as ever , the nice guidelines come into play.
previous versions had a line stating 'the risks of induction do not exceed those of going post-term until +14' which has now been removed. as there hasn't been any new research (due to the policy being so widely applied) i don't know why that line was removed. maybe so we don't quote it at HCPs :)
from the evidence tables, the risks are -
Probability of intrapartum stillbirth (per 1000 live birth):
At 37 weeks: 0.7
At 38 weeks: 0.3
At 39 weeks: 0.2
At 40 weeks: 0.3
At 41 weeks: 0.3
At 42 weeks: 0.4
At 43 weeks: 0
so the risk from induction would probably be 0.4 per 1000 at 42 weeks, or only slightly less. seems like a very crudely applied statistic though to be fair, the research is really old, and i haven't managed to find current details of how it was done.
these Norwegian stats -
Fetal complications
Meconium aspiration (per 1000 births)
At 37 weeks: 2.5
At 38 weeks: 2.3
At 39 weeks: 1.8
At 40 weeks: 2.9
At 41 weeks: 5.1
At 42 weeks: 4.7
Intrauterine fetal death (per 1000 ongoing pregnancies)
At 37 weeks: 0.35
At 38 weeks: 0.25
At 39 weeks: 0.43
At 40 weeks: 0.51
At 41 weeks: 0.84
At 42 weeks: 1.55
different again...
i think since then average gestations have increased (taller, fatter mothers cooking larger babies...) and it is hard to know if the +42 stat is still accurate, if it ever was....
problem is, only 3% of women go past 42 weeks....and what i didn't find was a re-study showing that inducing those women reduced their chance of stillbirth. (ie, was the fact of going post-term at that point an indication of a problem that induction wasn't going to help?)
I'd be interested in a study that followed women to 42 weeks, and compared those spontaneously labouring at +14 with those induced ...there does seem an element of iatrogenic disturbance to these 'late' labours, e.g my sisters friend who turned up in established labour to be told they still wanted to induce her! the argument was so stressful her labour stopped and she went home. In the end she went back in when contractions returned....forceps delivery...possibly avoidable without the initial crap.
if spontaneous labour was found to be safer, then maybe +15 could be tried...etc etc...it seems otherwise they are stuck doing this for want of more recent evidence, without being sure it improves outcomes.