The concert didn’t sound unusual. The Choral Arts Society sang with its typical verve. The parade of soloists basked in the customary applause, and the orchestra played Beethoven’s “Missa Solemnis” with the radiance and rigor it requires.

But an unexpected presence — a large hump bulging out from the soprano’s amethyst gown — caused stirs in the Kennedy Center Concert Hall. Surprised audience members noted Erin Wall’s impending motherhood when she perched herself in front of the choir.

The pregnant opera singer isn’t an uncommon sight. Last month, Janai Brugger, 29, then 6¹ / ₂ months pregnant, made her Metropolitan Opera debut as Liu in Puccini’s “Turandot.” Costumes and characters can mask the evidence of pregnancy. Unsuspecting viewers would never notice the bump.

But at 32-weeks large, it was clear that Wall was singing for two. Breathing for two. Performing Missa Calisthenics too much, standing and sitting ad nauseam. Oh, the nausea!

“That part is difficult, the getting up and sitting down,” said Wall, a Toronto-based opera singer who performed with the National Symphony Orchestra last November. “It gets exhausting. I think I’d have rather just stood there the whole time.”

Pregnant opera singer Janai Bruger made her Metropolitan Opera debut as Liu in Puccini’s ‘Turandot.’ Costumes and characters can mask the evidence of pregnancy. Unsuspecting viewers would never notice the bump. (Kenneth Dolin)

For millennia, women have dealt with the ups and downs of pregnancy, whereby simple tasks — walking, eating, even breathing — become challenges. Singers, dancers and musicians have additional concerns: They must navigate this common stage of womanhood on stages, acting as though little is changing inside their expanding bodies. They know the perils of pregnancy, how the experience can disrupt careers. And as the public continues to debate Yahoo CEO’s Marissa Mayer’s two-week maternity leave and the needs of pregnant professionals, women artists have unique worries: Will my voice change in the second trimester? Will my dance partner be able to lift me? Can I still fly to concerts across the globe, and if so, who will carry my cello case?

“My first pregnancy, I didn’t know what to expect,” said Wall, 37, who gave birth to her second child last week. “I was scared that I wouldn’t be able to do my job. But once I learned how to cope with the sickness, it was fine.”

So expectant mothers adapt. They perform with precision, even as their instruments change. Dancers mourn the loss of muscle tone as it melts away like a Dali scene. Opera singers revel in the surge of hormones that give their voices richer, fuller timbre. Cellists lay their instruments on their bellies and hope the baby doesn’t kick when the timpanist strikes.

“My daughter would always react to something particularly loud,” said NSO principal second violinist Marissa Regni, 44, of her now 9-year-old daughter Sofie. “She’d also inevitably start kicking and poking right when I’d start a solo.”

Most artists mask discomfort with aplomb. They are trained, after all, to maintain graceful demeanors. But don’t think for a moment that pregnant performers aren’t preoccupied by nature: it’s calling them to the ladies’ room during intermissions.

Dancers suffer the most from pregnancy’s unforgiving elements: their prolonged breaks from work often begin well before they give birth. Xiao Nan Yu, 34, a dancer with the National Ballet of Canada, was preparing for the North American tour of “Alice’s Adventures in Wonderland” last year when she became pregnant with her second child. Unable to debut the role of the Queen of Hearts, she will perform it this month at the Kennedy Center almost one year after giving birth.

“You are so mentally aware that your body is changing, you worry about your heart rate, your breathing,” Yu said. “And the boys are just so scared. They don’t want to lift you. They don’t want to have anything to do with you.”

After her first pregnancy, it took Yu nearly a year to get back into shape. “My body forgot how to dance. I had to reteach myself the movements,” she said. But her second pregnancy was different: she was dancing two months after childbirth, a reminder that every pregnancy poses unique challenges.

Erin Du, 34, school director at the American Dance Institute, recalls having to drop out of a role because of pregnancy in 2007 when she danced with the Washington Ballet. Her center of gravity was off, and her muscles were tighter. During her first trimester, the mere sight of spinning dancers caused terrible dizziness.

“I was the first woman in the company to get pregnant,” Du recalled. “One of [the dancers] later said to me, ‘I always knew you were going to the bathroom to throw up when you’d pull your hair up as you walked by.’ ”

Du served as the company’s ballet mistress while pregnant, attending practices and learning roles instead of performing.

Until a couple of decades ago, dancing while pregnant — or returning to a company after pregnancy — was a rare occurrence. Women feared pregnancy would ruin their careers, and the stigma often caused women to delay motherhood or retire after giving birth. Now, dancing while pregnant is relatively common, with some ballet dancers performing into their second trimester. In 2004, Irina Dvorovenko, a principal dancer with the American Ballet Theatre, danced the pas de deux from “Swan Lake” when she was four months pregnant. However, most dancers stop performing in their first trimesters.

