As for the problem of hydronephrosis that you care about, at the end of the third month, the occurrence and evolution of organs such as kidney and ureter have been completed, and then the embryo enters the mature stage. At gestational age 18 weeks, the kidney begins to urinate, and the urine enters the renal pelvis and flows to the bladder through the ureter. When the bladder is full of urine, it will be discharged through the urethra. Under the B-ultrasound image, the fetus can sometimes see the process of urination.
Under normal circumstances, when the fetus is urinating, B-ultrasound can also see the separation of renal pelvis; When the fetus excretes urine, the separation of renal pelvis may disappear. Generally speaking, if the separation of renal pelvis is within 10 mm, it is physiological. Don't worry about this situation, just check the B-ultrasound regularly. If the separation of renal pelvis exceeds 65438±0.6mm, further examination is needed to determine whether the fetus has abnormal development of kidney, ureter and other organs.
Congenital hydronephrosis refers to incomplete obstruction at the junction of renal pelvis and ureter. Urine in the renal pelvis cannot be discharged smoothly, which leads to the increase of renal pelvis pressure. Over time, the renal pelvis slowly expands, forming hydronephrosis. When the obstruction is serious, hydronephrosis is often large. There are many reasons for obstruction, most of which are congenital defects in the upper ureter, such as the contraction of mucosa in the ureter to form a valve; The muscular layer of the tube wall is abnormal in structure and development, too thick or scarred, or the peristalsis function is defective. A few are external pressures, such as vascular ectopic, congenital umbilical cord scar compression, and finally cause obstructive hydronephrosis. Fetal hydronephrosis can be mild, only 1 ~ 2 cm, or as large as 7 ~ 8 cm. A few fetuses with bilateral severe hydronephrosis, due to fetal urinary retention, can reduce urine volume, so amniotic fluid volume can also be reduced. Oligohydramnios can also cause fetal lung, chest and other dysplasia, leading to multiple fetal malformations in a malignant environment.
With the development of modern science and technology, the diagnosis of hydronephrosis can be carried out early and accurately. Prenatal ultrasound is almost non-invasive and the most convenient and economical examination. In our country, this examination has been popularized to the primary maternal and child health care centers and has been listed as a routine prenatal examination. After about 6 months of pregnancy, the fetal kidney will secrete urine. If hydronephrosis occurs because of hydronephrosis, it is very easy to find it under B-ultrasound, and its size and location can be accurately known, so it can be rechecked many times in a short time. Fetuses suspected of hydronephrosis can be tracked in time after birth. Other imaging examinations, such as CT and MRI, are rarely needed before delivery, but intravenous pyelography or CT and MRI should be done after birth, especially before perioperative operation, to make a clear diagnosis.