Induction of labor: Clinical sciences

Induction of labor is the initiation of parturition through the use of medications and other processes that mimic normal labor. This procedure can be done when the benefits of delivery outweigh the risks of continuing a pregnancy. Depending on the patient’s initial cervical exam, you may need to ripen the cervix or stimulate contractions with a variety of methods. Ultimately the goal of labor induction is to have a spontaneous vaginal delivery.

Okay, when a pregnant patient presents for induction of labor, you should assess if there are any contraindications present before doing anything.

Contraindications are conditions that prevent a safe vaginal delivery, such as transverse fetal lie, non-reassuring fetal status, or umbilical cord prolapse.

Here’s a clinical pearl! An umbilical cord prolapse occurs when the umbilical cord falls below the presenting part of the fetus, usually through a dilated cervix into the vagina. This is an obstetric emergency that needs immediate C-section delivery!

Additional contraindications include patients with previous disruption of the myometrium, including a prior classical c-section with a uterine incision, a prior myomectomy entering the uterine cavity, or a prior uterine rupture. These patients are at a high risk of uterine rupture during labor, which makes induction inadvisable.

Additionally, some patients may have abnormal placentation, such as a placenta previa, where the placenta covers the cervical os and bleeds profusely if cervical dilation occurs; as well as abnormal vascular presentation like vasa previa, where the umbilical vessels are unprotected and found in the membranes that cover the cervical os. Others may have conditions such as invasive cervical cancer, which can block the cervical os and obstruct the ability of a fetus to pass through the birth canal, while also increasing the risk of severe maternal hemorrhage.

Another contraindication is an active viral disease that can be passed to the fetus during delivery. This includes an HIV viral load of more than 1000 in the third trimester; or an active herpes simplex virus infection, specifically, if HSV lesions are present in the genitourinary tract or if a patient experiences prodromal symptoms like genital burning or pain.

Finally, do not induce patients with a gestational age less than 39 weeks, unless they have a medical indication for delivery, like preeclampsia. Elective induction can be performed at 39 weeks if gestational age has been confirmed.

Here’s a clinical pearl to keep in mind! Fetal morbidity increases starting at 41 weeks, so induction of labor should be revisited with patients who haven’t yet delivered by that time, and induction of labor is definitely recommended if spontaneous labor has not begun by 42 weeks due to the increased risk of stillbirth.

Okay, if a contraindication is present, do not proceed with induction of labor. Instead, consider c-section delivery or in cases of fetal malpresentation, an external cephalic version may be attempted. On the other hand, if contraindications are absent you can proceed with an induction of labor. Your first step is to perform a cervical exam and calculate the Bishop score.

Let’s look at how to proceed once we calculate the Bishop score.

This is a scoring system based on a set of criteria noted on the vaginal exam that predicts the likelihood of successful induction of labor. The Bishop score is helpful in deciding how to start an induction. There are five criteria to consider: cervical dilation, which describes how many centimeters open the cervix is; the position of the cervix within the vaginal canal; the effacement of the cervix indicating how thin the cervix is; the station of the fetal head within the pelvis; and the consistency of the cervix, which softens as labor begins. Each one is given from 0 to 3 points, and the total value is known as the Bishop score. Of note, cervical dilation is considered the most important of the five scoring elements.

Let’s first look at an unfavorable Bishop score. If the Bishop score is 6 or less, the cervix is considered unfavorable. This means you will need to perform cervical ripening before the induction process. In normal parturition, the cervix will soften, thin, dilate, and move anteriorly. Cervical ripening facilitates that process, which increases the likelihood of a successful induction of labor. This can be done with pharmacological agents or mechanical methods of cervical ripening.

The most commonly used ripening agent is a synthetic prostaglandin E1 analogue called misoprostol. It can be administered either by mouth, buccally, or inserted into the vagina. In addition to ripening the cervix, misoprostol will stimulate uterine contractions. There is also a prostaglandin E2 analogue available called dinoprostone, which works similarly. Dinoprostone is available in a vaginal form only.

Here’s a clinical pearl! Even though prostaglandins increase the likelihood of vaginal delivery within 24 hours, they actually don’t reduce the rate of C-section delivery, and there’s an increased risk of uterine tachysystole. This is defined as more than five contractions in 10 minutes. If sustained, this can cause fetal distress and you may need to administer a tocolytic, like terbutaline, to relax the uterine muscle. Also, keep in mind that all prostaglandins are contraindicated in patients who had a prior c-section but who otherwise qualify for a trial of labor after C-section, as prostaglandin use raises the risk of rupture.