Opera singers sometimes forgo roles as well when visibly pregnant. Wall notes that a company asked her to drop out of a role over the summer because her character could not appear pregnant. (She declined to name the company or role.)

Some companies are more flexible, though, masking pregnancies with elaborate costumes. In July, Wall played the title role of the Santa Fe Opera’s production of Richard Strauss’s “Arabella.” She hid her pregnancy under a fur-trimmed coat and loose-fitting gowns with elaborate details.

Brugger also wore a loose-fitting costume while playing a slave girl in “Turandot.”

“Liu is a pregnant-friendly role,” she said. “Her costume isn’t tight or fancy. It was comfortable.”

Opera singers enjoy the benefits of hormonal changes more than other performers. Many singers find that their voices, both during and sometimes after giving birth, become stronger due to higher levels of progesterone, the hormone that regulates ovulation.

Stephanie Adrian, an opera singer and research affiliate of Emory University, published a case study in the Journal of Singing that chronicled her third pregnancy and its effects on her voice. She found that the timbre and warmth of her voice changed in the second trimester,

“I was surprised that vocal color is hormonally influenced,” Adrian said. “The same hormones that allow you to have a baby also affect other things within the body.”

Brugger felt the change in her second trimester, too: “My voice has gotten fuller and mature. It’s easier to sing through my middle voice.”

“The hormones seem to give an extra richness and womanliness,” Wall echoed. “It’s helped me with my middle and low range.”

Still, opera singers sometimes struggle in their first trimesters: morning sickness and acid reflux can cause extra problems for a singer’s vocal chords. And in the final months of pregnancy, when many women have difficulty breathing, opera singers have to learn different breathing techniques. Brugger worked with a coach to learn how to breathe “underneath her abdomen.”

“Breathing is the hardest part,” Wall said. “The baby is sharing so much oxygen, it’s harder to sing those really long phrases.”

While the hormonal benefits tend to disappear soon after childbirth, there are some lasting effects. Wall noted that during her first pregnancy, her rib cage expanded by four inches. Such growth might worry the typical size-conscious woman, but opera singers welcome the extra inches.

Soo-Kyung Hong, 34, the cellist of Trio con Brio, will not be performing at the Kennedy Center in March. She’ll be in Denmark, preparing to give birth to her first child as her husband, Jens Elvekjaer, the pianist in the trio, performs in Washington without her.

“Another cellist is taking my place,” Hong said. “It will be two weeks until my due date, and it is too much risk.”

So far, she has maintained her arduous performance schedule, but had to plan for the interruption. Hong says she and her husband put children off for years because their tour schedules, as many as 90 concerts each year, made it difficult to have a child.

And despite her “small stomach” in the first trimester, the pregnancy was already affecting Hong’s performances. During the Copenhagen Chamber Music Festival, the trio played Olivier Messiaen’s “Quartet for the End of Time,” a wrenching piece famous for where it was composed: in a German prison camp in 1941.

“I was so taken by the music, praising the eternity of Jesus Christ at the end of the world, that I just started sobbing during the piece,” Hong said. “It was this terrible five minutes. My eyes were running, my nose was running. I had to bury my head in my cello.”

It was the first time she had cried during a performance.

“Later, some people said, ‘It’s probably your hormones,’ ” Hong said, laughing.

Regni, too, had difficult performances. When she was eight months pregnant, she underestimated the strain of performing in the 100-degree heat and performed with the NSO for the annual Fourth of July concert on the National Mall.

“I couldn’t drink a lot of water, so I brought ice chips and freezer packs,” Regni said. “Every time the camera wasn’t on the orchestra I put them on my neck and face.”

Regni says her greatest surprise, one that many pregnant musicians note, is how her daughter responded to music in utero.

“She would react very violently to contemporary music,” Regni said, laughing.

But she took to certain instruments: “Every time the sax played, she’d stop kicking and I could feel her calm down.”

Time will tell whether her daughter truly has a love of the saxophone, but if Wall is any indication, tastes change after the womb.

“It’s funny, my mom is a cellist and she couldn’t play past seven months because I would kick the cello right off her stomach,” Wall said. “But the sound of the cello now — to me, it’s the best sound on Earth.”

National Ballet of Canada performs Christopher Wheeldon’s adaptation of Lewis Carroll’s children’s classic.

Jan. 18-Jan. 27 at the Kennedy Center. 202-467-4600.