Outcome of antenatally diagnosed fetal renal pelvic dilatation at a tertiary fetal medicine unit

The authors retrospectively analysed the outcome of antenatally diagnosed renal pelvic dilatation (RPD) defined as ≥5 mm at routine anomaly scan from July 2007 to December 2008. There were 43 cases divided into three groups. Resolved RPD antenatally and/or normal postnatal scans not requiring referral to paediatric urology per our protocol. Persistent postnatal dilatation on conservative management. Persistent postnatal pathology requiring surgery. Group 1 (N=22) was the largest group. Out of 22 cases, 20 had mild dilatation (less than 10 mm) and 2 had moderate dilatation (11 and 12 mm) at 20-week gestation. Of those with mild dilatation, majority (N=19) had dilatation less than 7 mm. The dilatation was bilateral in seven cases. Amniocentesis was accepted by one third of patients and was normal. Four cases of mild dilatation had resolved by 30 weeks. Postnatally, majority of these babies had normal scan findings by week 4–10 of age (N=21). In one baby, RPD resolved by 4 months of age. Groups 2 (N=15) and 3 (N=6) had RPD greater than 7 mm at 20 weeks and was associated with worsening antenatal dilatation and/or other features as dilated ureter/calyces, echogenic cortex, tense bladder and progressive decrease in liquor volume. These babies continue to be under follow-up. The authors therefore believe the FASP proposed cut off from our current threshold of antenatally diagnosed RPD from 5 to 7 mm is appropriate. By changing this cut off the authors would not have missed any cases of postnatal pathology and avoided unnecessary postnatal scans and parental anxiety.