A short cervix during pregnancy is a condition where the cervix, the lower part of the uterus, measures shorter than a typical length. This condition is associated with an increased likelihood of preterm birth, which occurs before 37 weeks of pregnancy. Understanding the reasons a cervix might shorten is important for managing pregnancy.
Understanding Cervical Length
Cervical length refers to the measurement of the cervix from its internal opening (internal os) to its external opening (external os). This measurement provides insight into the cervix’s ability to remain closed and support the pregnancy until term. Healthcare providers typically measure cervical length using transvaginal ultrasound during prenatal care.
A cervical length measurement is usually taken during the second trimester of pregnancy, often between 18 and 24 weeks. While cervical length naturally changes throughout pregnancy, a measurement of less than 2.5 centimeters before 24 weeks gestation is generally considered a short cervix. This measurement is a primary way healthcare providers assess a person’s risk for preterm birth.
Structural and Congenital Factors
Some individuals may have a cervix that is inherently shorter or weaker due to structural or developmental factors present from birth. These are known as congenital conditions. For instance, certain uterine anomalies, such as a bicornuate uterus or a septate uterus, involve an unusually shaped uterus that can affect the integrity and function of the cervix.
A bicornuate uterus, characterized by a heart-shaped appearance, might lead to an altered cervical structure or a weaker lower uterine segment. Similarly, a septate uterus, which has a wall dividing the uterine cavity, can sometimes be associated with cervical changes. In some cases, the cervical tissue itself may simply be weaker than average, a condition often referred to as cervical insufficiency, which can cause the cervix to shorten and open prematurely without contractions. These inherent anatomical variations can directly contribute to a cervix being shorter during pregnancy.
Medical History and Procedural Influences
A person’s past medical history and prior medical procedures can also influence cervical length during pregnancy. Previous surgical interventions on the cervix, such as a loop electrosurgical excision procedure (LEEP) or a cone biopsy, are notable factors. These procedures remove abnormal or precancerous cells from the cervix, but they can also remove a significant amount of cervical tissue, resulting in a physically shorter cervix.
Additionally, a history of previous spontaneous preterm birth or second-trimester pregnancy loss may indicate underlying cervical insufficiency. The cervix may have demonstrated a tendency to shorten or open prematurely in past pregnancies. Furthermore, carrying multiple fetuses, such as twins or triplets, places increased pressure and strain on the cervix. This additional weight and distension can contribute to cervical shortening, as the cervix must support a greater load.
Inflammation and Infection Pathways
Inflammation and infection represent another pathway through which the cervix can shorten during pregnancy. The presence of certain infections, even those that might not cause obvious symptoms, can trigger an inflammatory response within the cervical tissue. For example, bacterial vaginosis or urinary tract infections have been linked to changes in cervical integrity.
When an infection occurs, the body’s immune system releases inflammatory mediators that can affect the collagen and other structural components of the cervix. This inflammatory process can lead to a softening and weakening of the cervical tissue, potentially causing it to efface (thin out) and dilate (open). Subclinical infections, which are present without overt symptoms, can also contribute to chronic inflammation and gradual cervical remodeling, ultimately leading to a shortened cervix. The ongoing biological changes initiated by these pathways can compromise the cervix’s ability to maintain its length and strength throughout pregnancy.