregnancy, the fetus begins to drop and the cervix begins to narrow and thin. This is known as cervical deletion and usually begins during the last few weeks of pregnancy. An obstetrician can check for a thinning of the cervix during a physical exam or with an ultrasound machine. As the cervix narrows and the opening dilates, the mucus plug in the cervical opening is usually also expelled.
The cervix is the lower part of the uterus and is joined to the vagina. Normally, the cervix is narrower than the rest of the uterus and has very thick walls. It is usually 1 to 3 inches (3 to 5 centimeters) long and tightly closed early in a healthy pregnancy.
During the last month of a normal pregnancy, the fetus usually begins to descend lower in the uterus. During this time, the hormones will cause the walls of the cervix to soften. This fetal repositioning usually also triggers the onset of cervical effacement, which could also be referred to as maturation or thinning.
Cervical effacement and dilation might begin a few weeks before labor begins in some women. In others, however, it may not start until hours before labor. An obstetrician or midwife will usually check a pregnant woman’s cervix regularly during the last few weeks of pregnancy. This can be done in some cases with an ultrasound machine, but the cervix can also be checked during a physical exam.
The progress of cervical obliteration is usually measured as a percentage. If the cervix has not thinned at all, it is considered 0% effaced. When the cervical walls are about half their normal size, they are considered 50% effaced.
It is only when the first stage labor contractions begin that cervical elimination will be complete. By this time, the walls of the cervix will have shortened considerably. Once cervical elimination is 100%, the walls of the cervix fuse completely with the rest of the uterus.
Cervical dilatation is another sign of impending labor. As the cervical obliteration progresses, the entrance to the cervix begins to open. Doctors typically check how dilated a woman’s cervix is by inserting a finger into her vagina and feeling the cervix. Dilation is usually measured in centimeters, but some doctors may measure it in “fingers,” since a fingertip is about 1 centimeter (0.4 inch) wide. The mucus plug within the cervical opening, known as a bloody spectacle, will usually exit the body as dilation occurs.
A woman cannot successfully give birth until she is fully dilated, meaning her cervical opening is 10 centimeters (about 4 inches) wide. If your cervix is not dilated and thinned by 40 weeks of pregnancy, doctors will often consider inducing labor. By assessing how effaced and dilated a woman’s cervix is, as well as the position of the fetus, doctors can rate her with something called the Bishop Score. Generally, the lower a woman’s Bishop score, the more likely she is to be induced, or that the baby may even need to be delivered via C-section.
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