They told me the same. Lung development is better at 39 and because baby isn’t squeezed coming through birth canal they’re more likely to experience breathing problems already.
In my case, if baby gets so big they’re likely to come before they might do it earlier because then the safety risk to me becomes worse than the risk baby would have a problem - so pretty much, all done on a balance of risk but all being equal, the optimum for baby is to come 39+
it’s worth noting that if you go into labour spontaneously and have contractions, that also helps stimulate the babies lungs and prepare/mature them for birth (regardless of how they are born)
although, with that being said… I laboured for almost 70 hours with my first, delivered at 39w exactly by EMCS and they still sounded gurgly for the first day or two after being born (although didn’t need any help with breathing other than a really hard rub down to get them crying!)
On the flip side I know someone who went into spontaneous labour at 36+5, delivered by EMCS and had a 5lber compared to my 7lber and had zero breathing issues or gurglyness at all!
we’ve been offered steroids for the twins (even if I reach my elective date of 37+3) and I’m not yet sure it’s something we will say yes to upon reading into it and the evidence associated with having them after 37w.
like you say it’s all about balancing risk of mum/baby, but I find it reassuring to remind myself that babies lungs are fully developed by the end of the 36th week.