Medical services — always there for that “just in case”.
On most regular railway trains, medical services are available. These are in particular part of a long-distance journey (over around a thousand kilometres or so).
In general, ask train crew for detailed information about where to find these services. Whilst they can’t undertake major operations, basic services, such as probably a band-aid, should be available.
Are you a licensed medical professional and do you speak Chinese? Being a Good Samaritan isn’t just a “Western thing” any more. If you can help in the event of emergencies, please tell a member of the train crew (ideally, also tell them where you’re leaving). Thank you for saving lives on the railways.
Expecting a newborn? In many cases, Chinese Railways have successfully “given birth” to new babies onboard. This is most likely less about trains spawning newborns and much more the case that medical professionals helped out! If you’re a mother-to-be and are expecting your baby boy / girl, chances are, even if you’re stuck on a train, help should be at hand.