I'm 36 weeks pregnant with fetal bilateral hydronephrosis, do ihave to undergo a c-section asap?

See Pedi Urologist: Bilat hydronephrosis can indicate several different problems. You should involve a pediatric urologist promptly. In the male fetus, this can indicate posterior urethral valves which needs to be addressed immediately upon delivery. It could also indicate bilateral vesico-ureteral reflux or obstruction where the kidneys drain into the ureters (upj-obstruction) either way, see peds uro stat.

CS most likely NO: Most babies with prenatally diagnosed bilateral hydronephrosis can undergo vaginal delivery. Hydronephrotic fetal kidneys do not burst at vaginal delivery, nor do they enlarge baby's abdomen too much. Hope you have/will see a pediatric urologist asap who willwork together with OB dr. Baby best delivered at tertiary care if hydronephrosis severe & requires early intervention. Induction > c-section.