There is no law that obliges you to inform your employer of your pregnancy by a certain deadline. Nevertheless, you should notify your employer in good time, as the employer can only fulfill its duty of care if it is informed of your pregnancy.
In particular, if there is a ban on work for pregnant women, the continued performance of the job may endanger or even harm the child. So if you work as a craftswoman, your employer may ask you if you are pregnant and you should answer truthfully.
Even if there is no deadline for reporting a pregnancy, we recommend that you inform your boss in good time for reasons of fairness.