A physiological link between uterine perfusion and endocervical length reveals a novel interaction during early...

Endocervical length is a strong predictor of spontaneous preterm birth, yet the physiological processes shaping its baseline architecture during early placentation remain unclear. We explored whether endocervical length relates to uterine perfusion in first-trimester pregnancies, assessed by vascular resistance-based measurements and quantitative uterine artery (UtA) blood flow volume.

In a prospective cohort of 446 consecutive pregnancies undergoing ultrasound examination between 6 and 13 weeks' gestation, UtA impedance indices and blood flow volume were measured using pulsed-wave color Doppler and volumetric color power angio M-mode ultrasound techniques, respectively. Standardized transvaginal endocervical length was measured at the same visit.

Endocervical length remained stable between 5 and 10 weeks (median 24 mm, 95% confidence interval (CI) = 22-27) and increased by 11 and 13 weeks (median 27 mm, 95% CI = 26-27; p = 3.19 × 10^-8), in keeping with physiological transition from hypoxic to perfused intervillous environment. Total UtA blood flow volume showed a strong positive linear correlation with endocervical length (p = 3.12 × 10^-8), with differences detectable from 6 weeks onwards and confirmed after z-score standardization and multivariable adjustment. Marked perfusion differences were observed at extreme endocervical length values, with lower total UtA flow z-scores ≤25th percentile (-0.5) and higher values > 75th percentile (0.1; both p < 0.001). In contrast, UtA pulsatility index showed no association with endocervical length.

First-trimester endocervical length is independently associated to UtA blood flow volume but not to resistance-based Doppler impedance indices. This divergence underscores the physiological distinction between perfusion and impedance-derived measurements in early pregnancy and suggests coordinated regional adaptations during early uteroplacental remodeling.