In high-risk singleton gestations a cervical length of < or = 2.5 cm was equal to other sonographic cervical parameters in its ability to predict spontaneous preterm birth and was better for the prediction of earlier forms of prematurity (at < 28 and < 30 weeks) than later forms (at < 32 and < 34 weeks). The optimal cervical lengths and their performance for predicting prematurity may be influenced by obstetric risk factors.

In twin gestations a cervical length of < or =2.0 cm measured between 15 and 28 weeks' gestation was at least as good as other ultrasonographic cervical parameters at predicting spontaneous preterm birth. The high specificities indicate that cervical length was better at predicting the absence than the presence of various degrees of spontaneous prematurity.

Receiver operator characteristic curves for both clinical and sonographic predictions of macrosomia subsume areas between 0.81 and 0.95, significantly larger than the area of 0.5 that indicates a useless test. Thus, these tests are defined as useful from a statistical point of view. Prediction of macrosomia by clinical or imaging techniques, however, is limited by the substantial false-positive and false-negative rates inherent in these tests. We recommend that physicians continue to use clinical methods to estimate fetal weight, including asking women with parity to provide their own estimates. We recognize that the relative error associated with clinical or sonographic estimates of fetal weight limits their use in clinical practice. Sonographic laboratories may improve their results by performing ROC curve analysis on their own data and by selecting cutoff values that best predict macrosomia in their setting. Serial sonographic measurements that are above the limits chosen to define macrosomia increase the likelihood that a birth weight will be macrosomic. Separate ROC curves must be generated for twins and breech presentations and for patients with diabetes to answer weight-related clinical questions such as mode and timing of delivery. Three-dimensional ultrasound and magnetic resonance imaging are expected to generate ROC curves for estimates of fetal weight that are better than those for two-dimensional ultrasound or clinical estimates. Such analyses have yet to be published.

Preamniocentesis counseling should emphasize the fact that, for most women, the actual pain and anxiety experienced during the procedure are significantly lower than expected. In fact, on a scale of 0-10, the mean level of pain was only 2.1, with a slightly higher mean level of anxiety.