Hilary Duff Details 'Lightning Crotch' Pain During Her Pregnancy

Hilary Duff is being "struck by lightning" during her third pregnancy...but it's not what you think.

While appearing on Friday's episode of "The Ellen DeGeneres Show," the 33-year-old actress -- who is expecting her third child -- revealed she's been experiencing what is known as "lightning crotch."

"I didn't know about it. Let's be real here, I think Matt [Koma] was the first one to put me on blast with that and then I just happened to repost it because I can't help but think his trolling me is so funny," Duff told guest host Brooke Baldwin. "I didn't have it with my other kids, so I texted my midwife the other day and I was like, 'What's up with the stabbing pains in my vagina, I'm not feeling this.'"

"It feels awful, like you're being struck by lightning," Duff added. "And, [my midwife] just wrote back, 'Oh, lightning crotch,' like it was no big thing. I was like, 'This is quite traumatic.' It'll just strike and all of a sudden you're doubled over and then it's gone. So, the term is actually called 'lightning,' [meaning] the baby is getting ready for birth, like lowering so you can actually breathe and get a full supply of air in your lungs, which I haven't been able to do for months, but you get stabbing pains."

According to What To Expect, "lightning crotch" is "surprisingly common during late pregnancy" and can occur "without any warning." While it's nothing to be concerned about, the pain should only last a few seconds. If it's any longer, one should reach out to their doctor.

Despite the pain, Duff -- who said she's a "couple weeks" away from giving birth -- called baby No. 3. her "best pregnancy so far."

"I shot a season of the show ['Younger'] and we were in New York, just busy with the other kids and their lives," the "Lizzie McGuire" alum explained. "I think that's helpful because I don't have as much time to focus on every ache and pain or everything that happens, like, 'the baby is the size of this fruit this week' or whatever."

Unlike when she was pregnant with Banks, now 2, and Luca, now, 8, Duff said she doesn't know the gender of her third child, shutting down fan speculation that her blue hair meant that she was having a boy.

"I don't know why I have blue hair, other than I was just like ready to have fun. I'm feeling a very blue moment," she said, "but we don't know the gender of the baby."

"We found with Banks what we were having and I found out with Luca and we were just like, you know what? This has been a crazy year, let's do something even more crazy and not find out which baby we're having," she added. "We have one of each and I'm just really looking for that moment, either way we're going to be so stoked and so excited and I think it's going to be a giggle-fest of like, 'we thought it was this, but you were this!' or 'Oh my god, we were right, it was this!'"

Duff's new addition will be her third child and second with her husband Matthew Koma. She shares Luca with her ex-husband Mike Comrie.