Which of the following is a risk factor for preterm birth?

Short cervical length less than 25 mm is a well-established risk factor for preterm birth. The length of the cervix can indicate the likelihood of early labor, as a shorter cervix is associated with a higher chance of cervical incompetence and the potential for premature delivery. When the cervix cannot maintain its length and firmness, it may begin to efface and dilate earlier than expected, leading to preterm labor and delivery.

In this context, identifying short cervical length through ultrasound can serve as a critical component of risk assessment and management in pregnant individuals who are at higher risk for preterm birth. Interventions can be initiated, such as progesterone supplementation or cervical cerclage, to help prolong the pregnancy if a short cervix is identified.

In contrast, while factors like increased maternal age, high body mass index, and a history of cesarean delivery may have implications for maternal and fetal health, they are not as directly correlated with the mechanism leading to preterm birth as cervical length measurements are.