Uterus and Cervix
20.1 Cervical Incompetence and Shortening
Description and Clinical Features
Cervical incompetence (also termed cervical insufficiency) is defined by the American College of Obstetricians and Gynecologists as the inability of the uterine cervix to retain a pregnancy in the second trimester, in the absence of uterine contractions. Cervical incompetence has traditionally been diagnosed primarily based on a history of recurrent mid-trimester pregnancy losses.
Obstetrical ultrasound, via the finding of a shortened cervix (one measuring less than 20–25 mm in length in the second trimester), can determine that a woman is at elevated risk of preterm birth even in the absence of prior pregnancy losses. This sonographic finding can lead to pregnancy management decisions that potentially improve pregnancy outcome.
 Figure 20.1.1 Cervical shortening demonstrated by transabdominal sonography. A: Measurement (calipers) when there is no funneling. B: In another patient, the cervix is dilated along its entire length (*), with no residual closed cervical length. The partially filled bladder (BL) provides a sonographic window for visualizing the cervix. |
Sonography
The sonographic technique for measuring cervical length is described in an earlier section of this Atlas. This section focuses on the identification of a short cervix, measuring less than 20–25 mm in length. While a short cervix can be identified on transabdominal sonography (Figure 20.1.1), transvaginal sonography (Figure 20.1.2) is the preferred approach
to cervical length assessment. In particular, transvaginal sonography should be used when evaluating a woman who has risk factors for preterm birth.
to cervical length assessment. In particular, transvaginal sonography should be used when evaluating a woman who has risk factors for preterm birth.
 Figure 20.1.2 Cervical shortening demonstrated by transvaginal sonography. A: Measurement (calipers) of shortened cervix without funneling. B: In the presence of funneling (arrows), the cervical length (calipers) is measured from the end of the funnel to the external os. The amnion (arrowheads) is seen within the funneled cervix. |
The cervix is measured from the internal to the external os (Figures 20.1.1A and 20.1.2A). If the internal os is dilated and the dilatation extends partway towards the external os (a finding known as “funneling”), cervical length is measured as the length of the closed portion of the cervix. That is, it is measured from the closed end of the funnel to the external os (Figure 20.1.2B).
 Figure 20.1.3 Spontaneously changing cervix. A: Sagittal transvaginal view of the cervix demonstrates a cervix measuring 2.64 cm in length (caliper). B: Approximately 20 seconds later, the cervical canal is dilated (*), mainly at the internal os. C: Forty seconds after that, the cervix is even more dilated (*), with little or no residual closed cervix. |
The length and shape of the cervix may change during the course of the sonogram. This can occur spontaneously (Figure 20.1.3) or may be elicited by manual pressure on the
uterine fundus (Figure 20.1.4). In either case, cervical length should be taken to be the shortest length of the cervix during the sonogram.
uterine fundus (Figure 20.1.4). In either case, cervical length should be taken to be the shortest length of the cervix during the sonogram.
Care must be taken not to put too much pressure on the cervix with the transvaginal transducer. If the inner portion of the cervix is open, transducer pressure can squeeze it closed, thereby spuriously increasing the cervical length. This can result in failure to detect a short cervix (Figure 20.1.5).
 Figure 20.1.4 Cervix dilating with fundal pressure. A: Sagittal transvaginal view of the cervix demonstrates a normal appearing cervix measuring 3.00 cm in length. B: With manual pressure on the uterine fundus (W/ PRES), the cervix shortened to 2.18 cm in length. |
 Figure 20.1.5 Transvaginal transducer pressure closing an open cervix. A: Transvaginal sonogram demonstrates cervical funneling (*), with the length (calipers) of the residual closed cervix measuring 1.55 cm. B: When the cervix is compressed (COMP) by the transvaginal transducer, funneling disappears and the length (calipers) of the apparently closed cervix increases to 3.02 cm. |
20.2 Fibroids (Leiomyomas) in Pregnancy
Description and Clinical Features
Fibroids are common benign myometrial tumors. They are often asymptomatic during pregnancy. In some cases, however, they can lead to pregnancy complications, including the following:
Pregnancy loss: The risk of pregnancy failure is somewhat elevated in the presence of fibroids.
Pain: Fibroids will, at times, cause considerable pain during pregnancy. This may be due to the tendency of fibroids to grow during pregnancy, because fibroid growth is often hormonally dependent. The pain is especially severe when a growing fibroid outstrips its blood supply and necroses centrally, becoming a degenerating fibroid.
Obstruction of vaginal delivery: A large lower segment or cervical fibroid may obstruct vaginal delivery.
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