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 3779 births resulting from inductions (out of 16069 total). Only 7% (280) 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, 12560/16069 (78.2%) of spontaneous labors had already happened. But only 1295 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 8649 spontaneous labors before 41 weeks and 3641 spontaneous labors after 41 weeks. If all 1295 inductions were added to that "spontaneous" count, that'd mean there were 4936 babies born after 41 weeks... not enough to tip the scales. What if all the inductions after 40 weeks (2180) were actually supposed to be spontaneous labors after 41 weeks? That'd mean 5821 babies would be born after 41 weeks. Remember, we'd need at least 8649 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 16069 100 3779 23.5
246 16035 99.8 3770 23.5
247 16008 99.6 3766 23.5
248 15980 99.4 3763 23.5
249 15945 99.2 3753 23.5
250 15908 99 3740 23.5
251 15870 98.8 3730 23.5
252 15841 98.6 3728 23.5
253 15774 98.2 3707 23.5
254 15729 97.9 3693 23.5
255 15666 97.5 3679 23.5
256 15609 97.1 3672 23.5
257 15556 96.8 3660 23.5
258 15491 96.4 3647 23.5
259 15409 95.9 3628 23.5
260 15274 95.1 3583 23.5
261 15151 94.3 3550 23.4
262 15030 93.5 3515 23.4
263 14905 92.8 3490 23.4
264 14755 91.8 3463 23.5
265 14603 90.9 3432 23.5
266 14414 89.7 3402 23.6
267 14149 88.1 3333 23.6
268 13922 86.6 3275 23.5
269 13692 85.2 3222 23.5
270 13420 83.5 3177 23.7
271 13066 81.3 3113 23.8
272 12741 79.3 3051 23.9
273 12355 76.9 2975 24.1
274 11805 73.5 2797 23.7
275 11325 70.5 2660 23.5
276 10881 67.7 2567 23.6
277 10298 64.1 2450 23.8
278 9725 60.5 2347 24.1
279 9159 57 2254 24.6
280 8545 53.2 2180 25.5
281 7308 45.5 1988 27.2
282 6587 41 1883 28.6
283 5932 36.9 1770 29.8
284 5314 33.1 1662 31.3
285 4723 29.4 1533 32.5
286 4127 25.7 1427 34.6
287 3509 21.8 1295 36.9
288 2821 17.6 1098 38.9
289 2269 14.1 921 40.6
290 1819 11.3 775 42.6
291 1365 8.5 615 45.1
292 1031 6.4 489 47.4
293 759 4.7 373 49.1
294 530 3.3 280 52.8
295 321 2 167 52
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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