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 3695 births resulting from inductions (out of 15670 total). Only 7% (276) 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, 12272/15670 (78.3%) of spontaneous labors had already happened. But only 1261 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 8447 spontaneous labors before 41 weeks and 3528 spontaneous labors after 41 weeks. If all 1261 inductions were added to that "spontaneous" count, that'd mean there were 4789 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2148) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5676 babies would be born after 41 weeks. Remember, we'd need at least 8447 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 15670 100 3695 23.6
246 15639 99.8 3687 23.6
247 15614 99.6 3684 23.6
248 15588 99.5 3681 23.6
249 15553 99.3 3671 23.6
250 15516 99 3658 23.6
251 15478 98.8 3648 23.6
252 15449 98.6 3646 23.6
253 15383 98.2 3625 23.6
254 15339 97.9 3611 23.5
255 15280 97.5 3598 23.5
256 15225 97.2 3591 23.6
257 15176 96.8 3580 23.6
258 15114 96.5 3567 23.6
259 15033 95.9 3548 23.6
260 14900 95.1 3504 23.5
261 14784 94.3 3474 23.5
262 14668 93.6 3442 23.5
263 14544 92.8 3417 23.5
264 14402 91.9 3391 23.5
265 14257 91 3363 23.6
266 14075 89.8 3333 23.7
267 13825 88.2 3271 23.7
268 13610 86.9 3215 23.6
269 13386 85.4 3163 23.6
270 13121 83.7 3120 23.8
271 12776 81.5 3059 23.9
272 12461 79.5 3000 24.1
273 12087 77.1 2924 24.2
274 11551 73.7 2752 23.8
275 11082 70.7 2617 23.6
276 10585 67.5 2526 23.9
277 10022 64 2413 24.1
278 9460 60.4 2311 24.4
279 8908 56.8 2220 24.9
280 8312 53 2148 25.8
281 7091 45.3 1933 27.3
282 6393 40.8 1835 28.7
283 5759 36.8 1725 30
284 5166 33 1620 31.4
285 4592 29.3 1494 32.5
286 4004 25.6 1391 34.7
287 3398 21.7 1261 37.1
288 2730 17.4 1069 39.2
289 2193 14 898 40.9
290 1761 11.2 757 43
291 1324 8.4 601 45.4
292 999 6.4 478 47.8
293 741 4.7 368 49.7
294 519 3.3 276 53.2
295 314 2 165 52.5
296 197 1.3 90 45.7
297 129 0.8 53 41.1
298 80 0.5 32 40
299 58 0.4 23 39.7
300 34 0.2 12 35.3

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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