Is there any evidence that it is Makrouh for the husband to look at the private part of his wife when trying to conceive a child? If so, is that the case even in general sexual acts? What is the reason for it being Makrouh?
Every Makrouh is harmful but not Haraam. Allah knows the details of the harm which might be unknown to us.
We have Hadeeths from the Prophet (SAWA) stating that it is Makrouh. It is not only when trying to conceive a child but it is Makrouh in any sexual intercourse.
Wassalam.