Shay Mitchell opens up about pre-partum 'severe depression' at start of pregnancy

"Pretty Little Liars" star Shay Mitchell did not reveal her pregnancy publicly for nearly six months, a period of isolation that she said left her in a "severe depression."

"I think it's really interesting that pre-partum depression or feelings of isolation in pregnancy are not more vastly discussed," Mitchell, 32, said in a new interview with the maternity lifestyle brand Hatch. "Feeling that I was alone in my depression compounded my state of mind, but [I] have found since sharing the news publicly that many women feel as I did."

"Pregnancy can be a hard time, especially if you're having to hide it," she said. "After I came out publicly, I felt an enormous wave of relief and was finally able to start enjoying the pregnancy."

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Mitchell, 32, has said before that she kept her pregnancy quiet for so long because of a prior miscarriage.

The actress described experiencing depression at the start of her pregnancy as "a shock." Not telling anyone about her pregnancy, she said, left her with "crippling" depression and anxiety, feeling like she was "going out of my mind and questioned why nobody ever talked to me about this phase."

Moms in the U.S. typically announce their pregnancies once they are safely past 12 weeks, or the first trimester, a time when the embryo has become a fetus with its major organs and systems formed.

The first trimester can also be a time when women experience some of their worst pregnancy symptoms, meaning they are coping with both the emotional and physical challenges of being pregnant while also trying to hide it.

"I've had a lot of women talk about how long can they go with hiding their pregnancy and they feel like they have to keep their game face on," Lisan Martin, a Washington, D.C.-based therapist who specializes in infertility therapy, told "Good Morning America." "What makes It particularly hard is that being pregnant is supposed to be this amazing experience and you're supposed to feel so joyful but there's a lot going on."

"It's such a surprise for women to find that they can experience depression in the early months of pregnancy and it can be very isolating," she said.

Perinatal depression is an umbrella term for depression experienced by women during pregnancy and up to a year after delivery. The type of "pre-partum depression" Mitchell describes would be when symptoms appear anytime during pregnancy, according to Martin.

Despite major medical organizations recommending screening for perinatal depression over the past several years, half of all women in the U.S. remain undiagnosed and untreated, studies show.

Women can be helped though through counseling interventions, specifically cognitive behavioral therapy and interpersonal therapy, according to a report released earlier this year by the U.S. Preventive Services Task Force (USPSTF).

Mitchell, who is expecting a girl, did not reveal how or whether she was treated for her depression, but said since announcing her pregnancy, a community of women has lifted her up.

"I've been fortunate since sharing the news of my pregnancy to have some amazing conversations with other pregnant women and moms and know that all these feelings are 'normal,'" she said. "So now we just need to normalize them by discussing more openly."

A celebrity like Mitchell -- who started a YouTube channel about her pregnancy -- speaking out about loss and the ups and downs of pregnancy is exactly what is needed to let women know a wide range of emotions is normal, according to Martin.

"A burden shared is a burden cut in half," she said. "Sometimes when people are isolated and feel alone with either trying to process their pregnancy or a pregnancy loss, just to see a public person being open about it can be really normalizing and reassuring."

"I've been in practice 30 years and this is really different that women are so open," Martin added. "I think it's great that [Mitchell] is speaking out."