During your second trimester (weeks 13-26) anatomical ultrasound, you may be told your baby has Pyelectasis which simply means there is some extra urine accumulating in one or both of its kidneys.
It is seen more often in male fetuses. Your baby’s kidneys produce urine just like yours, which then flows down to its bladder. Due to pregnancy hormones, the flow can often be slowed down and the urine may build up in the kidneys causing this ultrasound finding. Uncommonly, there may be a true structural blockage causing this, which may need surgical correction after birth.
Pyelectasis is also seen by some as a soft marker for Down syndrome. A soft marker is something which may be seen at the time of the 18-22 week scan which may indicate an increased chance that your baby has Down’s syndrome or another chromosome anomaly but which in itself is probably of little or no significance.
Many medical providers will use a 4 mm size cutoff in order for it to be considered true Pyelectasis. A follow up Ultrasound is then usually done in the beginning of the third trimester to see if the issue has resolved. A cutoff of 6 to 8 mm in then usually used.
It is reassuring to know that even if the Pyelectasis has not resolved by then, it usually will after birth when the pregnancy hormones have left your baby’s body. An ultrasound is usually performed on your baby after birth if the Pyelectasis is still seen in the third trimester.