Indeed, our mean +/− SD cervical length measurement in Group B was almost identical to that reported in the study of TTTS patients prior to treatment in which cervical length was shown to be the main predictor of very preterm delivery [13].
Study Design: A retrospective cohort study examined cervical length by means of a two-stage procedure, transabdominal ultrasonography followed by transvaginal ultrasonography if cervical length was <30 mm.
However, this reduction in uterine volume did not increase the pre-procedural cervical length at 1 hour (mean Δ: −0.1cm, 95% CI, −0.4 to 0.2) or 24 hours (0.2cm, −0.1 to 0.6) (Table 2).
Their pre-procedural cervical length did not change at one (mean Δ:−0.1cm, 95%CI, −0.4 to 0.2) or 24 hours (0.2cm, −0.1 to 0.6) after amnioreduction.
Pre-procedural cervical length did not change either at one hour (mean Δ: −0.3cm, 95% CI, −0.5 to 0.1) or 24 hours (0.2cm,−0.2 to 0.5) (Table 2).
It is known that amniotic pressure rises when the amniotic fluid index (AFI) exceeds 40 [7], but the only study of singletons with polyhydramnios (albeit largely mild as the mean AFI was only 28cm) failed to find any inverse correlation between cervical length and AFI [8].
The lack of association between the cervical length and AFI in our control group was expected, as the mean AFI was only 23cm.
Since there was a significant association between pre-procedure cervical length and AFI, and since AFI fell markedly with amnioreduction as anticipated (mean Δ = 20cm), we expected the cervix to lengthen post-procedure.
A cervical length <25 mm was found in 18 patients (41%) in the observational group at a mean gestational age of 19.1 ± 2.9 weeks' gestation.
