Having a set of twins is purely luck you can never plan to have twins. The chance of having twins is there but like i said its a chance. there is no clear percentage or ratio or a certain way that will grantee you will have twins. Twins will just happen and what you ll get its a surprise to. You might two boys or two girls or a boy and a girl. the type of twin is also a surprise you might get fraternal or identical twins. Fraternal twins are two twins who came from two different fertilized eggs. Identical twins are from one fertilized egg that split into two embryos.
Twins can be a big strain. You might be planning to have only a single baby and not twins. Now you have to go buy one more of everything and the cost doubles for everything now to. Now you have to buy two of everything your going to need for the baby and that can have a big strain on you. Unless you were ready for whatever happens. Then having a twins might be a gift now or mabey they were so pot to have twins no matter what i see as having twins a gift something that was meant to be.