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 3669 births resulting from inductions (out of 15472 total). Only 7% (275) 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, 12107/15472 (78.3%) of spontaneous labors had already happened. But only 1251 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 8308 spontaneous labors before 41 weeks and 3495 spontaneous labors after 41 weeks. If all 1251 inductions were added to that "spontaneous" count, that'd mean there were 4746 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2133) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5628 babies would be born after 41 weeks. Remember, we'd need at least 8308 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 15472 100 3669 23.7
246 15441 99.8 3661 23.7
247 15416 99.6 3658 23.7
248 15391 99.5 3655 23.7
249 15356 99.3 3645 23.7
250 15319 99 3632 23.7
251 15282 98.8 3622 23.7
252 15255 98.6 3620 23.7
253 15189 98.2 3599 23.7
254 15145 97.9 3585 23.7
255 15086 97.5 3572 23.7
256 15031 97.1 3565 23.7
257 14982 96.8 3554 23.7
258 14920 96.4 3541 23.7
259 14840 95.9 3522 23.7
260 14708 95.1 3479 23.7
261 14593 94.3 3449 23.6
262 14479 93.6 3418 23.6
263 14355 92.8 3393 23.6
264 14214 91.9 3367 23.7
265 14071 90.9 3339 23.7
266 13890 89.8 3309 23.8
267 13649 88.2 3248 23.8
268 13435 86.8 3192 23.8
269 13211 85.4 3140 23.8
270 12948 83.7 3098 23.9
271 12607 81.5 3039 24.1
272 12296 79.5 2981 24.2
273 11923 77.1 2905 24.4
274 11390 73.6 2735 24
275 10927 70.6 2601 23.8
276 10492 67.8 2510 23.9
277 9934 64.2 2397 24.1
278 9375 60.6 2295 24.5
279 8827 57.1 2204 25
280 8235 53.2 2133 25.9
281 7026 45.4 1919 27.3
282 6335 40.9 1822 28.8
283 5706 36.9 1712 30
284 5118 33.1 1608 31.4
285 4551 29.4 1483 32.6
286 3969 25.7 1381 34.8
287 3365 21.7 1251 37.2
288 2707 17.5 1062 39.2
289 2175 14.1 892 41
290 1749 11.3 754 43.1
291 1314 8.5 599 45.6
292 992 6.4 476 48
293 736 4.8 366 49.7
294 515 3.3 275 53.4
295 311 2 164 52.7
296 197 1.3 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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