Table of Contents
Page created on January 5, 2022. Last updated on December 18, 2024 at 16:57
Definition and epidemiology
Labour can be induced, i.e. forced to start earlier than it would physiologically, with the help of certain medications and procedures. This is done if there is a medical indication for why pregnancy should not progress further, because the risk to the mother or foetus would be higher than the risk of induction if pregnancy would be allowed to continue.
Planned/scheduled/elective/daytime delivery refers to when the delivery of a term (> 39 week) foetus is induced in the absence of a medical indication, usually performed on the mother’s wish. It’s only an option in low-risk, term pregnancies. A common indication for this is that the mother lives far away from the hospital, or if her previous births have been very rapid (to prevent labour from occuring out of the hospital).
Before labour is induced, it’s important to evaluate whether vaginal birth is contraindicated or not, as there’s no point inducing vaginal labour if a C-section is necessary anyway.
In Norway, approximately 1 in every 4th birth is induced.
Possible indications for labour induction
- Prelabour rupture of membranes (PROM)
- Post-term pregnancy
- Hypertensive disorder of pregnancy (preeclampsia)
- Oligohydramnios
- Intrauterine growth restriction
- Diabetes in pregnancy
- Twin gestation
Cervical ripening
Before inducing labour, it’s important to estimate how ripe the cervix is already. If the cervix is ripe, we can proceed to induction. If the cervix is not ripe enough, we must use techniques to stimulate cervical ripening. A ripe cervix is soft, dilated, and short. How “ready” the cervix is for induction is scored with the Bishop score.
Ripening of the cervix results from a cascade of physiological changes. The mechanism is not well known, but prostaglandins are involved. Prostaglandins also stimulate myometrial contractility, which is important in the next stage of labour.
One of the methods of induction of cervical ripening is application of a balloon catheter. The balloon tip of a regular urinary (Foley) catheter is placed within the internal cervical os, between the foetal membrane and uterine wall, and is inflated with water. This is left in place for 24 – 36 hours. The balloon and the pressure it exerts irritate the cervix, stimulating release of prostaglandins.
Another method is the use of prostaglandins (misoprostol). These may be administered vaginally or per os and stimulate both cervical ripening and myometrial contractility. The dose of prostaglandin may be repeated.
The ripeness of the cervix is regularly monitored while these techniques are being used. When the cervix has been sufficiently ripened, labour can be induced.
Methods of induction
In some cases, labour begins without intervention after the cervix has ripened.
The two options for induction of labour are continuous IV oxytocin infusion and amniotomy (intentionally rupturing the membrane). Both or either of these are sufficient to induce labour.
Stripping of the membranes refers to using a finger to stretch the cervix and loosen the foetal membranes from the uterine wall. This may be used for induction only if the cervix is already dilated, and as such is usually only an option for inducing post-term pregnancies.
Contraindications
If vaginal birth is contraindicated, labour induction is contraindicated.
- Malpresentation
- Severe disorder of the mother
- Foetal distress on CTG
- Cephalopelvic disproportion
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