It depends on how long it has been since the medical error in question occurred. If you do not discover your injury caused by your healthcare provider's negligence until months or even years after the incident, the statute of limitations would not begin until your discovery date. However, you can expect the defense to argue you reasonably should have discovered your injuries sooner.
This may be their strongest attempt at getting your case dismissed. However, with the discovery rule in place, the statute of limitations will be temporarily told before beginning once you discover your injuries. Then, you will have up to two years to file a suit before you are prohibited from having your case heard by the Pittsburgh civil court system.