The "Almost Famous" star and her mother Goldie Hawn sat down for a joint chat with host Ellen DeGeneres this week, begs September 17, and in the episode, which airs on Thursday, September 20, she admitted she is due very soon.
"Let's just say you probably have never had anyone this pregnant on your show," she told the talk show host, who suggested she looked like she could go into labour "any minute now", to which Kate replied, "It could be - water could go any second."
She acknowledged the size of her baby bump, admitting that the child is going to be "pretty big."
The 39-year-old is expecting her first child with boyfriend Danny Fujikawa, and her third in total, following sons Ryder, 14, from her marriage to Chris Robinson, and Bing, seven, from her relationship with Muse's Matthew Bellamy.
Kate and Danny already know they are expecting a girl and have got "a couple of" names they like, but won't make a final decision until "the day comes."
That will help Goldie, who accidentally knitted a pink blanket when Kate was in labour with Bing.
"I thought that the last baby was going to be a girl, so much that I did knit a pink blanket," she explained. "And when I saw his penis coming out, I, like, rack focused (switched focus) to the pink blanket and thought, 'Boy, did I screw up!'"
The veteran actress recalled how last time Kate was in the hospital preparing to give birth, she got hungry so she went out for supplies, and came back with pizza and Doritos.
"The best part of that was when mom called me in labour and said, 'I'm about to take a swim and I was going to get a massage. How long do you think you're going to be labouring?'" Kate recalled. "I was like, 'I don't know mum'. I'm calling the nurse going, 'Do you know how long I would be labouring? Mom wants to swim."
The newborn will mark the 72-year-old's sixth grandchild. Her son Oliver already has three children.