A short cervix during pregnancy increases the risk of premature birth. Progesterone, a naturally occurring hormone, is increasingly recognized for its role in mitigating this risk. This article explores its function and effectiveness in supporting pregnancies with a shortened cervix.
Understanding a Short Cervix and Preterm Birth Risk
A short cervix measures less than 2.5 centimeters, typically before 24 weeks of pregnancy. The cervix, a cylindrical tissue connecting the uterus to the vagina, normally remains long and firm, acting as a protective barrier for the developing fetus. Its premature shortening can indicate cervical insufficiency.
Early cervical shortening significantly increases the likelihood of preterm birth, defined as delivery before 37 weeks of gestation. Preterm birth carries health implications for infants, as their organs may not be fully developed. These babies face higher risks of complications including breathing problems, neurological disorders like cerebral palsy, developmental delays, and increased susceptibility to infections.
Progesterone’s Action in Preventing Preterm Birth
Progesterone is a hormone that plays a central role in maintaining a healthy pregnancy. Initially, the corpus luteum produces it, and later the placenta takes over. This hormone is crucial for preparing the uterine lining for implantation and supporting early fetal development.
Progesterone prevents preterm birth in women with a short cervix through several mechanisms. It helps maintain uterine quiescence, keeping the uterus relaxed and preventing premature contractions. This is achieved by dampening the electrical activity of myometrial cells and downregulating agents involved in uterine contraction.
The hormone also exerts anti-inflammatory effects within the cervix, as inflammation can contribute to cervical ripening and premature changes. Progesterone can reduce inflammatory cell infiltration and suppress the production of certain inflammatory chemicals. It influences cervical integrity by affecting collagen, the primary structural component of the cervix, contributing to cervical softening and elasticity.
Clinical Outcomes of Progesterone Therapy
Clinical trials and meta-analyses consistently show progesterone therapy effectively reduces preterm birth risk in women with a short cervix, especially in singleton pregnancies. Vaginal progesterone significantly lowers the rate of preterm birth at various gestational ages. Some studies indicate a reduction in the risk of preterm birth before 33 weeks by as much as 42%. This treatment also improves neonatal outcomes, leading to reduced rates of respiratory distress syndrome, lower birth weight, and fewer admissions to the neonatal intensive care unit.
For twin pregnancies, vaginal progesterone can also be beneficial for those with a short cervix. Meta-analyses indicate it reduces the risk of preterm birth, neonatal complications such as respiratory distress syndrome, and even neonatal death in this specific subgroup. For example, a 31% reduction in deliveries before 33 weeks and a 47% reduction in neonatal death have been observed. Routine progesterone use is not generally recommended for all twin pregnancies, only for those with a short cervix.
Administering Progesterone and Important Considerations
Progesterone for a short cervix is most commonly administered vaginally, available as suppositories or gels. Intramuscular injections of a synthetic progestin, 17-alpha-hydroxyprogesterone caproate (17-OHPC), are used for other indications but are not effective for a short cervix.
Treatment typically involves a daily dose of vaginal progesterone, from 90 to 200 milligrams. Therapy usually begins once a short cervix is identified (between 16 and 24 weeks) and continues until approximately 34 to 36 weeks. Candidates are generally women with a singleton pregnancy and a cervical length of 25 millimeters or less during a mid-trimester ultrasound. Women experiencing symptomatic uterine contractions are not candidates for this preventative therapy.
Progesterone therapy for a short cervix is generally well-tolerated and safe. While side effects are usually mild, they can include stomach upset, changes in appetite, weight gain, fluid retention, or fatigue. Serious adverse effects are rare. Vaginal progesterone is considered safe during pregnancy.