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This study was undertaken to determine the accuracy of our previously published and prospectively validated institution-specific singleton transcerebellar diameter (TCD) nomogram in the prediction of gestational age (GA) in twin pregnancies. We further evaluated whether the prediction of GA in twin gestations using the singleton TCD nomogram differs between monochorionic and dichorionic twins.In our previously published studies, we retrospectively constructed a cross-sectional nomogram using TCD measurements in 24,026 well-dated, singleton fetuses, and prospectively validated the nomogram using 2,597 singleton fetuses. The current study comprised of 1,278 well-dated twins (19.6% monochorionic) seen in our ultrasound unit between August 1994 and May 2003, and the singleton TCD nomogram was validated in these twin gestations. The actual GA was subtracted from the GA predicted by the TCD nomogram and the concordance between actual and predicted GAs was assessed on the basis of the Pearson's correlation coefficient (r). This was performed separately for monochorionic and dichorionic twins.Concordance between the actual and predicted twin TCD measurements based on our previously published singleton TCD nomogram was high (Pearson's correlation, r = 0.95, P.0001). Between 16 and 23 weeks' gestation, the predicted mean GA was within 6 days of actual GA. Between 24 and 30 weeks, the predicted mean GA was within 3 days, and at 32 weeks or more, the predicted mean GA was within 5 days of the actual GA. Prediction of GA based on the singleton TCD nomogram was equally accurate in both monochorionic and dichorionic twin gestations (P = .686).This study demonstrates that our previously validated singleton TCD nomogram is reliable and accurate in twins irrespective of placental chorionicity.

The purpose of this study was to validate prospectively a previous retrospectively established nomogram for the prediction of gestational age using transcerebellar diameter, especially in the third trimester.In a previous study, we retrospectively constructed a cross-sectional nomogram using transcerebellar diameter measurements in 24,026 well-dated singleton fetuses. In the present study, this nomogram was validated prospectively on the basis of patients who were seen between August 2002 and May 2003 and who were carrying non-anomalous and non-malformed singleton gestations between 14 and 42 weeks (n = 2597 gestations). The actual gestational age was then subtracted from the predicted gestational age, and the concordance between actual and predicted gestational ages was assessed based on the Pearson correlation (r).Concordance between the actual and predicted gestational age was high (r = 0.92; P.0001). This agreement was superior in the second trimester (r = 0.93; P.0001) than in the third trimester (r = 0.81; P.001). Between 17 and 21 weeks, and between 22 and 28 weeks of gestation, the predicted gestational age ranged between 0 and 4 days, and between 0 and 2 days, respectively, of actual gestational age. Between 29 and 36 weeks of gestation, predicted gestational age was within 5 days of actual gestational age; at 37 weeks of gestation, the predicted gestational age was discrepant by 9 days.This prospective study demonstrates that transcerebellar diameter measurement is an accurate predictor of gestational age, even in the third trimester of pregnancy.

OBJECTIVE: Our purpose was to assess the accuracy and intraobserver variability of clinical cervical diameter measurements among obstetric health care providers. STUDY DESIGN: Polyvinyl chloride pipes 1 to 10 cm in diameter were mounted in cardboard boxes and used to simulate cervical examinations. The boxes were designed so that the examiner had to rely solely on proprioception to determine the inner diameter. RESULTS: A total of 1574 simulated cervical diameter measurements were obtained from 102 different examiners in a two-part study. The overall accuracy for determining the exact diameter was 56.3%, which improved to 89.5% when an error of ±1 cm was allowed. Intraobserver variability for a given diameter measurement was 52.1%, which decreased to 10.5% when an error of ±1 cm was allowed. CONCLUSIONS: Cervical diameter measurements obtained by digital examination are precise when an error of ±1 cm is allowed for. Intraobserver variability is >50% and is an important consideration when evaluating dysfunctional labor.

We analyzed the accuracy of four previously reported ultrasound formulas by means of abdominal circumference and/or biparietal diameter measurement for the prediction of fetal weight in the preterm infant (less than 2,000 gm). The birth weights of 25 preterm infants delivered within 72 hours of ultrasound measurement were compared to the weights calculated by formulas derived from the ultrasound measurements, and the accuracy of each formula was determined. A high degree of correlation was found or the logarithmic formulas with the use of both biparietal diameter and abdominal circumference measurement. Our data suggest that the present ultrasound methodology is of sufficient accuracy to warrant the use of ultrasonic measurement to predict fetal weight prospectively before delivery of the very low-birth weight infant. We also retrospectively reviewed the previous 4-year neonatal mortality rate for infant weighing between 500 and 2,000 gm at birth at Duke University.

Sonographic estimation of amniotic fluid volume is commonly used as a diagnostic test for oligohydramnios associated with fetal malnutrition. However, methods of measurement and diagnostic criteria are controversial. We prospectively evaluated the reproducibility of amniotic fluid diameter measurement and studied various threshold definitions of oligohydramnios as predictors of small for gestational age fetuses or fetuses with low ponderal index values. An average of the vertical and two perpendicular horizontal diameters of the largest pocket of amniotic fluid was more reproducible than the maximum vertical pocket and better enabled a single observer to differentiate between patients. An average diameter of 10 mm was highly diagnostic of small for gestational age fetuses but was insufficiently sensitive (27%) to serve as a screening test. Although also of limited sensitivity (40%), an average diameter of approximately 30 mm was probably the best screening threshold. Reduced average diameter was significantly related to the occurrence of a ponderal index less than or equal to the tenth percentile for dates. Three of seven (43%) neonates with a ponderal index less than or equal to the tenth percentile and a birth weight greater than the tenth percentile for dates had a low average diameter, suggesting that reduced average amniotic fluid diameter may help to identify the malnourished fetus with birth weight greater than the tenth percentile for dates.