2 Indications and current treatments
2.1 Induction of labour is the most commonly performed obstetric intervention. It is done in up to 20% of pregnancies in the UK and is generally carried out when the risks of continuing pregnancy outweigh the benefits. It is usually more painful than spontaneous labour, and epidural analgesia and assisted delivery are more likely to be needed. Maternal and fetal indications for induction of labour include pregnancy‑induced hypertensive disorders, diabetes, post‑term pregnancy, thrombophilia, intrauterine fetal growth restriction, oligohydramnios, non‑reassuring fetal status and fetal death.
2.2 Various methods are used to ripen and dilate the cervix and successfully induce labour in women when the cervix is unfavourable for induction. These include pharmacological methods (prostaglandins in the form of vaginal gels or tablets, or pessaries, and oxytocin as a slow intravenous infusion), surgical methods (amniotomy, alone or with oxytocin) and mechanical methods (laminaria tents and balloon catheters introduced through the cervix into the cervical canal and the extra‑amniotic space). The aim of mechanical interventions is to ripen and dilate the cervix and promote onset of labour by applying pressure on the internal cervical os, by indirectly increasing local secretion of prostaglandin and oxytocin, or both. Also, mechanisms that involve neuroendocrine reflexes may promote the onset of uterine contractions. A standard Foley urinary catheter is commonly used, with the balloon inflated in the extra‑amniotic space. The catheter is then put under tension to pull back against the cervical os. Sometimes saline solution is infused into the extra‑amniotic space as an adjunct.