Vaginal and cesarean delivery are the two ways that a baby can be born. With vaginal delivery, the baby comes into the world through the mother’s vagina, or birth canal, and the process is called labor, whereas with cesarean delivery, also called a c-section, surgery is done to get the baby out.
Now, generally speaking, vaginal delivery is the preferred option.
But in some cases, complications may arise during labor, or a vaginal delivery may be contraindicated in the first place, and a c-section may be done.
And finally, a c-section may be performed on maternal request.
Ok, now, vaginal delivery, or labor, has three stages.
Stage I is when the cervix dilates to 10 centimeters, and it’s divided into a latent phase, covering dilation from 0 to 6 centimeters, and an active phase, when the cervix dilates completely.
Stage II is when the fetus passes through the birthing canal.
If everything goes well, the baby is delivered and labor progresses to stage III, which is the delivery of the placenta.
Complications that may arise during labor come in two flavors.
First, labor may fail to progress as expected, and second, there may be non-reassuring fetal status, sometimes called fetal distress, during delivery; and both are indications for a C-section.
So, in the first category, the indications are active phase arrest and prolonged second stage.
Active phase arrest means there’s there’s no cervical change during the active phase after 4 hours of adequate uterine contractions, or 6 hours without adequate uterine contractions.
Remember that adequate uterine contractions are higher than 200 Montevideo units, or MVU.
A prolonged second stage, on the other hand, is when it takes longer than 3 hours in primiparas and 2 hours in multiparas for the baby to descend through the birth canal.
In this case, an emergency C-section is indicated if the fetal head is not engaged, meaning it hasn’t reached the inlet of the pelvic brim during that time.
Now, the second category refers to non-reassuring fetal status during labor.
Fetal status can be indirectly assessed through the fetal heart rate. This can be done through auscultation or electronic fetal monitoring.
With auscultation, an obstetric stethoscope is used to assess the fetal heart rate intermittently throughout labor, like every 30 minutes.
Alternatively, an electronic fetal monitor is used to monitor the fetal heart rate continuously throughout labor.
This is preferable for high risk pregnancies, when there is pregnancy associated pathology, or when labor fails to progress as expected.
Now, normally, fetal heart rate is between 110 and 160 beats per minute, it increases during contractions, and it returns to normal after a contraction.
If the heart rate is too slow, too fast, fails to increase during contractions, or fails to return to normal after a contraction, that may signify a non-reassuring fetal status, and a c-section may be needed.
Ok, now let’s see when vaginal delivery may be contraindicated in the first place.
First, there’s maternal indications, like a previous c-section, obstructive lesions of the lower genital tract, transmissible maternal infections, or preexisting cardiac disease.
With a previous c-section, the uterine muscle has been incised before, so there’s an increased risk of uterine rupture and hemorrhage during labor, or after delivery.
However, recent studies have shown that in individuals with a single previous c-section, who have a current singleton pregnancy in a cephalic presentation, and who haven’t had uterine rupture after previous deliveries, vaginal delivery is a safe option.
Obstructive lesions of the lower genital tract may refer to cervical or vaginal cancer, vulvovaginal condylomas, obstructive vaginal septa or large uterine fibromas that distort the lower uterine segment and perturb fetal head engagement during delivery.
Fetal indications for a c-section include abnormal fetal presentation, congenital malformations or skeletal disorders and signs of infection.
Abnormal fetal presentations include breech presentation, which is when the baby’s buttocks are the presenting part right above the cervix, rather than their head.
Of note, if breech presentation is detected during a routine ultrasound performed between 28 and 36 weeks gestation, external cephalic version should be tried first, before indicating a cesarean delivery.