Thursday, January 10, 2013
Posted by: Jaime Kean, MD
One of our Facebook fans asked us to address the topic of labor induction and how it is related to the risk of having a cesarean delivery. The short answer: it depends.
Normally it is best to wait for labor to naturally occur. There are many situations, however, when waiting for labor to occur on its own has risk either for the mother or the baby. In these situations, obstetricians and midwives will use medications to induce a woman’s labor. Our goal is for the woman to have a vaginal birth. The likelihood of this occurring is a function of many variables, including whether a woman’s water has broken spontaneously or if it is still intact and whether this is her first vaginal delivery or she has had a successful vaginal delivery in the past.
The best predictor of successful induction (one that leads to a vaginal delivery), however, is the status of the cervix prior to induction. Obstetricians and midwives evaluate the cervix according to four factors that are determined during a physical exam: dilation, effacement, consistency and position of the cervix in the birth canal. Each factor is rated on a scale and assigned a point value. When combined, the point values are known as the Bishop score. The Bishop score is the best available tool to assess the cervix and predict the likelihood that an induction will lead to a vaginal delivery.
Here are the characteristics of the cervix that your provider is evaluating to determine the Bishop score:
- Dilation: This is the measurement of how much the cervix has opened in preparation for birth. In late pregnancy, the cervix may dilate up to three centimeters. During labor, uterine contractions and pressure from the baby cause further dilation. Ten centimeters is considered completely dilated. In the Bishop model, the highest point value is assigned to dilation of five centimeters or more, while the lowest values are assigned to a completely closed cervix or one that is dilated to one or two centimeters.
- Effacement: This refers to thinning or shortening of the cervix. Normally, the cervix is about four centimeters long. As effacement occurs, the cervix shortens. Effacement is measured as a percentage; 0% means the cervix hasn’t shortened at all, while 100% means it has become very thin. The highest point value is assigned to 80% or greater effacement.
- Consistency: Here’s where prior vaginal delivery plays a role. Consistency of the cervix is measured as “firm,” “medium” or “soft.” For young women and those who have never had a vaginal delivery, the cervix is typically more firm and resistant to stretching. For older women or those who have had a prior vaginal birth, the cervix is typically softer and dilates easier during labor.
- Position: This is determined as “anterior” (easy to reach during an internal exam), “midposition,” or “posterior” (way in the back – hard to reach during a physical exam).
The final component of the Bishop score isn’t related to the status of the cervix but the position of the baby in the birth canal, referred to as “fetal station.” Higher point values are assigned to women whose babies have dropped lower.
The four characteristics of the cervix described above plus fetal station are assessed and combined to create the Bishop score. If the Bishop score is high (five or greater), then the likelihood of vaginal delivery is the same whether the labor is spontaneous or induced (meaning there is no increase in the risk of cesarean section). If the Bishop score is less than five, there is an increased risk of cesarean section; however, studies of women who have already had one vaginal delivery have a low risk of cesarean section with induction, regardless of their initial cervix exam.
There are things your provider can do to increase the likelihood of a successful induction when your cervical condition is not favorable (low Bishop score). These techniques are designed to promote cervical “ripening” (dilation and effacement). They include hormonal agents known as prostaglandins, or mechanically dilating the cervix using a Foley catheter balloon. These techniques may be used together with intravenous oxytocin (“Pitocin”) to induce labor.
For women who have never had a vaginal delivery and who have a low Bishop score, there is an increased risk of c-section associated with labor induction. When it comes to the health or you or your baby, the benefits of labor induction may outweight these risks. In the end, our goal is the same as yours – healthy mom, healthy baby.
Dr. Jaime Kean is a board certified OB/GYN physician and surgeon who sees patients at the Tabor office of Women’s Healthcare Associates. She went to medical school and completed her OB/GYN specialty training at Case Western Reserve University. When she's not helping families have healthy babies, she enjoys spending time with her children, volunteering in their school and helping with Girl Scouts.
Sources: Image - She Knows