A marriage based on mutual understanding, love and respect can last for a long time. A child born in that environment will have a greater chance of being healthy and happy.
If you decide to have a child, it should be only after you both have figured your own relationship out. It takes time and effort, and you need to give that to yourselves.
Marriage, in some cases, is just not between individuals, but between families. A newly married bride will have to adjust to her new house, in-laws, husband’s nature and a whole lot of other things. It is not fair to burden her with a baby during that learning and transition period.
The time between the newly married couple is precious. You can have so much fun just being with each other and doing things together. This is the time to build your relationship, time when you should travel, explore new hobbies, time to finish that degree or study that course which will help you in your career, time to focus wholly on your career and build yourself up, time to put away that nest egg for a special occasion.
Having a baby will change absolutely everything about your life. You will have a tiny little soul who is totally dependent upon you for everything. You won’t be able to leave her and go anywhere much. You won’t want to.
With a new baby in your house, your sex life will change. Your wife will be more of a mother than a wife for at least some time. Both of you should be mature enough to handle these changes that a baby will bring into your life.
Discuss contraception with your fiancée even before marriage, or if that is not possible, you take up the responsibility and get contraceptives that you can use.
I would strongly suggest that you wait at least 3 years before having your first child. It will be beneficial for both of you, and the baby.