I dont think its got anything to do with the stomach muscles, thats just the way Imogen interprets it cause shes thick. I think the real reason will be as said the baby is breech
I would imagine the stomach muscle mention is about attempting external cephalic version. This is where the obstetrician attempts to turn the baby from the outside through the abdomen. (As the midwife did in CTM this week) The problem with this is its very difficult to do if the mother has strong tummy muscles.
On a mother nature note, breech babies are usually breech for a reason, Usually a case of CPD where the baby will not fit through the pelvis head first so mother nature decides to not turn baby. Obviously not realising the implications.
When I was practising as a midwife in the mid 90's it wasn't routine to section all breech babies, most parents were given a choice, as generally a vaginal birth is safer for mother.
However with the shortage of midwives/obstetricians it would be deemed too risky in this litigation strewn world.
The sad thing is, if not used the skill to deliver a breech baby vaginally will be lost