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 3757 births resulting from inductions (out of 15966 total). Only 7% (279) 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, 12478/15966 (78.2%) of spontaneous labors had already happened. But only 1287 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 8590 spontaneous labors before 41 weeks and 3619 spontaneous labors after 41 weeks. If all 1287 inductions were added to that "spontaneous" count, that'd mean there were 4906 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2165) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5784 babies would be born after 41 weeks. Remember, we'd need at least 8590 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 15966 100 3757 23.5
246 15932 99.8 3748 23.5
247 15905 99.6 3744 23.5
248 15877 99.4 3741 23.6
249 15842 99.2 3731 23.6
250 15805 99 3718 23.5
251 15767 98.8 3708 23.5
252 15738 98.6 3706 23.5
253 15671 98.2 3685 23.5
254 15626 97.9 3671 23.5
255 15564 97.5 3657 23.5
256 15507 97.1 3650 23.5
257 15454 96.8 3638 23.5
258 15389 96.4 3625 23.6
259 15308 95.9 3606 23.6
260 15174 95 3562 23.5
261 15051 94.3 3529 23.4
262 14930 93.5 3494 23.4
263 14805 92.7 3469 23.4
264 14655 91.8 3442 23.5
265 14505 90.8 3413 23.5
266 14316 89.7 3383 23.6
267 14051 88 3314 23.6
268 13832 86.6 3256 23.5
269 13603 85.2 3203 23.5
270 13334 83.5 3159 23.7
271 12982 81.3 3095 23.8
272 12659 79.3 3033 24
273 12276 76.9 2957 24.1
274 11728 73.5 2780 23.7
275 11251 70.5 2643 23.5
276 10809 67.7 2550 23.6
277 10230 64.1 2434 23.8
278 9659 60.5 2331 24.1
279 9097 57 2239 24.6
280 8487 53.2 2165 25.5
281 7261 45.5 1975 27.2
282 6544 41 1871 28.6
283 5896 36.9 1759 29.8
284 5283 33.1 1651 31.3
285 4697 29.4 1522 32.4
286 4103 25.7 1418 34.6
287 3488 21.8 1287 36.9
288 2804 17.6 1091 38.9
289 2255 14.1 915 40.6
290 1809 11.3 771 42.6
291 1356 8.5 611 45.1
292 1024 6.4 487 47.6
293 755 4.7 372 49.3
294 528 3.3 279 52.8
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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