Fetal Kidneys Ultrasound Appearance in the First Trimester - Clinical Significance and Limits of Counseling

Abstract

Objective: The objective of this study was to determine the visualizing rate of fetal kidneys at various gestational ages in late first trimester (FT) and to establish the clinical significance of their two-dimensional ultrasound (2DUS) appearance in the FT.

Methods: In a prospective cross-sectional study, 1456 women from an unselected population underwent a detailed assessment of fetal anatomy at 11+0 -13+4 weeks of gestation with the use of transabdominal sonography. Information on the ultrasound findings, antenatal course and perinatal outcome was obtained in 1331 cases.

Results: 44 cases in which a congenital kidney disease was detected by ultrasound in the prenatal period were identified. The renal pathology was suspected in the FT in 8 cases, and confirmed by a standard test (postmortem autopsy or second-trimester scan) in 4 cases. The standard detailed second-trimester scan at 18-22 weeks diagnosed another 23 cases but refuted suspicion in 4 FT positive cases. The third trimester added another 17, all confirmed by the postpartum scan. For FT presence or absence of congenital renal anomalies, sensitivity, specificity, +LRs and -LRs of 2DUS were 9.09%, 99.69%, 29.25, and 0.91.

Conclusion: FT prenatal kidneys' visualization is critically dependent on the gestational age. FT diagnosis holds uncertainty. An early diagnosis carries a risk of providing a false-positive or a false-negative result, because the differentiation of the renal system is delayed or the diagnosis is not amenable yet to prenatal ultrasound. No FT findings can exclude the mid-trimester follow-up ultrasound scan. Second and third trimester scan are relevant for congenital kidney diseases.

Keywords: fetal kidneys; first trimester anomaly scan; first trimester ultrasound; multicystic dysplastic kidney; polycystic kidney disease; prenatal counseling.

Figure 1

Flow diagram (recommended for accuracy studies)

Figure 2

Visualization rates at different gestational age, in the late first trimester.

Figure 3

Cases screened positive at first trimester detailed anomaly scan. Aspects in the follow-up program and outcome.

Figure 4

Sensitivity, specificity, positive and negative likelihood ratio values and diagnostic odds ratio with 95% CI for 2DUS method in detecting congenital renal anomalies.

Figure 5A

Case 1, ultrasound features at 11+3 gestational weeks (first row) and at 16+2 gestational weeks (second row) -11+3 weeks of amenorrhea scan: gray-scale 2D examination showed unilateral increased echogenicity of the renal cortex, with pyelectasis appearance, antero-posterior diameter of the right renal pelvis 1.7 mm, normal bilateral renal length. No other associated structural abnormalities were noted in terms of genetic markers and structural features. CRL (crown-rump length) was consistent with menstrual dates (59.4 mm). The mother’s kidneys appeared normal. -16+2 weeks of amenorrhea scan: unilateral multicystic dysplastic kidney (MCDK) (right kidney), contralateral borderline pyelectasis (left kidney).

Figure 5B

Case 1, intact specimen obtained after medical termination of pregnancy, pathological examination. Macroscopic (first row) and microscopic (second row) aspects at autopsy. The diagnosis was confirmed.

Figure 6A

Case 3, ultrasound features at 12+4 gestational weeks (first row) and at 16+5 gestational weeks (second row) - 12+4 weeks of amenorrhea. Gray-scale 2D examination showed unilateral pyelectasis appearance, antero-posterior diameter of the right renal pelvis 4.4 mm, normal bilateral renal length and echogenicity of the renal cortex. No other associated structural abnormalities were observed at the detailed anomaly FT scan. The mother’s kidneys appeared normal. -early second trimester scan: the diagnostic was suspicion of unilateral pyeloureteral duplicity and renal cyst (right kidney), normal left kidney.

Figure 6B

Case 3, postpartum findings showed right unilateral pyelectasis and cortical cyst and normal left kidney.

Figure 7A

Case of unilateral MCDK, ultrasound examination negative in the FT. - 12+0 WA: normal kidneys (first row) - 18+3 WA: bilateral hydronephrosis, mild on the left kidney. The right kidney moderate hydronephrosis and dilation of the right ureter.

Figure 7B

Same case, unilateral MCDK, postpartum aspects, after unilateral nephrectomy; microscopic confirmation.

Figure 8

Case of Potter syndrome. FT detailed anomaly scan showed a single umbilical artery, normal kidney images, no structural anomaly.

Figure 9

Case 2. Ultrasound kidneys’ features at 12+3 WA: mild bilateral pyelectasis. Multiple associated additional markers for chromosome anomaly (cardiac anomaly, clenched hands, hypoplastic nasal bone) were found. Karyotype (from chorionic villus sampling) at 12+4 WA confirmed trisomy 18. Postmortem autopsy revealed horseshoe kidneys.