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 3740 births resulting from inductions (out of 15894 total). Only 7% (278) 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, 12424/15894 (78.2%) of spontaneous labors had already happened. But only 1284 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 8553 spontaneous labors before 41 weeks and 3601 spontaneous labors after 41 weeks. If all 1284 inductions were added to that "spontaneous" count, that'd mean there were 4885 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2159) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5760 babies would be born after 41 weeks. Remember, we'd need at least 8553 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 15894 100 3740 23.5
246 15862 99.8 3732 23.5
247 15836 99.6 3729 23.5
248 15808 99.5 3726 23.6
249 15773 99.2 3716 23.6
250 15736 99 3703 23.5
251 15698 98.8 3693 23.5
252 15669 98.6 3691 23.6
253 15602 98.2 3670 23.5
254 15557 97.9 3656 23.5
255 15495 97.5 3642 23.5
256 15439 97.1 3635 23.5
257 15387 96.8 3623 23.5
258 15322 96.4 3610 23.6
259 15241 95.9 3591 23.6
260 15108 95.1 3547 23.5
261 14986 94.3 3515 23.5
262 14866 93.5 3480 23.4
263 14741 92.7 3455 23.4
264 14591 91.8 3428 23.5
265 14444 90.9 3399 23.5
266 14255 89.7 3369 23.6
267 13993 88 3301 23.6
268 13775 86.7 3243 23.5
269 13548 85.2 3191 23.6
270 13280 83.6 3147 23.7
271 12930 81.4 3083 23.8
272 12609 79.3 3022 24
273 12226 76.9 2946 24.1
274 11683 73.5 2770 23.7
275 11208 70.5 2634 23.5
276 10768 67.7 2542 23.6
277 10192 64.1 2427 23.8
278 9623 60.5 2324 24.2
279 9063 57 2232 24.6
280 8455 53.2 2159 25.5
281 7233 45.5 1970 27.2
282 6520 41 1867 28.6
283 5874 37 1755 29.9
284 5262 33.1 1648 31.3
285 4678 29.4 1519 32.5
286 4084 25.7 1415 34.6
287 3470 21.8 1284 37
288 2788 17.5 1089 39.1
289 2240 14.1 913 40.8
290 1798 11.3 769 42.8
291 1349 8.5 609 45.1
292 1017 6.4 485 47.7
293 751 4.7 371 49.4
294 526 3.3 278 52.9
295 318 2 166 52.2
296 200 1.3 90 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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