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 3774 births resulting from inductions (out of 16028 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, 12525/16028 (78.1%) of spontaneous labors had already happened. But only 1293 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 8619 spontaneous labors before 41 weeks and 3635 spontaneous labors after 41 weeks. If all 1293 inductions were added to that "spontaneous" count, that'd mean there were 4928 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2176) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5811 babies would be born after 41 weeks. Remember, we'd need at least 8619 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 16028 100 3774 23.5
246 15994 99.8 3765 23.5
247 15967 99.6 3761 23.6
248 15939 99.4 3758 23.6
249 15904 99.2 3748 23.6
250 15867 99 3735 23.5
251 15829 98.8 3725 23.5
252 15800 98.6 3723 23.6
253 15733 98.2 3702 23.5
254 15688 97.9 3688 23.5
255 15625 97.5 3674 23.5
256 15568 97.1 3667 23.6
257 15515 96.8 3655 23.6
258 15450 96.4 3642 23.6
259 15368 95.9 3623 23.6
260 15233 95 3578 23.5
261 15110 94.3 3545 23.5
262 14989 93.5 3510 23.4
263 14864 92.7 3485 23.4
264 14714 91.8 3458 23.5
265 14562 90.9 3427 23.5
266 14373 89.7 3397 23.6
267 14108 88 3328 23.6
268 13885 86.6 3270 23.6
269 13655 85.2 3217 23.6
270 13383 83.5 3172 23.7
271 13030 81.3 3108 23.9
272 12705 79.3 3046 24
273 12322 76.9 2970 24.1
274 11773 73.5 2793 23.7
275 11295 70.5 2656 23.5
276 10852 67.7 2563 23.6
277 10271 64.1 2446 23.8
278 9698 60.5 2343 24.2
279 9133 57 2250 24.6
280 8520 53.2 2176 25.5
281 7288 45.5 1984 27.2
282 6569 41 1879 28.6
283 5920 36.9 1767 29.8
284 5304 33.1 1659 31.3
285 4715 29.4 1530 32.4
286 4120 25.7 1425 34.6
287 3503 21.9 1293 36.9
288 2815 17.6 1096 38.9
289 2264 14.1 919 40.6
290 1815 11.3 774 42.6
291 1361 8.5 614 45.1
292 1027 6.4 488 47.5
293 757 4.7 373 49.3
294 529 3.3 280 52.9
295 320 2 167 52.2
296 201 1.3 91 45.3
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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