Are there any legislated supplications for the fetus in its early formative stages?

There is no specific du'a (supplication) authentically transmitted for the fetus. However, it is permissible to supplicate for it with general prayers for the righteousness of offspring, such as: "Our Lord, grant us from our spouses and our offspring comfort to our eyes and make us leaders for the righteous" and "And I seek refuge for her in You and her descendants from Satan, the expelled."