Is my obligatory prayer, performed while sitting due to back pain in the sixth month of pregnancy, religiously acceptable, even though I am able to perform it standing?

Standing in an obligatory prayer is a fard (religious duty). If one prays sitting without a valid shar'i (Islamic legal) excuse, her prayer is not valid and she must repeat it. However, if there is extreme hardship or fear of increased illness, she is permitted to pray sitting, and her prayer is valid, and she will receive the reward of one who prays standing, because extreme hardship is a religiously recognized excuse.