The HGTV stars opened up to PEOPLE about the joy of growing their family after a harrowing health battle

Erin and Ben Napier are thrilled to be expecting their second child, but parenthood wasn't always a certain future for the pair.

"We're very, very blessed," Erin, who will welcome a baby girl in May with her husband of 12 years, tells PEOPLE in one of this week's cover stories. "I think it's really wonderful to have a sibling if it's possible. And we didn't know if it was possible."

Listen to more of PEOPLE's exclusive interview with Erin and Ben Napier below on our daily podcast PEOPLE Every Day.

The stars of HGTV's Home Town already share daughter Helen, 3, but before getting pregnant for the first time in 2017, they weren't sure they'd be able to start a family. For ten years, Erin, 35, battled a mystery illness that turned out to be a perforated appendix. After a surgery to repair the issue in 2014, doctors told her that the damage left behind might make it difficult for her to have a baby.

"I was really, really scared. They said I could likely get pregnant but told me it could be difficult to carry a baby full-term," she explains. "I was terrified to even try, because what if I can't, and then I'm just devastated? What if we try, and something awful happens and it's this tragic loss for us?"

ben and erin napier
Credit: Brooke Davis-Jefcoat

The college sweethearts, who married in 2008, found out Erin was pregnant with Helen on Mother's Day 2017 but were hesitant to celebrate or share the news too soon because of potential complications.

Watch the full episode of People Cover Story: Ben and Erin Napier on or on the PeopleTV app.

"When it happened with Helen, I felt incredibly relieved with that first step: 'Well, I am pregnant. It doesn't mean that I will have a baby.' You have to accept that part of it when you have some strange health issues," she says. "It's an incredibly sensitive process—that's why we kept it a secret forever. Literally, tomorrow wasn't promised, and it felt best not to make a fuss. It's such a tender subject."

ben and erin napier
Credit: Larsen & Talbert

Helen's arrival, three weeks early but in perfect health, in January 2018, had left Ben and Erin feeling more optimistic. "I'm less nervous now," she says. "I know what to expect and they say no two babies are the same, but boy, I hope they are."

"Helen was a dream," Ben adds.

Last spring, an unusual event inspired the couple to start talking about trying for number two.

"My grandmother passed away in May. At the funeral, my dad and his only brother stood over her casket, and it just made me think about how important a sibling bond is and how we wanted that for Helen," Erin says. "We want her to have somebody to share her life with."

Erin and Ben Napier family photo
Credit: Brooke Davis-Jefcoat

They knew a pregnancy still wouldn't be risk-free, and things were more nervwracking for the couple thanks to the ongoing COVID-19 pandemic and a hectic filming schedule.

Thankfully, at 33 weeks mom and baby are both healthy. But Erin's baby bump is still barely noticeable, possibly a lingering effect of her surgery.

"When I had a perforated appendix, I got lots of scar tissue on my organs, and it's possible that's why I don't show," she explains.

Adds Ben, "The baby's, like, up in her ribs and lungs."

And while the situation is a little unusual, it doesn't seem to be causing any serious issues. "Everyone's very confounded by it. But the baby is measuring in the 65th percentile, so she's big, wherever she is," says Erin. "All is well."