Six weeks after delivering her first child by cesarean, Lewek performed the Queen of the Night at the Met. (Morley sang the role of Pamina, the Queen’s daughter, having just given birth to her third, and the two singers spent their breaks breastfeeding in the same dressing room.) The week before rehearsals started, with her “entire support system slashed in half” by surgery, Lewek was still able to sing only up to a high G, a full octave below what Mozart’s music required.

With the help of a physical therapist, she devised a workaround. “I found a diaphragmatic rather than muscular way of supporting staccati in Queen of the Night,” she said, “that, overall, I would never want to sustain my entire singing career. But it got me through that gig and it opened up a new set of skills.” Her tone, too, opened up, after the births of each of her children, when she said she noticed “a blossoming of the tone quality of my voice that now has lent itself to bigger repertoire.”

She wondered: “Was it the pregnancies that really changed my voice, or was it the recovery?”

Lewek said she was fortunate that she was able to perform her star role in the “Magic Flute” up until being eight and a half months pregnant with her first child. But during that same pregnancy, she was abruptly removed from a different role, shortly after she had shown up to rehearsals with a visible baby bump. Citing safety concerns involving the set, the company urged her to withdraw, she said, even though she felt comfortable with what the production required of her. When the company added financial incentives and promises of a future role, she relented.

“It wasn’t my decision,” Lewek said, “but my agent said I should grab the offer and run.”

Morley said she lost a major role because of concerns she wouldn’t fit through a trap door in the set. And during a later pregnancy she lost a role because it required singing an aria standing on a chair in what would have been her second trimester. “I was really considering making a statement,” she said, “but these were companies I wanted to work with again, and I was very worried that there would be repercussions.” Besides, her contract was paid, which she knew was not always the case in such situations. “It felt kind of like dirty money,” she said. “Like they were paying me so I would not talk.”

One singer who went public was Julie Fuchs, after she was booted from a production of “The Magic Flute” two years ago at Hamburg State Opera, where she would have sung the role of Pamina four months into her first pregnancy. When Fuchs announced on social media that she was out of the production, her feed lit up with outrage. Many commentators suggested misogyny was to blame for the company’s decision, although the director, Jette Steckel, was a woman. After arbitration, Fuchs settled with the company under terms that do not allow her to speak about the case.