How do I know if I should go to the hospital for contractions?

Discuss with OB. Decisions about when and where to be evaluated depend a lot on the history of the patient, any risk factors for bleeding, delivering early, problems with baby or mom, even bad weather. If contractions start, pregnant women can begin timing them and noting their strength and call the OB or physician on labor and delivery. If bleeding, preterm, high risk, etc., they can go to hospital by ambulance.
Call L&D. For typical term pregnancies when contractions are spaced every 3-5 minutes apart for an hour and do not go away with rest and hydration, that is when we advise you to go to the hospital. For preterm pregnancies or if you have complications such as placenta previa or bleeding you should go immediately. Call l&d or your doctor and they will help you decide when to go for your situation.
?? Labor. If you are not sure of what is going on, you should call your doctor or just go to labor and delivery at your hospital. It is always safer to be evaluated and find that everything is ok, than to wait until it is too late.
Contractions. Call your doctor asap to ask your question.