Everyone have different beliefs, and conditions. To me I will prefer the marriage before pregnancy, because pregnancy before marriage is against my belief though it is the same in some other traditions. Should in case you are doubting the lady you want to marry, I will advise you both go for some medical diagnosis, where you can speak to a medical practitioner, and they will direct you on the best diagnosis to perform.
I will say marriage before pregnancy is still very possible, the pregnancy before marriage was common in the ancient area, but not anymore, though some people still insist, with the healthcare system that can be taken care of.
Yes, everyone has their own traditions and beliefs. Although their are some of the traditional gifts that both parents must get know them before they agree to marriage, I don't believe that's still the case today. Although some people still engage in the behavior, it has decreased: As you mentioned earlier, new medical technology has made it easier by directing us to medical diagnostics to take the test that will show us each person's position and whereabouts. This is because some traditions bring up the idea only to see if she are capable of conception from the person she wants to marry.