WATCH AND LEARN: Teaching a recent master class at Princeton Dance and Theater Studio, New York City Ballet principal dancer Ashley Bouder urged students to stand behind more experienced dancers in their classes and learn by copying what they do. She is nearly six months pregnant with her first baby, due at the end of April.

At nearly six months into her pregnancy, Ashley Bouder’s ballerina silhouette is interrupted by a small, round bump. But the acclaimed New York City Ballet principal dancer, who taught a recent master class at Princeton Dance and Theater Studio, remains as lithe as ever.

The long neck, graceful arms, and razor-sharp, pointed feet were all in evidence as she led some 28 students through a full class that challenged them on several levels. Ms. Bouder, who is 32, mixed up timings and encouraged the aspiring dancers to “change it up a little.” When a group of less experienced students had trouble mastering a particularly tricky combination, she urged them to stand behind the older dancers and do what they do.

“That’s what I did when I got into the company,” she said of her early years at City Ballet, which she joined at 17. “I always stood in class behind Margaret Tracy and Miranda Weese, and just copied them,” she said of the former ballerinas. “That’s how you learn. You copy.”

Risa Kaplowitz, co-founder and director of the studio in Princeton Forrestal Village, invited Ms. Bouder to teach after seeing a post on Facebook saying she was available for teaching during the next few months. Arrangements were made, and 28 students quickly signed up for the two-hour session.

“The dancers absolutely loved her class, corrections, and advice,” Ms. Kaplowitz said. “The movement was faster than many typically do at this point in their training because Ashley was giving them all a taste of the Balanchine technique, which has generally sharper accents and quicker tempos than typical classical technique. The students enjoyed the challenge immensely.”

In a video about Ms. Bouder, CIty Ballet ballet master Peter Martins says that as a dancer, she reminds him “of nobody else.” Audiences relish her speed and fearless attack, which sometimes cause her to fall on stage. Her technical gifts are considerable. But she has worked hard to develop her softer, more lyrical side, required for such roles as Odette, the white swan, in Swan Lake.” She grew up in central Pennsylvania and was trained by Marcia Dale Weary, whose school has turned out numerous professionals with major ballet companies.

Despite Ms. Bouder’s busy City Ballet schedule of rehearsals and performances, her guest gigs with other companies around the world, and her pursuit of a degree in political science from Fordham University, she makes time to teach at the company’s training ground, the School of American Ballet, when a substitute is needed. She also teaches at Ballet Academy East and Manhattan Youth Ballet in New York City.

“I started teaching when I was 13 or 14,” she said during an interview after the Princeton class. “Marcia Dale Weary takes people who have an aptitude for teaching and starts them off teaching the youngest classes. I had a class on Saturday mornings of really little ones. Now, I prefer to teach older students. I like seeing them improve — seeing that light in their eyes when they get it, when they really understand.”

Times have changed since the days when George Balanchine, the famous choreographer who co-founded City Ballet and died in 1983, was running the company. Going to college, having babies, and doing guest appearances outside the troupe was generally frowned upon. “Balanchine wanted his ballerinas to be his,” Ms. Bouder said. “But the world has completely changed. You can’t run an arts organization like that anymore. A lot of us go to college, taking a few courses at a time. And these days, City Ballet goes above and beyond with maternity leave. They want you to look and feel your best, so they are very generous with time. And Peter Martins let me dance until I was showing too much.”

Ms. Bouder’s last performance was just a month or so ago, as the Sugar Plum Fairy in City Ballet’s production of The Nutcracker. She is planning to take just a few months off after the birth of her baby — a girl due April 30 — and be ready to dance with the company when they travel to Paris in the summer.

Like many of her colleagues, Ms. Bouder is active in social media and frequently tweets about her personal life. “It shows I’m a real person if I’m posting pictures of my dog or information about my pregnancy,” she said. “All of my shows when I was pregnant were sold out.” Her fiancé, who works in private equity, comes to her performances with a bouquet of flowers. When she debuted in the ballet La Sylphide a few months ago, he threw her a surprise party at the Tavern on the Green restaurant. “He’s the most supportive person I know,” she said, with a contented smile.

Following the class, and before taking selfies of themselves with Ms. Bouder, students crowded around her to ask questions. What is her favorite role? “The Firebird,” she said. “It has great make-up and hair.” What was your biggest obstacle? “When someone tells you you can’t do something, and you just have to do it,” she answered. Does she get nervous? “I try to make eye contact with other dancers,” she said. “I get energy from them and they get it from me, and that helps with nervousness.”

And finally: Why do you love to dance? “You can be your most free,” she answered. “There is nowhere on earth where you have that sense of freedom.”