Why are many pediatric hydronephrosis detected during ultrasound in pregnancy? There are several physiological factors that contribute to fetal hydronephrosis being seen on ultrasound during fetal life: the fetus produces excessive urine due to low glomerular reabsorption rate, which increases 10-12 times from 20-40 weeks of gestation, 3 times from 20-25 weeks, and 2-3 times from 30-40 weeks; the hydrated state of the mother and the degree of filling of the fetal bladder also play a role in the expansion of the fetal pelvis, resulting in a dilated fetal pelvis seen on ultrasound Progesterone has a relaxing effect on the smooth muscle of the urethra, which is one of the causes of hydronephrosis in pregnant women, and progesterone also affects the fetal urinary tract, leading to smooth muscle relaxation and pelvic dilatation; the ratio of male to female fetal pelvic dilatation is 2:1, because the increased pressure of the male fetal bladder can lead to distortion of the vesicoureteral junction. This is because the increased pressure of the male fetal bladder can cause distortion of the vesicoureteral junction, resulting in a higher incidence of fetal vesicoureteral reflux (VUR), which is manifested by ultrasound as a dilated renal pelvis. More than 80% of fetal VURs diagnosed during fetal life are male. Most fetal hydronephrosis due to these factors resolves spontaneously after birth. The etiology of hydronephrosis found in the fetus is complex: it includes physiological transient hydronephrosis (which may gradually resolve and subside, accounting for 50-70% of cases), ureteropelvic junction obstruction (10-30% of cases), vesicoureteral reflux (10-40% of cases), ureterobladder junction obstruction (5-15% of cases), polycystic dysplastic kidney (2-5% of cases), posterior urethral valve (1-5% of cases), duplication kidneys with or without ureteral cysts (1-3%), and rare causes include: ectopic ureter, urethral atresia, Megan’s belly syndrome, polycystic kidneys, and renal cysts. Should I terminate my pregnancy if hydronephrosis is found in the fetus? Fetal hydronephrosis found in the fetus usually does not require termination of pregnancy. The main disease requiring intervention in the fetus is posterior ureteral valve, if there is amniotic fluid reduction and normal karyotype, singleton, and salvageable renal function by ultrasound and urine examination, intervention is possible; if it is infantile polycystic kidney or bilateral dysplastic kidney, termination of pregnancy is usually required. Does fetal hydronephrosis need to be reviewed during pregnancy and after birth, and how often? What are the main investigations? Overall, if hydronephrosis is detected in mid-pregnancy (anterior-posterior pelvic diameter > 4 mm), it is necessary to review ultrasound in late pregnancy to evaluate whether the hydronephrosis is progressing. Moderate to severe hydronephrosis (anterior-posterior pelvic diameter > 1 cm) detected in early pregnancy requires repeat ultrasound; anterior-posterior pelvic diameter > 7 mm detected in late pregnancy suggests further investigation after birth; any anterior-posterior pelvic diameter of 10 mm or dilated calyces during pregnancy should be treated with caution and further investigation should be performed after birth. Most hydrocele found during pregnancy is born without clinical symptoms; therefore, children with normal urinary feeding should not be discontinued because they are observed to be voiding and feeding! All fetuses with hydrocele at birth require a first choice of urologic ultrasound to assess the extent of hydrocele and decide on the next step of follow-up plan according to the extent of hydrocele. For male infants with bilateral severe hydronephrosis, dilated bladder, suspected posterior urethral valves, and those with postnatal clinical symptoms such as febrile infection, elevated creatinine, weakness in urination, and difficulty in urination, ultrasound should be performed immediately after birth. If there is an increase in hydrocele, to what extent does it increase and require medical intervention? If the hydronephrosis increases gradually during follow-up; if the pelvis and calyces are dilated and the renal parenchyma is thin, no improvement is observed during follow-up; if clinical symptoms (e.g. urinary tract infection, lumbar and abdominal pain) appear; if the fractional renal function is < 40% or decreases by more than 5%; if bilateral severe hydronephrosis or severe hydronephrosis in isolated kidneys, surgical intervention is considered What symptoms are present as a basis for consultation? The fetal hydronephrosis found before birth needs further examination after birth, no hydronephrosis found before birth, but after birth, symptoms such as urinary tract infection, lumbar and abdominal pain, hematuria, and difficulty in urination need to be seen. Mostly physiological hydronephrosis or vesicoureteral reflux Hydronephrosis surgical treatment modalities Pyeloureteral junction obstruction leading to hydronephrosis Current surgical treatment is usually pyeloureteroplasty, i.e. removal of the narrowed pyeloureteral junction and performing pyeloureteral anastomosis. Both open surgery and laparoscopic-assisted surgery can be used. We currently use minimally invasive surgery for the treatment of hydrocele in children older than 3 months of age, and the success rate of surgery is over 98%.