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 3735 births resulting from inductions (out of 16049 total). Only 7% (277) 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, 12608/16049 (78.6%) of spontaneous labors had already happened. But only 1275 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 8743 spontaneous labors before 41 weeks and 3571 spontaneous labors after 41 weeks. If all 1275 inductions were added to that "spontaneous" count, that'd mean there were 4846 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2168) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5739 babies would be born after 41 weeks. Remember, we'd need at least 8743 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 16049 100 3735 23.3
246 16018 99.8 3727 23.3
247 15993 99.7 3724 23.3
248 15967 99.5 3721 23.3
249 15932 99.3 3711 23.3
250 15895 99 3698 23.3
251 15857 98.8 3688 23.3
252 15828 98.6 3686 23.3
253 15762 98.2 3665 23.3
254 15717 97.9 3651 23.2
255 15657 97.6 3637 23.2
256 15602 97.2 3630 23.3
257 15550 96.9 3618 23.3
258 15485 96.5 3605 23.3
259 15404 96 3586 23.3
260 15271 95.2 3542 23.2
261 15152 94.4 3511 23.2
262 15033 93.7 3477 23.1
263 14908 92.9 3452 23.2
264 14762 92 3425 23.2
265 14616 91.1 3396 23.2
266 14431 89.9 3366 23.3
267 14178 88.3 3304 23.3
268 13963 87 3248 23.3
269 13739 85.6 3196 23.3
270 13472 83.9 3153 23.4
271 13124 81.8 3090 23.5
272 12806 79.8 3029 23.7
273 12427 77.4 2953 23.8
274 11886 74.1 2777 23.4
275 11413 71.1 2641 23.1
276 10710 66.7 2549 23.8
277 10137 63.2 2434 24
278 9570 59.6 2331 24.4
279 9014 56.2 2240 24.9
280 8411 52.4 2168 25.8
281 7174 44.7 1952 27.2
282 6467 40.3 1852 28.6
283 5824 36.3 1740 29.9
284 5219 32.5 1634 31.3
285 4640 28.9 1508 32.5
286 4051 25.2 1405 34.7
287 3441 21.4 1275 37.1
288 2765 17.2 1082 39.1
289 2223 13.9 908 40.8
290 1784 11.1 765 42.9
291 1337 8.3 606 45.3
292 1007 6.3 482 47.9
293 746 4.6 370 49.6
294 522 3.3 277 53.1
295 316 2 166 52.5
296 198 1.2 90 45.5
297 130 0.8 53 40.8
298 81 0.5 32 39.5
299 59 0.4 23 39
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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