AceShowbiz - Chrissy Teigen has let it slip her third child will be another little boy in an Instagram Story video.

The social media regular was updating fans on her pregnancy on Thursday, September 17 when she inadvertently called her unborn baby "he".

Grousing about the strains of her difficult third pregnancy she started the chat by saying, "My placenta sucks. It's always been kind of the bad part of my pregnancies. With (daughter) Luna, with (son) Miles, it just stopped taking care of him (sic)... I was getting huge, but he wasn't getting big at all."

"The baby is really, really healthy. He's big... oops!".

Teigen continued, "I'm stupid. Anyway... So it's growing beautifully. I'm feeling really good but my placenta's really, really weak, and it's causing me to really bleed a lot. So basically, it's just pretty high risk... (and) this poor thing has been through so much already."

"We just have to get my placenta healthy again, and that means not moving. So I'm (on) complete and total - don't get out, except to pee-pee - bed rest (sic). It's such a bummer because I had to cancel so much work, and I was so excited to talk to so many different people and do these events, because it would start to feel like normal life again. The timing is just s**t. I apologise, but I have to make baby OK, so there you go. Thank you for all your well-wishes."

Realising she'd revealed the sex of her baby, Teigen, who is married to singer John Legend, captioned the video: "hahahaha might as well tell you."