Introduction Existing tests for the prediction of preterm birth (PTB) are suboptimal – many exhibit poor predictive values. Electrical impedance spectroscopy (EIS) objectively quantifies the composition of the cervix. A prospective cohort study, funded by the MRC (DPFS scheme) has commenced in Sheffield to assess its potential predictive utility for preterm birth.

Methods Employing an optimised prototype, 250 women at high risk of PTB will undergo spectroscopy readings at 20–22 and 26–28 weeks; 250 low risk women once at 20–22 weeks; and 100 symptomatic women following admission to hospital. To determine whether cervical impedance (CI) could prove a platform technique, we will also assess fetal fibronectin and ultrasound cervical length (CL). Concurrent qualitative and health economic studies will establish the acceptability of CI measurement.

Results For asymptomatic women we will determine: the gestation at which CI measurement is most predictive of PTB; the optimum predictive electrical frequencies for CI assessment; the most predictive CI cut-off values; the predictive capacity of CI vs. ultrasound CL for PTB and whether a combination of both tests offers better predictive performance. The primary outcome is prediction of birth <37 weeks. Secondary outcomes include prediction of birth <32 weeks, birthweight <2500 g, premature rupture of membranes, NICU admission, composite perinatal morbidity/mortality, maternal hospitalisation, cost effectiveness/utility, tocolysis and cervical cerclage. For symptomatic women we will assess prediction of delivery within 1 and 2 weeks of assessment and delivery <37 weeks.

Conclusions EIS is a promising clinical tool – our study will rigorously assess its role in the antenatal care of pregnant women.