What could delay family reunification to Germany?

pregnancy is not a factor. But they always want to scrutinize that one is legitimatley married; voluntarily and of legal age. And they look at the finances, if one has a criminal record, and usually a spouse needs an A1 level of German  - althught there can be exceptions. Best to ask the officials in charge of your case.

If one is legally in Germany then the government is not going to say if they can have children or not. In some countries such a thing might be an issue if one comes temporarily and gives birth - if the child would then be given citizenship. But that is NOT how it works in Germany. A child born in Germany to non-German parents is not given German citizenship. This can only be given if the parents have continously and legally lived the last 8 years in Germany with unrestricted residency.