not to mention the fact that you need a univercity and nursery up ASAP.
and don't try to build anything else untill your basic colonist-needs structures are up and running.. Medical centers, agridomes, nurserys, and univercities. These four structures help you survive and without the last 3 listed you eventially loose the game.
Note: you only need 1 nersery and 1 university in game.
Yea, you need a nursery for population growth (no children will be born without a running nursery) and you need a university to get new workers (and scientists, of course). In some games you may have to research nurseries with Offspring Enhancement and universities with Research Training Program, first. As soon as these topics are researched (either by you or by game start) you will get a morale penalty if nursery or university are not operational.
Medical centers are not at all required to win the game and in some cases (e.g. in short games) they even make your life a little harder, because they require workers and scientists. They will, however, increase population growth and thus pay off in the long run. Hooman made some calculations on this, somewhere on the forum.
So, if you don't want medical centers, don't research them (the topic is Health Maintenance). If you research them, you'll get a morale penalty if the demand is above 100% (similar to residences). Beware that in some games you'll start with medical centers already researched.