What Does Dilation Mean in Pregnancy?
Every woman's pregnancy journey is unique, but for most first-time mothers, waiting hours to give birth is a common experience.
"You aren't very dilated yet, so we're in for a bit of a wait," is a frequent statement to many people in labor for the first time. The word "dilation" may mean "something wider," but here's how it applies to the labor and delivery room.
What does dilation mean? The clinical definition
Dilation (sometimes spelled as dilatation) is a stage of the labor process when the cervix opens to allow the passage of an infant through the birth canal, according to the American Pregnancy Association.
In the first stage of labor, the cervix simultaneously softens and thins out, or effacement, as it opens when the infant pushes against it. During stage 2, the laboring person enters the pushing stage, or when the cervix is fully opened and dilated to a width of about 10 centimeters.
How quickly a birthing mother will achieve full dilation depends on several factors, according to 2023 report, and includes the following factors:
- Parity, or whether or not she has previously been pregnant or given birth
- Medical history
- Pelvic anatomy
- Size and position of the baby as labor begins
Dilation can go slowly for first-time mothers. Women who underwent previous pregnancies often reach full dilation faster. For mothers whose pelvic openings are too narrow or display anatomical issues, cervix dilation could take some. That could lead to prolonged or arrested labor, according to Latoya Kuester, M.D., an OB-GYN with Women's Care in Yulee and Fernandina Beach, Florida.
A fetus in a breech position, or when its head is not in an orthodox position relative to the cervix, may prevent full dilation and lead to further complications during childbirth. Healthcare providers may attempt to manually reposition a breech baby or recommend a cesarean birth.
How do doctors know if you're fully dilated?
Physicians measure the extent of cervical dilation through digital cervical examination. Here, the attending obstetrician places two gloved fingers in the vagina to measure the width of the cervical opening.
The measurement helps approximately gauge the distance between cervical walls:
- 1 cm equals the width of one finger
- 3 cm equals the width of two fingers
- 4 cm equals a 1 cm space between the two fingers
Keep in mind that the typical maximum stretch between two fingers is 8 cm. When full dilation occurs at 10 cm, the cervix should not be present or blocking the front of the presenting fetal part, usually the infant's head.
Other ways to gauge cervical dilation
Some obstetricians use or recommend other methods to determine cervical dilation.
Ultrasound technology could produce more accurate results in gauging the extent of dilation, indicated a 2018 study. However, ultrasound tech in relation to cervical dilation has yet to gain widespread acceptance in modern obstetrics.
Another clinical tool used to assess cervical dilation is the Bishop score. Used in tandem with a digital cervical exam, Bishop scores can determine the probability of successful labor induction.
Factors taken into consideration to calculate the Bishop score include:
- Ripening of the cervix
- Cervical position and consistency as labor begins
- Fetal station
The highest score on the scale is 13, and the range of scores indicating the favorability of a cervix for vaginal delivery is 6 or more.
Any score less than 6 is an indication the cervical condition is unfavorable for vaginal delivery and could result in an obstetrician mandating a cesarean delivery, or when the baby is taken out through a cut, or incision, in the mother's abdomen and uterus.
Cervical effacement vs. dilation
Effacement and dilation can be confused with each other and misunderstood. Effacement measures the thinness of the cervix, while dilation measures its wideness, said Melissa May Deer Pelletier, D.O., an OB-GYN with Northwestern Medicine in Glen Ellyn, Illinois.
However, discussing dilation should go hand-in-hand with effacement.
"Both cervical effacement and dilation work in tandem during labor," Pelletier said.
Dilation occurs when the cervix opens from closed at 0 cm to full at 10 cm. During labor, the uterus must contract regularly to place pressure on the cervix, which eventually effaces or thins and opens or dilates the cervix.
Healthcare providers need the cervix to be fully effaced at 100 percent and fully dilated at 10 cm before they tell a woman to start pushing.
Conclusions on what dilation means
Each woman experiences labor differently. First-time mothers tend to have longer labors, but generally, individuals will have varying experiences. Some women will give birth in minutes, while others will experience hours-long labor.
Knowing how the cervix expands can help laboring people and their pregnancy support team better understand the delivery process.