Cervical Length Assessment

TTTS. Step Three: Cervical Length Assessment

The third aspect of the ultrasound evaluation of patients with TTTS involves an adequate Figure 7.10 (a) Pulsatile umbilical venous flow. (b) Pulsatile umbilical venous flow in the umbilical vein and absent end-diastolic velocity in the umbilical artery in the same view. (See also color plate section, page xxv.) assessment of the cervical length. 

Because of the early gestational age at which patients would typically present, transabdominal assessment of the cervical length is usually adequate. However, we prefer to document the cervical length via transvaginal ultrasound unless there are specific contraindications for doing so. 

Assessment of the cervical length is particularly important because, in addition to fetal demise, miscarriage or premature labor is the second mechanism responsible for pregnancy loss in TTTS. A short cervical length may be secondary to uterine contractions or from ‘cervical incompetence’ as a mechanical result of the overdistention of the uterus (Figure 7.14). 

Although our data shows a statistically significant inverse correlation between cervical length and the degree of polyhydramnios as measured by the MVP, the association is not strong (R = ?0.139). Nonetheless, it does suggest that a short cervical length may indeed be partly explained by a mechanical phenomenon. Therefore, we recommend that patients with a cervical length <2.5 cm undergo a cervical cerclage prior to referral. 

If a cervical length <2.5 cm is found incidentally during the evaluation, we may choose to place a cerclage at the time of the laser surgery or the following day, to allow potential benefit of the concomitant amnioreduction. Because of this management algorithm, our data show no difference in outcome relative to a cervical length less or greater than 2.5 cm.