Prevalence:

• Unilateral: 1 in 2,000 births.
• Bilateral: 1 in 5,000 births.

Ultrasound diagnosis:

• Unilateral: nonvisualisation of one kidney with normal bladder and amniotic fluid. Color Doppler demonstrates single renal artery. There may be compensatory hypertrophy of the contralateral kidney.
• Bilateral: nonvisualisation of the kidneys and bladder in combination with anhydramnios >17 weeks’ gestation. Failure to visualise renal arteries with colour Doppler. Adrenal glands assume discoid shape and move laterally and inferiorly. Small fetal chest, cardiac hypertrophy and talipes are seen.

Associated abnormalities:

• In the majority of cases, renal agenesis is a sporadic and isolated abnormality.
• Chromosomal defects, mainly trisomy 18, are found in 1-2% of cases.
• Associated syndromes are found in 10% of cases. The most common are: Fraser syndrome (autosomal recessive condition characterized by renal agenesis, laryngeal atresia, cryptophthalmos, syndactyly) and VACTREL association (vertebral and ventricular septal defects, anal atresia, tracheoesophageal fistula, renal anomalies, radial dysplasia and single umbilical artery), MURCS association (sporadic; hypoplastic or bicornuate uterus,  renal agenesis or dysplasia, vertebral and rib abnormalities).

Investigations:

• Detailed ultrasound examination.
• Karyotyping in cases with additional abnormalities.

Follow up:

• In isolated cases follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Bilateral is lethal, usually in the neonatal period due to pulmonary hypoplasia.
• Unilateral has normal prognosis. In some patients there may be vesicoureteric reflux. Girls should have a pelvic ultrasound to look for abnormalities in the Müllerian structures postnatally.

Recurrence:

• Non-syndromic: 3%.
• In 15% of cases, one of the parents has unilateral renal agenesis and in these families the risk of recurrence is increased.