How do you seriously not know?

A girl on my Facebook who I'm acquainted with from school years ago recently shared that she found out she's 7 months pregnant and didn't know. Freaking out asking people to buy her things from her registry...which she literally has all the big things on it like crib, mattress, changing table etc. She posted photos of her "baby bump" a few days later after she found out and she's fucking HUGE. Yes she was a bigger girl to begin with but her stomach and breasts are now sticking out so far there is no damn way she didn't know she was pregnant unless she's just a complete idiot. Now the exact same thing happened to another girl on my FB. 7 months pregnant before she said she knew she was pregnant but she's a tiny skinny girl and she was HUGE. Not to mention she just ignored the fact that she wasn't having periods and she had 3 kid already so how the FUCK did she not know!? I'm really baffled by both incidences. Have any of you been this far along and not known you were pregnant? Do you think these girls are idiots or in denial?