My daughters midwife told her that after 42 weeks the placenta stops working. Is that correct?

Hi grandpa2014... congrats!

Technically, no, the placenta does not automatically stop working, but it may not work as effectively and there can be other concerns, such as a lessening in the amount of amniotic fluid, which can cause its own concerns.

Many pregnancies will go to 42 weeks, and some would naturally go a bit beyond, but you would be hard pressed to find many doctors or midwives who would be comfortable with going beyond 42 weeks because of the increase in possible problems.

Some care providers will take a wait-and-see approach, and use various tests, such as a stress test or a biophysical profile test to determine how baby is doing, level of amniotic fluid, etc. This may occur every couple of days or even daily. If things look good, they let the pregnancy continue. If baby, mother, or placenta start to show any concerns, they will intervene. However, it is not the norm for most care providers.

It most often happens that an induction will be suggested once a woman gets to 42 weeks, and often even sooner than that. The general thought is that it is safer to perform an induction than to let the pregnancy go post dates (later than 42 week).