Merchant told Pinkvilla that the baby wasn't planned and hence she was surprised when she tested positive.
"It came as a shocker for us initially as we weren't expecting it at all. We hadn't planned it. It was like a big shocker in the beginning but it gradually turned into a pleasant surprise," she said.
The couple is expecting their first child in August.
Have conceived naturally at 40: Merchant
The mother-to-be firmly believes that one needs to break societal norms, as she is doing.
"I have conceived naturally at 40 and I don't think that age is a major problem in today's era in terms of conceiving. Nobody can say that in my case I mean, as I said I conceived naturally at 40 and I think it's fantastic," she said.
You can see the baby announcement here
Rai wants a boy, his wife a girl
The couple confessed that they can hardly wait for the new member's arrival.
"Well, we want a healthy baby but if I have to make a choice then I am slightly vouching for a boy. Also because I really will get him to play cricket and do those things that I missed out on as a child," Rai said.
But Merchant wants a girl.
Several celebrities embraced motherhood after 35
Merchant is not the only one who conceived post the assumed "fixed age."
In 2016, singer Raageshwari Loomba gave birth to a baby girl. She was 41 at the time.
Director Farah Khan had welcomed triplets at the age of 43, through the IVF process. Actress Aishwarya Rai Bachchan became a mother to daughter Aaradhya Bachchan at the age of 38.