All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
First of all, you should know that pregnant women experience particular moods that we should consider. Modern medicine has proven that the pregnant woman experiences hormonal disorders which considerably influence her psychology and behavior, particularly during the last months of pregnancy. She suffers severe stresses and depression. Thus, she is in a dire need for relaxation, calmness, as well as psychological and physical rest.
Consequently, it is your duty to compliment her, show love to her and be close to her even if you do not like that. By doing so, you help her and protect her baby since many women might miscarry their child due to psychological disorders and not fulfilling their wishes.
You should also know that lying is prohibited in principle and it is impermissible unless it brings about benefit or wards off harm without which they cannot be realized. Consequently, when one wants to conceal something, it will be better to use figurative or indirect words. He can use words with double meaning of which he means one of them.
Finally, you should know that it is impermissible for you to respond to such a woman and stop helping your parents.
Allaah Knows best.