The woman in the article that miscarried? That could be a health problem. I didn’t form enough/barely measurable amniotic fluid with my first pregnancy. Not going to indict this woman without more medical history.
In the other instance posted about a friend, the very obese woman probably didn’t have regular menstrual cycles; so missing 8 months or so would not be out of the ordinary and not clue one into the possibility of a pregnancy.
But, I would say that I started actually feeling both of my children around 4-5 months. So even if there is no menstrual evidence, there is other things happening.