Lifestyle Health Jillian Michaels Reveals Her Fiancée Heidi Had Mild Postpartum Depression: 'I Didn't Know How to Help Her' "I don't think they realize that it can come in so many different shapes and forms," fitness guru and author Jillian Michaels tells PEOPLE By Julie Jordan Published on December 29, 2016 06:00 PM Share Tweet Pin Email Photo: David Livingston/Getty Images Jillian Michaels is opening up about the challenges she and fiancée Heidi Rhoades faced after the latter gave birth to their little boy. “The fourth-trimester stuff is so important because I wasn’t able to recognize that she had a certain amount of postpartum,” the 42-year-old fitness guru, who just released her new book Yeah Baby!: The Modern Mama’s Guide to Mastering Pregnancy, Having a Healthy Baby, and Bouncing Back Better Than Ever, tells PEOPLE. “I didn’t know what was wrong, I didn’t know how to help her,” she adds. Writing the book allowed Michaels to share their journey. “I think just being able to say, ‘Hey, this is what was going on with Heidi.’ Boy, do I wish I had known then.” Though the couple’s son Phoenix is now 4½, and their daughter Lukensia, whom they adopted the same month, is 6½, Michaels recalls the adjustment to becoming parents like it was yesterday. “While everybody goes, ‘Oh yeah, postpartum, I’m so scared of it,’ I don’t think they realize that it can come in so many different shapes and forms,” she says. “I don’t think they realize how their significant other might be feeling on both ends.” “Peppering in our personal experiences was actually really important because it was a way we could bring light to a certain issue,” she adds. “And I’m hoping it’s very relatable and nonjudgmental.” Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter. https://www.instagram.com/p/BMl-1BKBsxH/ Michaels says “everything that went on during Heidi’s pregnancy” was her inspiration to pen Yeah Baby!, including how “shocked” she was by it all. And true to herself, she wanted to write something that would give moms-to-be a straightforward, no-nonsense take. “The truth of the matter is as much as it’s like, ‘Oh, you’re pregnant!’, it’s dangerous and you’re not doing anyone any favors by not telling the truth,” explains Michaels, who also has training programs available on Fit Fusion. “I think the key is to tell the truth, but don’t judge.” “The reality is autism is on the rise, childhood cancer is on the rise, breast cancer, ovarian cancer, prostate cancer are all on the rise. Why do we think this is? C’mon,” she adds. “It’s all on the rise — learning disabilities — so you really do need to be mindful.” “It’s not just [fear-mongering]. The reality is that the world is a very scary place right now and the best way to combat that is by having the tools and the information. That’s how you have peace of mind.” RELATED VIDEO: Jillian Michaels Has Workout Tips For Parents This 2016 The former Biggest Loser coach admits she is no expert when it comes to parenting, and that her advice comes from a place of simply being deliberate about your health — specifically when you’re expecting. “It’s not about going, ‘Listen, you’re a s—ty mom,’ because God knows we all do the best that we can do,” she says. “The key is to meet people where they’re at — give them the tools and bring them along from a very nonjudgmental place. And I’m certainly the last person that would ever pass judgment. You can’t throw stones from your glass house; I am far from a perfect parent.” Michaels’ own experiences with Rhoades’s pregnancy inspired her to focus some of her concepts on things that could be going on outside of the strictly baby-related tasks new parents face. “I just know how disruptive a child is to a relationship because Heidi and I went through it,” she says. “And people don’t talk about that. I think the one [who] doesn’t carry the child doesn’t know what to do, feels helpless, feels displaced. And then I think the one who is carrying the child feels lonely, isolated, especially after the baby.” A perfect day at home with their two kids is now all about being active outdoors — and a little good-natured teasing. “We have horses and we live on a ranch/farm, so generally it involves family trail rides,” she says. “We’re really lucky to live in a really nice area, so we have lunch by the beach.” “It’s usually just crazy family time and we’ll go to this local playground and play [Teenage Mutant]Ninja Turtles and sword fight with my son,” Michaels adds. “My daughter and Heidi hate us both and think we’re crazy because we torture them all day long, which is so much fun.” For more from Jillian Michaels, pick up the latest issue of PEOPLE, on newsstands Friday.