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 3720 births resulting from inductions (out of 15857 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, 12437/15857 (78.4%) of spontaneous labors had already happened. But only 1271 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 8587 spontaneous labors before 41 weeks and 3550 spontaneous labors after 41 weeks. If all 1271 inductions were added to that "spontaneous" count, that'd mean there were 4821 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2162) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5712 babies would be born after 41 weeks. Remember, we'd need at least 8587 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 15857 100 3720 23.5
246 15826 99.8 3712 23.5
247 15801 99.6 3709 23.5
248 15775 99.5 3706 23.5
249 15740 99.3 3696 23.5
250 15703 99 3683 23.5
251 15665 98.8 3673 23.4
252 15636 98.6 3671 23.5
253 15570 98.2 3650 23.4
254 15525 97.9 3636 23.4
255 15466 97.5 3623 23.4
256 15411 97.2 3616 23.5
257 15360 96.9 3605 23.5
258 15297 96.5 3592 23.5
259 15216 96 3573 23.5
260 15083 95.1 3529 23.4
261 14964 94.4 3498 23.4
262 14847 93.6 3466 23.3
263 14722 92.8 3441 23.4
264 14578 91.9 3414 23.4
265 14433 91 3386 23.5
266 14249 89.9 3356 23.6
267 13996 88.3 3294 23.5
268 13781 86.9 3238 23.5
269 13557 85.5 3186 23.5
270 13292 83.8 3143 23.6
271 12944 81.6 3080 23.8
272 12628 79.6 3020 23.9
273 12253 77.3 2944 24
274 11715 73.9 2770 23.6
275 11245 70.9 2635 23.4
276 10646 67.1 2543 23.9
277 10077 63.5 2428 24.1
278 9511 60 2325 24.4
279 8958 56.5 2234 24.9
280 8359 52.7 2162 25.9
281 7131 45 1947 27.3
282 6429 40.5 1847 28.7
283 5791 36.5 1735 30
284 5191 32.7 1630 31.4
285 4615 29.1 1504 32.6
286 4026 25.4 1401 34.8
287 3420 21.6 1271 37.2
288 2747 17.3 1078 39.2
289 2207 13.9 906 41.1
290 1769 11.2 763 43.1
291 1328 8.4 605 45.6
292 1002 6.3 481 48
293 743 4.7 370 49.8
294 520 3.3 277 53.3
295 315 2 166 52.7
296 197 1.2 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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