Or the baby will be teeny tiny.  Fat women who don't develop gestational diabetes often give birth to tiny babies due to blood inflammation caused by obesity. Her baby will either be a 15-pounder or it will barely break five pounds and will have reduced lung capacity.  There will be no inbetween. My money is on pre-eclampsia forcing a 35-week c-section and the baby being in NICU for a month, minimum.