Responses
The conclusion in an article said: Intercourse during pregnancy decreases. Important factors like culture, inadequate knowledge and excessive anxiety marked reduction in Chinese couples.
So, maybe this "Do not have sexual intercourse in the first three months" is a culture, like something the general public believed. Thus, it appears in several Chinese stories as the authors might be among the people that believed this general knowledge.
Sexual intercourse does not harm a pregnant woman or the baby she is carrying. It always amazes me how little information and knowledge Chinese manga authors have to make up stuff likes this to get content. I always get a little bored when the same plot happens in a lot of Chinese manga's. Always a female with a child, or pregnant, either loses the baby or keep it, finds out that they are from a wealthy family and wants some of it, and revenge and death and all that. It gets a little boring over time but I always come back for a good laugh with how bad the plot sometimes is. It's hilarious