Prostaglandins are locally acting lipid compounds derived from arachidonic acid in cell membranes. Within human reproductive tissues, particularly the myometrium and the cervix, prostaglandins E2 and F2 alpha play central physiological roles. They act as paracrine and autocrine messengers to orchestrate the complex biochemical changes required for human parturition.
Unlike systemic hormones, prostaglandins break down rapidly near their site of synthesis. They soften collagen matrices, increase local vascular permeability, and stimulate smooth muscle contraction. Understanding this local action helps midwives appreciate why specific synthetic analogs are administered directly into the vagina or cervix rather than given orally or intramuscularly for cervical preparation.
Before uterine contractions can successfully dilate the birth canal, the firm, closed cervix must undergo a structural transformation known as cervical ripening. A Bishop score below six traditionally indicates an unfavorable, unripe cervix that requires pharmacological preparation before labor induction.
During ripening, prostaglandins trigger an inflammatory-like reaction. This biochemical cascade causes several distinct changes:
Labor induction involves the artificial initiation of uterine contractions before spontaneous labor begins. When the cervix is unfavorable, prostaglandins serve as primary ripening agents. By softening the cervix and simultaneously stimulating low-frequency myometrial contractions, they often initiate true labor without needing subsequent oxytocin.
Midwives must carefully evaluate the clinical indication for induction, such as post-term pregnancy, hypertensive disorders of pregnancy, or suspected fetal growth restriction. The overall goal is achieving a vaginal delivery safely while minimizing risks to both mother and baby.
Two primary prostaglandin analogs are used in obstetric practice: dinoprostone and misoprostol.
Precise dosing prevents catastrophic uterine rupture or fetal distress. Misoprostol is typically administered vaginally or orally in low microgram doses—usually 25 micrograms every four to six hours. Vaginal administration provides a more gradual, sustained release than oral routes, though oral solutions are gaining popularity in specific protocols.
Dinoprostone gel is placed directly into the posterior fornix of the vagina, with doses repeated every six hours up to a maximum of three doses in twenty-four hours. The controlled-release pessary stays in place for up to twenty-four hours unless active labor or hyperstimulation supervenes. Midwives must always verify the exact medication strength, as misoprostol tablets intended for stomach ulcers come in much higher milligrams and must never be used whole for induction.
Continuous surveillance is mandatory during prostaglandin administration. Before inserting any ripening agent, the midwife must confirm a reactive fetal heart rate tracing and document baseline uterine activity.
Following insertion, electronic fetal monitoring (cardiotocography) is typically required for at least thirty to sixty minutes to ensure the fetus tolerates the initial drug exposure. Intermittent auscultation or continuous monitoring continues according to institutional guidelines. Midwives must also monitor maternal vital signs, charting temperature, pulse, and blood pressure regularly because prostaglandins can occasionally induce mild pyrexia or shivering.
While effective, prostaglandins carry significant clinical risks. The most dangerous complication is uterine hyperstimulation, which can lead to fetal hypoxia, meconium aspiration, and uterine rupture. Gastrointestinal side effects like nausea, vomiting, and diarrhea also occur frequently because systemic prostaglandin receptors are present in the gut.
Certain conditions make prostaglandin induction completely unsafe. Absolute contraindications include:
Uterine hyperstimulation is defined as tachysystole (more than five contractions in ten minutes averaged over thirty minutes) accompanied by non-reassuring fetal heart rate patterns. When this emergency occurs, immediate action saves lives.
Management steps include: