Sasha Pieterse gained 70 pounds when she was 17 years old amid her struggle with polycystic ovary syndrome (PCOS).

The 'Pretty Little Liars' star - who recently opened up about dealing with the hormone condition scene her teenage years, including during her time as Alison DiLaurentis on the hit show.

Appearing on 'The Squeeze' podcast, she said: "This is part of the health issues that I was speaking of while I was going through 'Pretty Little Liars'.

"So when I mean it was documented it was like, the changes that were happening to me were documented on camera."

The 27-year-old star explained that she "never had a regular period ever", and the advice from doctors didn't pan out.

She added: "I was just always told by gynaecologists that I was just young. Like, ‘Don't worry, it'll regulate.'"

However, it wasn't the case and she noticed other differences in her body with "no explanation".

She said: "When I turned, it was probably around 15-16, that I started noticing a difference in just my metabolism in general.

"At 17, I gained 70 pounds in the year, for no reason. There was no explanation for it."

Despite seeing "over 15 gynaecologists" - some of whom blamed Sasha herself for her weight gain - didn't feel like she was being taken seriously, and insisted on having her blood tested.

She continued: "It was the most frustrating experience and disheartening because no matter what I did, no matter how well I behave, no matter how great I treated my body, things were actually getting worse rather than better, it was very very confusing.

"So after a long process… someone recommended that I go to an endocrinologist."

Sasha was told she had PCOS and needed a blood test to confirm her diagnosis, and she wasn't previously aware of the condition.

She said: "I was like what's that? I'd never heard of PCOS before. And it's a disease, it's not curable, it can be dormant, that's—at this stage—that's what they know.

"And the most frustrating part about this is that it's fairly easy to diagnose. And really what it is, it's a hormone imbalance, it's a hormone disease and it's so easy to see because your testosterone or your oestrogen will be really high, you'll have really low vitamin D levels, you'll be deficient in a lot of things."