This is a fairly frequent finding on an ultrasound scan. Much depends on the grading of the swelling in the kidney. In any case, nothing needs to be done just yet. You should allow the pregnancy to proceed to term. After the baby is born, possibly on the 2nd day after birth, an ultrasound of the baby would be done to re-evaluate the swelling. Further tests may be necessary after that. In a majority of cases the swelling either resolves or stabilises without need for any treatment. In case a specific cause is identified, such as obstruction or reflux, appropriate treatment would have to be advised.