Mila Kunis takes a maternity yoga class on her 31st birthday Credit: Interstar/MRM/

Happy birthday! Pregnant Mila Kunis celebrated her 31st birthday with a maternity yoga class on Thursday, Aug. 14.

Wearing a black form-fitting tank and black spandex shorts, Ashton Kutcher's fiancée's growing baby bump was on full display as she exited the pregnancy-friendly workout class in Los Angeles. The Jupiter Ascending actress carried with her a sweet bouquet of birthday flowers.

Although Kunis has stayed fit throughout her pregnancy, the That '70s Show alum admitted to Marie Claire she's thoroughly enjoying having larger breasts. "They're amazing!" she said of her boobs. "They've tripled in size. I was a 34A; now I'm a 36C. I'm so excited! I'm telling everyone I know, 'Go ahead, touch them!'"

The glowing star also told the mag she loves being pregnant. "Without being an a--hole," Kunis said, "I have to say, I love being pregnant."

Us Weekly confirmed the couple were expecting back in March. At the time, an insider told Us: "They are both so happy."