I can’t remember how many times I’ve talked to these anxious parents, since the baby was still in the mother’s womb, I think. I vaguely remember the first time they came to my clinic, mom was full of anxiety, dad was helpless, and grandparents and grandparents, everyone’s face was clouded with gloom. It turns out that the mother was found to have fetal hydronephrosis at 30 weeks of pregnancy. In the era of advanced network, a lot of information can be easily obtained, but less than alleviate the anxiety of the parents of the baby, but make them more confused. I understand this feeling, after all, I am also a parent, but as a doctor, I do not feel that this disease has too much risk. At first, I didn’t pay much attention to it, but just tried to explain it to them as clearly as possible, drawing sketches and looking for pictures of typical cases in my phone, and talking for almost half an hour with a dry mouth. In fact, in clinical work, this is just a very common situation, but the busy schedule always makes you overlook many details. Fetal hydronephrosis is a relatively common malformation of unknown origin, most of them are found around 25-30 weeks of pregnancy. Generally, a separation of the renal pelvic collecting system of more than 15mm after 27 weeks is considered severe hydronephrosis, and the chances of surgery increase after birth. But this does not mean that as long as the child has hydronephrosis over 15mm, he or she will definitely be operated on! According to the follow-up data, less than 1/5 of the total number of births with hydronephrosis found during prenatal checkups require surgery, and this percentage will continue to decrease as the follow-up data is improved! So, don’t worry, don’t worry, don’t worry, don’t worry, don’t worry! In the past, the awareness of hydrocele was passive, but now, with the perfection of perinatal examination and the improvement of ultrasound technology, more and more hydrocele is detected early and followed up, which is a good thing, so that hydrocele, a congenital malformation, can be actively treated under the follow-up surveillance of doctors. In fact, there is still controversy about the treatment of hydrocele in the fetal period after birth, and this controversy is growing, with the focus on the choice of the timing of surgical intervention, which centers on the preservation of renal function! In the past, it was often believed that the dilated renal pelvis compressed the renal parenchyma and made it thinner, and if the thickness of the renal parenchyma was less than 4 mm, damage to the renal units might occur, which in turn caused renal function damage. However, this view is now increasingly questioned. A recent review of the literature suggests that renal failure due to hydronephrosis alone is almost non-existent. Instead, it is believed that hydronephrosis actually cushions and protects renal function. So now the indications for surgery have become more and more stringent, not only by the size of the dilated renal pelvis and the amount of thickness of the renal parenchyma as indicators, but more by the trend of hydronephrosis! Trend! After so many cases of patient follow-up and summary, my current treatment generally suggests that the post-birth follow-up of fetal hydronephrosis should at least follow the following principles: no matter what the degree of hydronephrosis is 3-5 days after birth, the ultrasound must be reviewed 42 days after birth and analyzed according to the results of two ultrasound examinations, combined with the results of prenatal ultrasound. If the hydrocele becomes stable or shrinking trend, it is recommended to extend the follow-up time and review the ultrasound after 3-6 months; if the hydrocele becomes growing trend, review it after one month and follow the general follow-up in the above way when it is stable; if it still continues to grow, review it again at one month interval and enter the surgery preparation mode. It is generally recommended to operate after the child’s third month of age if possible, regardless of the hydrocele condition. Surgery in infants and children is very damaging, with more complications, and surgery also requires a good physical condition. Combining surgery and the child’s physical condition, surgery in March is not recommended unless it is a last resort. The kidneys are hardly involved in the excretion of metabolic waste in the body during fetal life because there is a placenta that helps the fetus to excrete metabolic waste despite the mother’s body. The kidneys start working only after birth, and the kidney excretory capacity usually peaks at 8 months of age after the child’s first birth. Therefore, it is likely that fetal hydronephrosis will increase after birth as the child’s renal excretion increases, and this may be one of the reasons for the worsening of hydronephrosis. Therefore, more and more pediatric urologists recognize that it is possible that an increase in hydronephrosis after birth does not necessarily mean that immediate surgery is needed, but instead, follow-up observations can be made until after 8 months of age to remove the factors that increase renal excretion before the hydronephrosis becomes truly pathologic. This is one of the arguments for not recommending premature aggressive surgery. There is also a question about urinary tract infections due to hydronephrosis. Many reports have mentioned that repeated urinary tract infections may develop pelvic scarring and cause renal failure. Summarizing the current literature, the following points are summarized: 1. the cases of urinary tract infections caused by hydronephrosis are extremely rare, a small probability event and negligible; 2. urinary tract infections are indeed associated with secondary renal scar formation, but they do not increase the incidence of renal failure; 3. urinary tract infections in infants and children are not a serious condition and do not need to be trivialized.