From the Guidelines
Vaginal progesterone, regardless of whether administered as a capsule or tablet, is effective in preventing preterm labor, with the choice between formulations being a matter of patient and provider preference. The key to effectiveness lies in consistent administration and proper placement high in the vagina, rather than the specific formulation used 1. Vaginal progesterone works locally to reduce uterine irritability, decrease inflammation, and inhibit cervical ripening that can lead to preterm birth.
When considering the use of progesterone for preventing preterm labor, it's crucial to understand that both capsules and tablets can be used vaginally, with dosages typically ranging from 100-200 mg for capsules and 100-400 mg for tablets or suppositories, administered once daily. The medication's local action allows for targeted delivery to the uterus with fewer systemic side effects compared to oral administration. Some patients may prefer one formulation over the other due to comfort or convenience, but clinically, the outcomes are similar.
It's also important to note that the use of progesterone in certain high-risk cases, such as those with a history of preterm birth or a short cervical length, has been studied, and guidelines recommend its use in specific scenarios 1. However, the most recent and highest quality evidence supports the use of vaginal progesterone based on patient and provider preference, without a strong distinction between capsule and tablet formulations in terms of efficacy for preventing preterm labor 1.
The critical factor in the effectiveness of vaginal progesterone, whether in capsule or tablet form, is adherence to the prescribed regimen. Patients should be advised on the proper use and potential effects, such as discharge from oil-based capsules, to ensure compliance and maximize the benefits of the treatment. Ultimately, the decision between a progesterone capsule and tablet for vaginal use should be made based on individual patient needs and preferences, with the understanding that both can be effective in preventing preterm labor.
From the Research
Comparison of Progesterone Capsule and Tablet for Preterm Labor
- The provided studies do not directly compare the effectiveness of progesterone capsules and tablets administered vaginally for preventing preterm labor.
- However, the studies discuss the use of vaginal progesterone in various forms, including capsules and gels, for preventing preterm birth in high-risk women 2, 3, 4, 5.
- One study from 1985 compared the use of 17 alpha-hydroxyprogesterone caproate (a form of progesterone) administered via intramuscular injection to a placebo, and found that it significantly reduced the rate of premature deliveries 6.
- Another study published in 2023 found that vaginal progesterone, in the form of a gel or soft capsules, may be beneficial in reducing the risk of preterm birth in women with a short cervix, but not in unselected twin gestations or singleton gestations with a history of spontaneous preterm birth and a cervical length >25 mm 2.
- A 2023 systematic review and meta-analysis found that vaginal progesterone does not prevent preterm birth or improve perinatal outcomes in unselected twin gestations, but may reduce the risk of preterm birth and adverse perinatal outcomes in twin gestations with a short cervix 4.
- A 2025 argument for the use of vaginal progesterone for prevention of preterm birth in women with a history of preterm birth, regardless of cervical length, suggests that prophylactic vaginal progesterone may be beneficial in these cases, but notes that current recommendations are conflicting 5.
- A 2020 review of progestogens for preventing preterm birth notes that while some randomized trials support the use of vaginal progesterone, the largest trials have not demonstrated efficacy, and there is limited data on long-term effects 3.