The clock is ticking, Science Mum is approaching 35 weeks pregnant and (of course) glowing! Meanwhile, it's ski season, and the lads are packing for a week of alpine fun and apres-ski. It will probably be my last chance to ski for a long long time, should I join them?
First, let's ask the panel of "old-wives". The result: a resounding: "The first child is usually late". According to this article, first children are indeed less likely to be on time, but are in fact more likely to be early. Sorry, old wives, you got it wrong.
It's not a new question. A cursory google-image search reveals the weekly probabilities from Minnesota:
The UK Office for National Statistics (ONS) suggests that about 5-7% of babies are born between 32-36 weeks (depending on ethnicity).
So, what's the probability of Science Baby arriving in the 35th week? Reading directly from the Minnesota graph, it's 2%. From the daily graph, adding the probabilities from 42 to 35 days early gives a number less than 1.5%. I also calculate 1.5% when dividing the ONS data into 4 equal weeks.
OK, a 1.5% chance is pretty slim. Probably worth the gamble, right?
Yes, but you'd have to adjust the probabilities given that your baby wasn't born before now, ie in weeks with a non zero probability in the average distribution
ReplyDeleteVery good point! In my case the adjustment would have been negligible, but in some cases the effect could be huge. For example, what if the pregnancy has reached week 45? From the graph, the prior probability is low at 1%, but the chance of the baby being born this week is close to 100%.
DeleteVery good point! In my case the adjustment would have been negligible, but in some cases the effect could be huge. For example, what if the pregnancy has reached week 45? From the graph, the prior probability is low at 1%, but the chance of the baby being born this week is close to 100%.
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