Hello Thanks for writing to us with your health concern. Fetal hydronephrosis, defined as dilatation of the renal pelvis of ≥4 mm before the 27th week of pregnancy and ≥7 mm after the 28th week of pregnancy, is the most common fetal abnormality detected on prenatal ultrasound examination, occurring with a frequency of 0.17–2.3%. Most of the time it will resolve before the baby is born. When it doesn t, most cases will resolve the first year of life. In very rare circumstances, surgery is warranted, usually to correct a problem in the ureter (which causes reflux of fluid in the kidneys, hence, the dilatation). It isn t even a major surgery. Thus, if you are only concerned about the pelvic dilatation, the likelihood of a good outcome is very high. Even the worse case scenario isn t horrific. As long as they don t tell you that you have low fluid, it should not affect your pregnancy in any way. However, a thorough anomaly scan is a must. This is because, as an isolated finding it probably has no significance, but this is considered a soft marker for Down s Syndrome. The correlation between an isolated finding and Down s, however, is very very weak, so if all other markers were checked, the likeilihood that the baby does not have Down s is very very high. Serial monitoring with regular ultrasound scans will tell you the prognosis and which way the lesion is going. All the best. Take care.