We were on the cautious side, so did a health screen before marriage and conception, including blood, urine and stool test.
Blood test: can detect HIV, Hepatitis, blood group
If male blood group is +, female blood group is -, then chances are first baby would be ok, but second baby not.
If need hepatitis boost jab, can get it too.
female: if has no Rubella immunity, has to get immunized.
Guess the above are the more important ones for conception.