Hailey Bieber "magically" got pregnant with her son -- despite facing a potentially serious medical condition.

The Rhode founder, 29, has revealed she was diagnosed with a uterine septum before conceiving her now 16-month-old son Jack Blues, whom she shares with husband Justin Bieber, 32.

Speaking on the SHE MD podcast, Hailey recalled how Dr. ThaIs Aliabadi had urged caution before she fell pregnant.

She explained: "I had a septum in my uterus, and Dr. A kept saying, 'Well, we need to look at this and keep an eye on it before you get pregnant because it could potentially be an issue. I might have to give you a small surgery for it. Not sure.' And I was like, 'Okay. Well, I'm not thinking about getting pregnant right now, so we'll just cross that bridge when we get there.' And then I magically got pregnant."

Dr. Aliabadi admitted her reaction was one of alarm. The expert shared: "She calls me, and she's like, 'I'm pregnant!' And I'm like, 'No!'"

The doctor explained that a uterine septum -- which affects between one and three percent of women -- is a genetic condition in which a thin wall forms inside the uterine cavity. Hailey's was assessed as moderate, carrying a 25 to 40 percent risk of miscarriage and a 10 to 20 percent risk of preterm delivery.

Hailey reflected: "We realised as the baby was growing, the septum was expanding. Everything was opening and doing what it needed to do, luckily."

The model added that she had braced herself for an early labour.

She shared: "I was convinced I was going to go into labour early because of my mom's history. But my body had its own plan."

Meanwhile, Dr. Aliabadi administered the PreTRM Test -- an advanced blood test analysing placental proteins to estimate the risk of delivery -- which returned a low-risk result for Hailey.