Is the Hadith whose text is: "Whoever among you strives her utmost to be a righteous wife, her reward is equivalent to that of one who fasts by day and prays by night" authentic?

The Hadith you inquired about, "Are none of you pleased that when she is pregnant by her husband, and he is pleased with her, she will have a reward like that of the one who fasts, prays, and strives in the way of Allah?", is a fabricated Hadith (Mawdu'). Al-Albani stated that its defect lies with Amr ibn Sa'id al-Khawlani, who narrated fabricated reports. And the Hadith, "When a woman becomes pregnant, she has the reward of one who fasts, prays, is devout, humble, and strives in the way of Allah," is also a rejected (Munkar) and fabricated Hadith. What Imam Ahmad narrated suffices: "If a woman prays her five (daily prayers), fasts her month (Ramadan), guards her chastity, and obeys her husband, it will be said to her: Enter Paradise from whichever of its gates you wish," and this is an authentic Hadith.