Objective Antenatal ultrasound diagnosed anomalies of the kidney and urinary tract (AUDAKUT) are reported in 0.3%–5% on prenatal ultrasound (US) and 0.3%–4.5% on postnatal US. The anterior-posterior diameter of the renal pelvis (APD) is an essential measurement. Series with low threshold values of APD prenatally and postnatally will include healthy infants. It is important to avoid follow-up of such infants.

Interventions In 2006, new Danish guidelines for AUDAKUT were introduced.

Aim of study Investigations of incidences and type of AUDAKUT based on Danish guidelines, including long-term follow-up.

Design Cohort study.

Setting Copenhagen University Hospital Hvidovre and Copenhagen University Hospital Rigshospitalet, Denmark.

Patients Consecutive cases with AUDAKUT in the second and third trimesters, which were either terminated before 22 completed weeks of gestation or born in the 8-year period January 2006–December 2013. Patients were followed until June 2014.

Results 50 193 live born children and 24 terminated fetuses (0.05%) were included. The prevalence of AUDAKUT was only 0.39% prenatally, 0.29% at first postnatal US and 0.22% at the end of follow-up, including terminated cases. The greater the prenatal and postnatal APD, the higher risk of febrile urinary tract infection (fUTI) and surgical intervention, and lower probability of resolution. 25% of the identified patients had fUTI and/or surgery.

Conclusions We recommend threshold values of APD at least 10 mm in the third trimester and in general at least 12 mm at first postnatal US for intensive follow-up. In this largest to date unselected birth cohort of AUDAKUT, the incidences of clinically significant AUDAKUT were in the lowest range of those previously published.