She added: "I am having a baby... It's growing! If two are in there I might just lose it."
Spears also revealed how she plans to avoid the paparazzi who she says will want to profit off pictures of her pregnant.
"I obviously won't be going out as much due to the paps getting their money shot of me like they unfortunately already have.
"It's hard because when I was pregnant I had perinatal depression. I have to say it is absolutely horrible. Women didn't talk about it back then, but now women talk about it every day!"
Britney concluded: "This time I will be doing yoga every day! Spreading lots of joy and love."
The hitmaker already shares two sons, 15-year-old Jaden and 16-year-old Sean, with her ex-husband Kevin Federline.
A source previously told the Sun that the singer is hoping to have a baby girl.
"Britney definitely wants more kids and she would be so happy and grateful with another son but deep down, her desire is to be a mama to a little girl," the source said.
They continued: "She wants to pass down her dresses and take her daughter to dance class, things her sons are not interested in."
Spears first spoke of wanting another child in June last year during a hearing for her conservatorship. She revealed in a court testimony that becoming a mother for a third time was not possible for the Grammy winner while her father still had conservator rights.
"I would like to progressively move forward and I want to have the real deal. I want to be able to get married and have a baby."
Spears went on to tell the court, "I have an [IUD] inside of myself so I don't get pregnant. They don't want me to have children — any more children."
The singer has always spoken highly of being a mother and told People in 2017, "I am so lucky that I get to experience all of life's adventures with them", and stated there is "nothing more rewarding" than being a mother.
