Common abnormalities of fetal kidney development include renal pelvis dilatation, hydronephrosis, renal agenesis, ectopic kidney, congenital pelvic ureteral junction obstruction, vesicoureteral junction obstruction, etc. Most scholars believe that renal pelvis dilatation with an anterior and posterior diameter of >15mm is highly suggestive of obstructive lesions. Most scholars believe that the anterior and posterior diameters of renal pelvic dilatation >15mm are highly suggestive of obstructive lesions, which are mostly seen in renal pelvic ureteral junction obstruction, vesicoureteral junction obstruction, vesicoureteral reflux, and so on, and the rate of postpartum surgery is high. Anterior and posterior renal pelvic dilatation of 10 to 14 mm is also suggestive of renal disease, and postnatal neonatal follow-up is recommended. If the anterior and posterior diameters of renal pelvic dilatation are 4~10mm, it may be normal or physiologic, but it does not exclude the possibility of severe urinary tract obstruction. It is best to follow up 5~7 days after delivery. Renal agenesis Bilateral renal agenesis fetuses do not survive after birth and mainly die of severe pulmonary dysplasia. If unilateral renal agenesis is not combined with other malformations, the prognosis is good and the fetus can survive normally without affecting the life expectancy. Ectopic kidney refers to the change of the location of the kidney, which can be ectopic to the pelvic cavity or thoracic cavity. The prognosis is better and usually asymptomatic, but the incidence of urinary tract infection increases significantly after the birth of ectopic kidney. 4, congenital renal pelvic ureteral junction obstruction Whether unilateral or bilateral obstruction, the prognosis is better. The degree of fetal renal pelvic dilatation does not always correlate with postnatal infant renal function, but in general the more severe the intrauterine dilatation, the worse the neonatal renal function. Changes in the degree of dilatation should be closely monitored in late pregnancy, and the prognosis is poor if bilateral obstruction is combined with low amniotic fluid. Ultrasound and renal function should be routinely checked after delivery. 5, vesicoureteral junction obstruction, the prognosis is good, more than 40% of cases can be relieved or disappear without treatment. If the internal diameter of ureter is <6mm in prenatal examination, most of the cases do not need surgical treatment after delivery; if it is more than 10mm, the prognosis is relatively poor, and most of the cases need surgical treatment.