Teigen and Legend have been married for almost 9 years and have two children, Luna and Miles.
The couple has previously said that their first 2 children were conceived through in vitro fertilization and in her announcement Wednesday, Teigen said the new baby is on the way “1 billion shots later.”
Teigan had been hesitant to announce the pregnancy, she said.
“Every appointment I’ve said to myself, ‘ok if it’s healthy today I’ll announce’ but then I breathe a sigh of relief to hear a heartbeat and decide I’m just too nervous still,” she wrote.
“OK phew,” she wrote, “it’s been very hard keeping this in for so long!”