Endocrinology and Endocrine System
Optimizing Obstetric Care: A Narrative Review of Immediate and Sustained Release Oral Micronized Progesterone
Abstract
Girija Wagh, Ratnabali Chakravorty, Kavitha Lakshmi Easwaran and Jasleen Kaur Malhotra
Oral natural micronized progesterone (NMP), commonly administered as immediate-release (IR) soft gelatin capsules, is widely used across reproductive and obstetric indications, offering a patient-friendly alternative to vaginal and parenteral routes. However, conventional IR formulations are limited by variable bioavailability and central nervous system (CNS)- related adverse effects due to first-pass hepatic metabolism. Sustained-release (SR) oral NMP formulations are developed to overcome these limitations. These formulations utilize polymer-based matrices to provide gradual progesterone release over 16-24 hours, resulting in stable serum concentrations, reduced peak-trough fluctuations, once-daily dosing, and improved tolerability. These pharmacokinetic advantages may enhance treatment convenience and adherence, particularly in settings requiring prolonged hormonal support. Clinically, oral NMP-SR plays an important role in luteal phase support (LPS), threatened abortion, recurrent pregnancy loss, and prevention of preterm birth. Evidence from randomized and observational studies indicates that oral NMP SR provides pregnancy outcomes comparable to vaginal progesterone in selected settings, particularly in LPS. In other indications, findings are more heterogeneous; however, available data and real-world experience suggest favourable clinical utility. Across indications, oral NMP-SR formulations appear to offer improved tolerability and dosing convenience. Overall, oral NMP-SR represents a practical and patient- friendly option, offering consistent systemic exposure and improved tolerability across key obstetric indications.