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 3746 births resulting from inductions (out of 16247 total). Only 7% (278) of the inductions were at or past 42 weeks, 0 D. By that time, 96.8% of all spontenous labors have already happened. At 41 weeks 0 days, 12796/16247 (78.8%) of spontaneous labors had already happened. But only 1279 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 8920 spontaneous labors before 41 weeks and 3581 spontaneous labors after 41 weeks. If all 1279 inductions were added to that "spontaneous" count, that'd mean there were 4860 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2177) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5758 babies would be born after 41 weeks. Remember, we'd need at least 8920 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 16247 100 3746 23.1
246 16216 99.8 3738 23.1
247 16191 99.7 3735 23.1
248 16163 99.5 3732 23.1
249 16128 99.3 3722 23.1
250 16091 99 3709 23.1
251 16053 98.8 3699 23
252 16024 98.6 3697 23.1
253 15958 98.2 3676 23
254 15913 97.9 3662 23
255 15853 97.6 3648 23
256 15798 97.2 3641 23
257 15746 96.9 3629 23
258 15681 96.5 3616 23.1
259 15600 96 3597 23.1
260 15467 95.2 3553 23
261 15348 94.5 3522 22.9
262 15229 93.7 3488 22.9
263 15104 93 3463 22.9
264 14958 92.1 3436 23
265 14812 91.2 3407 23
266 14626 90 3377 23.1
267 14373 88.5 3315 23.1
268 14157 87.1 3259 23
269 13932 85.8 3207 23
270 13665 84.1 3164 23.2
271 13317 82 3101 23.3
272 12998 80 3040 23.4
273 12618 77.7 2964 23.5
274 12077 74.3 2788 23.1
275 11603 71.4 2652 22.9
276 10743 66.1 2560 23.8
277 10170 62.6 2445 24
278 9602 59.1 2342 24.4
279 9044 55.7 2250 24.9
280 8439 51.9 2177 25.8
281 7194 44.3 1961 27.3
282 6486 39.9 1860 28.7
283 5842 36 1748 29.9
284 5235 32.2 1641 31.3
285 4654 28.6 1513 32.5
286 4063 25 1409 34.7
287 3451 21.2 1279 37.1
288 2775 17.1 1086 39.1
289 2230 13.7 911 40.9
290 1789 11 767 42.9
291 1341 8.3 607 45.3
292 1011 6.2 483 47.8
293 749 4.6 371 49.5
294 525 3.2 278 53
295 318 2 166 52.2
296 200 1.2 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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