Probablity of Induction after a given day

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Induction odds by day

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 3812 births resulting from inductions (out of 16167 total). Only 7% (280) 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, 12641/16167 (78.2%) of spontaneous labors had already happened. But only 1299 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 8696 spontaneous labors before 41 weeks and 3659 spontaneous labors after 41 weeks. If all 1299 inductions were added to that "spontaneous" count, that'd mean there were 4958 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2191) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5850 babies would be born after 41 weeks. Remember, we'd need at least 8696 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.

Does the data change for first time mothers?

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

Induction odds by day

DayTotal pregnancies remainingHow many will end in induction
#% #%
245 16167 100 3812 23.6
246 16133 99.8 3803 23.6
247 16105 99.6 3799 23.6
248 16077 99.4 3796 23.6
249 16042 99.2 3786 23.6
250 16005 99 3773 23.6
251 15967 98.8 3763 23.6
252 15938 98.6 3761 23.6
253 15870 98.2 3740 23.6
254 15825 97.9 3726 23.5
255 15762 97.5 3712 23.6
256 15703 97.1 3703 23.6
257 15650 96.8 3691 23.6
258 15584 96.4 3677 23.6
259 15502 95.9 3658 23.6
260 15365 95 3612 23.5
261 15238 94.3 3577 23.5
262 15115 93.5 3540 23.4
263 14990 92.7 3515 23.4
264 14839 91.8 3488 23.5
265 14686 90.8 3457 23.5
266 14496 89.7 3427 23.6
267 14226 88 3357 23.6
268 13996 86.6 3297 23.6
269 13763 85.1 3242 23.6
270 13489 83.4 3197 23.7
271 13133 81.2 3133 23.9
272 12806 79.2 3071 24
273 12418 76.8 2995 24.1
274 11862 73.4 2814 23.7
275 11376 70.4 2674 23.5
276 10928 67.6 2580 23.6
277 10345 64 2463 23.8
278 9765 60.4 2358 24.1
279 9195 56.9 2265 24.6
280 8579 53.1 2191 25.5
281 7336 45.4 1997 27.2
282 6611 40.9 1890 28.6
283 5955 36.8 1776 29.8
284 5335 33 1668 31.3
285 4744 29.3 1539 32.4
286 4146 25.6 1432 34.5
287 3526 21.8 1299 36.8
288 2835 17.5 1102 38.9
289 2279 14.1 924 40.5
290 1826 11.3 777 42.6
291 1371 8.5 617 45
292 1033 6.4 489 47.3
293 761 4.7 373 49
294 532 3.3 280 52.6
295 322 2 167 51.9
296 202 1.2 91 45
297 132 0.8 53 40.2
298 83 0.5 32 38.6
299 61 0.4 23 37.7
300 35 0.2 12 34.3

Due Date Survey Data

Due 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
Birth Stories
Survey input dates

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