Here's the big question this graph is trying to answer:
The western world likes to induce babies rather than let them go too late, doesn't this skew your results by removing late babies from the "late" end of the spectrum where they should be?
I don't think so. This survey contained 3669 births resulting from inductions (out of 15472 total). Only 7% (275) of the inductions were at or past 42 weeks, 0 D. By that time, 96.7% of all spontenous labors have already happened. At 41 weeks 0 days, 12107/15472 (78.3%) of spontaneous labors had already happened. But only 1251 inductions happened after that date.
There's a study that suggests the average first time mom goes into labor 8 days past her due date. Even though the study is 20 years old, the notion of moving everyone's due date to 41W1D has not caught on. Why not?
The survey results show that there were 8308 spontaneous labors before 41 weeks and 3495 spontaneous labors after 41 weeks. If all 1251 inductions were added to that "spontaneous" count, that'd mean there were 4746 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2133) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5628 babies would be born after 41 weeks. Remember, we'd need at least 8308 to happen spontaneously after 41 weeks to match the ones that spontaneously happened before 41 weeks; a median means that half happen before, half after. It'd be tough for the median to move a whole 7 or 8 days. It all tells me that reducing inductions will not shift the median to the right a whole lot.
I've also added a table here that shows how the median would shift if ALL inductions, not just the later ones, were actually supposed to be "late" births.
I've received a lot of questions about whether these statistics shift for first time mothers. You can click here to exclude all non first-time moms
|Day||Total pregnancies remaining||How many will end in induction|
Due Date Survey DataDue date statistics: A study on the length of pregnancy
Probability of delivery resulting from spontaneous labor after 35 weeks
Probability of delivery within x days of a given date
Length of pregnancy by week
Spontaneous labor and due date determination
Length of pregnancy, comparing subsequent births for individual moms
Length of pregnancy for first time vs. second & third time moms
Length of pregnancy, type of delivery
Gestation vs. Birthweight
Probablity of Induction after a given day
Average day of spontaneous labor vs. age of mother at time of birth
Are more babies born during a full moon?
What's the most common day of the week for babies to be born?
I'm still pregnant at 40W. What's it mean?
Do winter babies arrive later?
What if I know my conception date?
Are boys or girls born later?
Subsequent pregnancy date search
How do inductions bias the due date statistics?
Download the data
Survey input dates
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