A 75mg dose is highly unsafe (estrogenic) even for a non-pregnant woman and I would absolutely not even try that when pregnant. Unless the doctor says otherwise, I would not use more than 5mg while pregnant and always take it with progesterone. Btw, those fertility studies rarely used more than 25mg and some of them used as little as 3mg daily. Not sure where you saw reports on women taking 75mg for fertility but if they do then it is likely to have an opposite effect at that dose. Animal studies show that anything more than 15mg human equivalent dose of DHEA raise prolactin, and high prolactin is a major cause of infertility in women.
Honestly I just googled "dhea mg fertility" and scrolling through the results saw 75mg, 25mg 3x per day, and even 100mg. Although I admit, I didn't open up the articles to read them thoroughly.
Yes, I believe my progesterone quantity greatly outweighed my dhea. 100mg dhea dissolved in 34ml progest-e. Plus I take pregnenolone.