Is it permissible to resort to IVF after two years of trying to conceive, especially with a slight problem in the husband's sperm viscosity and the wife's age being 33.5 years?

The sister asking the question believes she can conceive naturally despite her husband's condition, citing her first pregnancy as proof. She described her husband's problem as minor. Therefore, we do not see it permissible for her to resort to IVF due to the reservations associated with it.