'Dancing With the Stars' contestant Sasha Pieterse talks health scare and weight loss

The "Pretty Little Liars" star speaks candidly about her battle with polycystic ovary syndrome and the hardships she endured when it caused her to gain 70 pounds over two years.
4:37 | 09/28/17

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Transcript for 'Dancing With the Stars' contestant Sasha Pieterse talks health scare and weight loss
We move on to "Gma" cover story the secret health battle for pretty little liars star Sasha Peterson. We have her story. Reporter: Best known for her role on pretty little liar. If we get arrested what's going to happen to the baby. Reporter: Now she's heating up the dance floor on "Dancing with the stars." She's opening up about her very public 70 pound weight gain and it's emotional toll. When your confidence starts lacking and you get into a dark place it's Ike you don't love yourself anymore. It sucks. Reporter: She says haters on-line were vicious attacking her for the rapid changes to her body. They were like maybe she's pregnant. Then it turned into stop eating donuts. Reporter: Leaving her confused and frustrated she went in search for an answer. I went to a bunch of different doctors and they basically told me you'll level out. I ended up gaining over 70 pounds. I have finally was like this is not Normal. Reporter: Sasha said she was diagnosed with poly cystic oefry syndrome affecting one in ten women of child bearing age. I have a treatment plan. It's helped my soul because I'm back to me again. Reporter: Dancing is helping her to lose weight, but also gain confidence. Have you seen any weight loss since you started? I've lost 20 pounds now. To be able to wake up and be like I'm ready to go it's amazing. Are you in it to win it. 100%. That mirror ball is going to be mine. You go Sasha and thank you Abby. We're joined by Dr. Jennifer Ashton. You know about this condition all too well. How many patients come and see you? Literally on the daily basis. It's the most common and least understood condition. It's not a disease. It's a syndrome. There's no one test for it. It's an over activity of the oefryes. You can think of a penguin one at a time jumping off the iceberg. In pcos all those penguins are jumping together. Your oefryes are producing a lot more hormones. What are the symptoms? The main stay is irregular menstrual cycles. You can have excessive body hair, severe acne on the back or chest. Elevated test tos Roen and ultrasound findings. Usually you can make this diagnosis really talking to the person. We heard also weight gain can be part of it. This affects a lot of teens. What should parents know? Making the diagnosis in a teen can be harder. After a year and a teenager has this acne. Educate us right now. You have some food here. Nutrition is a factor. This can lead to other conditions. Exactly. Nutritional support is a main stay. I think it's well-known if you lose 5% of your body weight if you're overweight that can produce the signs and symptoms. Lean protein, good carbs and working with a physician who knows how diet and hormones interact can make a world of difference. It's about managing pcos. Sasha for being open about it in discussing it. 100%. The exercise has been huge for her. You can see Sasha on "Dancing with the stars" Monday night 8:00 P.M. Earn on ABC. Go outside to rob.

This transcript has been automatically generated and may not be 100% accurate.

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