How exciting! As someone who has lived in seven countries, one of them twice, in the last thirty years, I envy you, I have only been able to visit China once, but It is fascinating. This will be a wonderful opportunity for your kids. In my experience as a foreign service wife, countries like China take great pride in the medical care that they provide to foreigners. Your husband’s company should be able to provide you with information about the local health care. If you are really worried, you could possibly make arrangements for a little trip to Hawaii, and have the baby there.
Join the American Women’s Club as soon as you get there. The expat community will be very accepting, and people make an effort to help newcomers. It is not like moving to a new city at home. The American Women’s Club will have information about doctors, dentists, which are the best stores to get what you need, everything that you will need to know. They will most likely have a class in survival Chinese, but I bet that you can get away without it, although speaking the language would make your time there more interesting. As a busy mother of a family, you most likely will not have the time to learn a language like that. English is widely spoken in large Chinese cities at least in the areas where you will be going. (My brother-in-law is a professor of English literature in a major Chinese university.) You are not likely to be socializing with many ordinary Chinese anyway. We have lived in both Russia and Cuba, and of the Chinese government is anything like the Russians and the Cubans, ordinary Chinese will be discouraged from having anything but business relationships with you. You won’t lack for a social life though, the expat community will be very active. The American Women’s Club will probably even have a group for new moms. There will be lots of activites for the kids, too.
I do not have information about Mass in Shanghai, but I know that Mass offered by a real Catholic priest is available in Bejing. You will probably be able to find it in Shanghai, too. As long as only expats attend these Masses, and they don’t engage in proselytizing, the government probably looks the other way. Since Catholics do need to be careful about this any one with information about Mass in Shanghai will PM you.
I hope that you will take advantage of this wonderful, once in a lifetime, opportunity. We are all waiting to hear what you decide.