All or some of the urinary system is dilated. If the obstruction is complete and in early fetal period, hypoplasia and dysplasia may occur (Potter type II ).
If it occurs in the 2nd half of pregnancy hydronephrosis may develop.
Fetal urology society
Grade O: No dilatation, Grade I: Renal pelvic dilatation, Grade II: Pelvic dilatation and calyx are visible, Grade III: Renal pelvis and calyx are dilated, Grade IV: Grade III and parancime becomes thinner.
• <19 weeks: ≥5 mm.
• 20-29 weeks: ≥8 mm.
• >30 weeks: ≥10 mm(Mandell et al., 1991).
The risk of renal and urinary tract abnormality increases with:
• The severity of hydronephrosis,
• Persistence of hydronephrosis into the third trimester,
• Bilateral involvement, and
• The presence of oligohydramnios.
There may be pelvicaliciel dilatation in 1% of all fetuses.
There may be transient hydronephrosis as a result of high maternal hormone levels or excessive maternal-fetal hydration.
In hydronephrosis cases there may be ureteropelvic obstruction or vesicoureteric reflux.
If the anterio-posterior pelvis renalis diameter is >10 mm and there is pelvicaliciel dilatation, there is moderate hydronephrosis.
If hydronephrosis is diagnosed, dilatation in ureters and uretra must be detected. The size of bladder must be evaluated.
Urinary system abnormalities are generally bilateral, other kidney and amniotic fluid must be evaluated.
If it is diagnosed in 2nd trimester chromosomal abnormalities must be searched.
Vesico amniotic Shunt
Lower urinary tract outflow obstruction may develop in a fetus from pathologies such as urethral atresia and posterior urethral valves, and can be partial or complete.
Severe obstruction may lead to oligohydramnios and pulmonary and renal dysplasia.
There is uncertainty about the criteria for appropriate selection of fetuses for treatment with vesico–amniotic shunting.
Fetal lower urinary tract outflow obstruction is usually managed expectantly or by repeat vesicocentesis.
Some cases are managed by termination of the pregnancy.
The aim of a fetal vesico–amniotic shunt for lower urinary tract outflow obstruction is to decompress the obstructed bladder and restore amniotic fluid dynamics and volume, thereby preventing oligohydramnios and consequent pulmonary and renal dysplasia.
Fetal blood is also sampled for chromosomal analysis to help diagnose or exclude concomitant chromosomal abnormalities that may influence management decisions or treatment choices.