My son's kidneys had that too at an ultrasound around 26 weeks. One was 5.1 and the other a little less. It had completely corrected itself at the 32 week ultrasound, and I hope you have the same experience. For what it's worth, my midwife said ultrasound techs make a big deal out of every little thing because it's the most sued area of medicine and that in her 12 years of practicing, she's never seen anything come of pylectasis diagnosis.
I'm going through the same thing . Both my sons kidneys are bigger then they should be . I go in on Friday to see if they are getting better or worse . It's scary but my doctor keeps telling me no th worry.
My son had it we found it at a 26 week scAn! I decided to see a pediatric nephrologist while pregnant and he followed me through out my pregnancy and gave my dr protocol to follow up delivery when my son was born I took him to see the kidney dr and he was followed by him not his peditrician my son eventually need surgery cause the swelling didn't get better. My personal recommendation would be to get a lidney dr involved kidney problems can be nothing but can also be serious I live in ny so I can recommend dr if ur in area good luck n