Assessment of a cervicometer compared to transvaginal ultrasound in identifying women with a short cervical length: a multicenter study

BACKGROUND: Preterm birth remains a major cause of neonatal morbidity and mortality worldwide. Short cervical length (CL) as measured by transvaginal ultrasound (TVU) in the second trimester represents the single most predictive risk factor for spontaneous preterm birth. Previous studies have addressed, in part, the limitations of TVU availability by utilizing a cervicometer to screen patients for short cervix, identifying those patients who may not benefit from TVU CL screening. In view of the prior studies indicating that a cervicometer measurement may have a high negative predictive value (NPV) for a sonographically short cervix, we sought to identify the ideal cervicometer threshold value in a prospective, multicenter study. OBJECTIVE: The primary objective was to determine the cervicometer CL measurement threshold that provides a high NPV for the identification of patients who are highly unlikely to have a TVU CL measurement <= 20 and <= 25 mm and, therefore, may forego TVU. STUDY DESIGN: This prospective study, executed in 5 US centers, included 401 women >= 18 years of age who provided written informed consent to undergo CL measurement in the mid trimester. All women underwent both cervicometer- and TVU-measured CLs by individuals blinded to results of the other measurement. Both measurements were performed at 17-23 weeks' gestation (visit 1) and repeated at 24-29 weeks' gestation (visit 2). All TVU measurement images were reviewed by a central reader. Test characteristics and receiver operating characteristic curves were created to determine and confirm the optimal cervicometer CL threshold, maximizing the NPV. RESULTS: In all, 358 subjects were evaluable at visit 1 and 267 at visit 2. At visit 1, the average TVU CL was 38.7 +/- 7.6 mm and the average cervicometer CL was 30.3 +/- 8.8 mm. Similar measurements were seen at visit 2. Receiver operating characteristic curves were utilized to graphically identify a cervicometer CL threshold of 30 mm that maximized sensitivity while minimizing the false-positive rate. The 30-mm cervicometer CL threshold provided a 98-100% NPV and 0.0 negative likelihood ratio for identification of women who have a low likelihood to have a sonographic short cervix (ie, transvaginal CL <= 20 mm or <= 25 mm). The 17-23 weeks' gestation 30-mm cervicometer CL threshold has 100% sensitivity, 4546% specificity, and 1.8 and 0.0 positive and negative likelihood ratios to predict sonographic CL <= 20 and <= 25 mm. CONCLUSION: Cervicometer CL screening successfully identifies women at low risk for short transvaginal CL. Use of a 30-mm threshold by cervicometer CL measurement confers a 98-100% NPV, with high sensitivity and moderate specificity to predict a TVU short CL. Cervicometer measurement of CL may permit almost 50% of women to avoid TVU

A New Series of Uranium Isotope Reference Materials for Investigating the Linearity of Secondary Electron Multipliers in Isotope Mass Spectrometry

A new series of gravimetrically prepared uranium isotope reference materials, the so-called IRMM-074 series, with the n(235U)/n(238U) isotope ratio held constant at unity and the n(233U)/n(238U) isotope ratios varying from 1.0 to 10-6 has been prepared and certified. The methods for the preparation, the mixing and the certification are described. Additionally, recent observations regarding the linearity response of secondary electron multipliers (SEM) and suitable reference materials for investigating detector linearity are reviewed. Two measurement procedures for applying the IRMM-072 and IRMM-073 (diluted from the remaining fraction of IRMM-072) series as well as the new IRMM-074 series for assessing SEM linearity are described. The procedures are tailor-made for the specific instrumental characteristics of Thermal Ionization Mass Spectrometers (TIMS) and Multiple-Collector Inductively Coupled Plasma Mass Spectrometers (MC-ICPMS) but can be adapted also for further types of isotope ratio mass spectrometers.JRC.D.4-Isotope measurement