Usually, there are no problems with pregnancy and delivery per vias naturales in females with IS (operated or not). In my 42-year experience with scoliosis surgery I have never had negative experience with similar patients. Indications for cesarean section are to be considered in patients with an extreme pelvis tilt or increased pelvis inclination secondary to major lumbar scoliosis (usually neuromuscular not idiopathic genesis).
In my 30 years experience with 200 scoliosis surgery by year, I have the same opinion of Dr Tanchev, but some cases increase the curve after (of during) the pregnancy
normally not an issue at all but you may consider referring to anaesthesia regarding planning of epidural. If there is an extreme scoliosis it may cause respiratory concerns - one patient required oxygen then CPAP to get her to near term safely.
In my experience pregnant women with IS there is no problem for the vaginal delivery unless it has affected the pelvis and there is abormality in pelvis.with extreme scoliasis the Anaesthesia opinion we take as if LSCS requires.we have delivered patients normally via per vaginal route.thanks