it is extremely important to assess the cervical length as a shortened cervix puts the mother at a high risk for for preterm delivery.
as the pregnancy progresses the length changes.
saloman et.al (2009) developed a model for singleton pregnancies after assessing 6614 cervical length measurements across multiple gestational ages. these results are shown in the graph and table below.
reference: salomon, l.j., diaz-garcia, c., bernard, j.p. and ville, y. (2009), reference range for cervical length throughout pregnancy: non-parametric lms-based model applied to a large sample. ultrasound obstet gynecol, 33: 459-464. https://doi.org/10.1002/uog.6332