Induction of labor (IOL) is a critical obstetric technique utilized to trigger uterine contractions artificially after fetal viability but prior to the spontaneous onset of labor. It is primarily aimed at achieving cervical effacement and dilatation to facilitate vaginal delivery. This intervention is often necessary in various clinical scenarios, like post-term pregnancies, preeclampsia, gestational diabetes, intrauterine growth restriction, or maternal medical conditions that pose risks to the mother or fetus. Globally, IOL is performed in up to 25% of pregnancies, highlighting its importance in modern obstetrics . In Europe, the rates of IOL vary significantly, ranging from 7% to 33%, reflecting differences in healthcare systems, clinical guidelines, and patient demographics .
The success of IOL is heavily influenced by the condition of cervix at the time of induction. Cervical status is assessed using the Bishop's scoring system, which evaluates factors like cervical dilatation, effacement, consistency, position, and fetal station. A favorable cervix, characterized by a Bishop's score of 6 or higher, is related to an elevated probability of successful vaginal delivery. In contrast, an unfavorable cervix (posterior, firm, and long) presents significant challenges, decreasing the chances of vaginal birth and increasing the risk of cesarean delivery.
Cervical ripening is a fundamental process that prepares the cervix for labor by increasing its softness and distensibility. This process is controlled by a complex interplay of hormonal, biochemical, vasodilatory and inflammatory alterations. Endogenous prostaglandins (PGs), produced by uterus, cervix, fetal membranes and placenta, have a pivotal role in these changes. PGs stimulate the breakdown of collagen fibers, increase water content, and promote the release of cytokines and other inflammatory mediators that facilitate cervical remodeling. When natural ripening is insufficient, iatrogenic methods are employed to induce cervical ripening and labor. These methods include mechanical agents, such as Foley catheters, cervical dilators, or amniotomy, and pharmacological agents, such as prostaglandins, oxytocin, and smooth muscle stimulants like herbs or castor oil.
Despite its widespread use, IOL is not without risks. Common challenges include ineffective labor induction, prolonged labor, and excessive uterine activity, which may result in complications like fetal distress, uterine rupture, and an elevated probability of cesarean delivery. Prostaglandins, which mediate their effects through specific G protein-coupled receptors (GPCRs), are integral to the inflammatory and immune responses that drive cervical ripening .
However, the therapeutic utilization of natural PGs is restricted by their quick metabolism, chemical instability, and short half-life, as well as their propensity to cause side effects like vomiting, diarrhea, nausea, and uterine hyperstimulation .
To overcome these limitations, synthetic prostaglandins have been developed and are widely used in clinical practice. Misoprostol, a synthetic analog of prostaglandin E1 (PGE1), is the most frequently utilized agent due to its stability, cost-effectiveness, and ease of administration. It is available in oral, sublingual, and vaginal forms, making it a versatile option for labor induction. Misoprostol is particularly effective in low-resource settings because of its affordability and stability at room temperature. However, its use requires careful dosing to avoid complications such as uterine hyperstimulation and fetal distress .
Dinoprostone, a synthetic analog of prostaglandin E2 (PGE2), is another widely used agent, particularly in settings where controlled release and fewer side effects are desired. Dinoprostone is available in gel, insert, and suppository forms, allowing for tailored dosing based on individual patient needs. It is often preferred in cases where a slower, more controlled induction process is warranted. However, dinoprostone is more expensive than misoprostol and requires refrigeration, which can limit its use in resource-constrained settings.
