What is the ruling on praying the obligatory and supererogatory prayers while sitting, with or without an excuse? And is it considered an excuse if done out of concern for the pregnancy?

Standing is a pillar of the obligatory prayer for those who are able, based on the Almighty’s saying: (And stand before Allah, devoutly obedient). If a worshipper is unable to stand due to illness or similar reasons, it is permissible for him to pray sitting or in a posture that suits his condition.

As for supererogatory (nafl) prayers, it is permissible to pray sitting even if one is able to stand, however, the reward for one who stands is double the reward of one who sits, if there is no excuse, based on the hadith: "The prayer of a man sitting is half the prayer."

What was mentioned about doing so (sitting) out of a desire for pregnancy is not considered a valid excuse permitting one to sit and abandon standing.