Selected By the Alien Scientist by Ashlyn Hawkes

She’s intelligent and skilled. So is he. Perhaps there are some skills aside from their minds that they can explore.
Johanna Oldenberg is a scientist, working to ensure that the Novans and their chosen female cohorts can produce children. Scientifically, it should work, and it soon does for Lisa and her alien lover, Commander Brax. All of the other couples, though, are failing.
Pressure is mounting to find a solution. Otherwise, the Novans will die out.
Soon, they make a breakthrough. It seems the secret might lie in a woman’s pleasure, and one of the alien scientists is more than willing to test that theory on Johanna…