Isolated mild fetal pyelectasis detected by transvaginal sonography in advanced maternal age

Diagnostic accuracy of fetal renal pelvis anteroposterior diameter as a predictor of significant postnatal nephrouropathy: second versus third trimester of pregnancy

OBJECTIVE

The objective of the study was to determine the most effective fetal renal pelvis anteroposterior diameter thresholds and the best gestational age in predicting significant neonatal nephrouropathy and neonatal nephrouropathy requiring surgery.

STUDY DESIGN

Eighty-three newborns with prenatal ultrasound evidence of unilateral or bilateral fetal renal pelvis dilatation (anteroposterior diameter 4 mm or more) before the 26th week of gestation were systematically and prospectively investigated prenatally and postnatally.

RESULTS

Receiver operating characteristic curve analysis showed that third-trimester anteroposterior diameter cut-offs were more reliable than second-trimester cut-offs in predicting significant neonatal nephrouropathy, the best threshold being 8 mm. No significant differences were found between the 2 trimesters in the screening of fetuses at risk of neonatal nephrouropathy requiring surgery.

CONCLUSION

Significant neonatal nephrouropathy is better predicted at the third trimester, the best threshold being 8 mm, but the screening of patients at greater risk of surgery is also possible during the second trimester. An anteroposterior diameter of 11 mm or more, with an odds ratio of 128.33 (95% confidence interval 11.68 to 1408.98), is a very effective cut-off and a reliable prognostic indicator of neonatal nephrouropathy requiring surgery, even before the 26th week.

The role of the second trimester genetic sonogram in screening for fetal Down syndrome

The Genetic Sonogram is an ultrasound examination done on second trimester fetuses that not only evaluates the fetus for structural malformations, but also searches for the sonographic markers of fetal Down syndrome. The main markers that comprise the genetic sonogram include the nuchal fold, short femur and humerus, pyelectasis, hyperechoic bowel, echogenic intracardiac focus, and any major abnormality. The absence of any marker on a second trimester scan conveys a 60-80% reduction in prior risk of Down syndrome based on advanced maternal age or serum screen risk. The presence of sonographic markers, either singly or in combination, will raise the baseline risk of Down syndrome using likelihood ratios calculated for each individual marker. Using this approach, approximately 75% of fetuses with Down syndrome can be identified by modifying the patient's baseline risk according to the results of the ultrasound. The second trimester scan will likely continue to play an important role in the future in the detection of aneuploidy.

Controversial ultrasound findings

This article has reviewed a few of the more controversial findings in the field of obstetric ultrasound. For each one evidence-based strategies for the management of affected pregnancies have been suggested, derived from what the authors believe is the best information available. In some cases, this information is very limited, which can make counseling these patients extremely difficult. Some physicians find using specific likelihood ratios helpful in these complex discussions. An example of the relative likelihood ratios for several markers of trisomy 21 is illustrated in Table 10. Although the management of each of the findings discussed in this article is different, a few generalizations can be made. To begin with, the detection of any abnormal finding on ultrasound should prompt an immediate detailed ultrasound evaluation of the fetus by someone experienced in the diagnosis of fetal anomalies. If there is more than one abnormal finding on ultrasound, if the patient is over the age of 35, or if the multiple marker screen is abnormal, an amniocentesis to rule out aneuploidy should be recommended. Of the six ultrasound findings reviewed here, the authors believe that only echogenic bowel as an isolated finding confers a high enough risk of aneuploidy to recommend an amniocentesis in a low-risk patient. The other findings in isolation in a low-risk patient seem to confer only a modest increased risk of aneuploidy, if any, and this risk is certainly less than the risk of unintended loss from amniocentesis. Wherever possible, modifiers of this risk, such as maternal age, history, and first and second multiple marker screening, should be used to define more clearly the true risk of aneuploidy. As obstetric ultrasound moves forward, particularly into the uncharted waters of clinical use of three- and four-dimensional ultrasound, one can expect a whole new crop of ultrasound findings with uncertain clinical significance. Clinicians are well advised to await well-designed studies to determine the clinical significance of these findings before altering clinical care.