Can Catholics Have Sex While Pregnant?
In general, yes, it is morally permissible for Catholics to have sex while the wife is pregnant. There are, however, exceptions and certain considerations that have to be made.
Pius XI on the Greatness of Marriage
How great a boon of God this is, and how great a blessing of matrimony is clear from a consideration of man's dignity and of his sublime end. For man surpasses all other visible creatures by the superiority of his rational nature alone.