Five years ago, Erin and Marianne Krupa chose to start a family. They moved to Montclair, N.J., from a more conservative environment in North Carolina, and decided that Erin would carry their first child.

Erin Krupa remembered her fertility doctor looking her in the eye and promising to help her become pregnant.

But there were complications. At an appointment with her doctor in 2013, Ms. Krupa, then 33, learned that she had benign cysts on her uterus and Stage 3 endometriosis, in which the tissue that normally lines the inside of the uterus grows outside. That meant she was infertile.

Despite her doctor’s assurances that insurance would pay for fertility treatment, Ms. Krupa’s provider, Horizon Blue Cross Blue Shield, denied coverage. The company cited a state insurance mandate from 2001 that required most women under 35 — no matter their sexual orientation — to demonstrate their infertility through “two years of unprotected sexual intercourse.”