She didn't. Neither did the Army docs. She'd had at least two physicals during this time. She was seen because she didn't understand why her period stopped for four+/- months. She lost about 35 pounds and they chalked it up to that. She legit did not know. Her Dad, managed to make it with 20 minutes to spare for the delivery, he saw the genuine shock she was in, and the fierce Mama Bear take over when the hydrocephalus was diagnosed.
I found this that explains how it can happen in the military "—gave birth without knowing they were pregnant until labor began. These rare "
cryptic pregnancies" often involve high-stress environments, intense physical training, and the absence of typical symptoms, leading to unexpected births in military medical facilities." and if you add to that a baby that doesn't move because moving = pain, and you get a Baby Sophia.