Wilcox et al studied the probability that a woman would be in her 6 day fertile window on a specific day in her menstrual cycle. The timing of the fertile window can be highly unpredictable, with only a third of women having the fertile window entirely between days 10 and 17. The authors are from the National Institute of Environmental Health Sciences in Durham, North Carolina.
Parameters:
(1) cycle regular vs irregular
(2) if regular, the number of days in the cycle
|
|
Probability of Being in the Fertile Window |
||||
|---|---|---|---|---|---|
|
day of cycle |
irregular cycle |
regular cycle < 28 days |
regular cycle of 28 days |
regular cycle of 29 days |
regular cycle >= 30 days |
|
0 |
0.000 |
0.000 |
0.000 |
0.000 |
0.000 |
|
1.75 |
0.000 |
0.002 |
0.001 |
0.001 |
0.001 |
|
3.5 |
0.002 |
0.025 |
0.022 |
0.019 |
0.009 |
|
5.25 |
0.013 |
0.119 |
0.075 |
0.056 |
0.028 |
|
7 |
0.041 |
0.350 |
0.216 |
0.134 |
0.063 |
|
8.75 |
0.100 |
0.616 |
0.475 |
0.375 |
0.172 |
|
10.5 |
0.194 |
0.703 |
0.631 |
0.566 |
0.363 |
|
11.5 |
0.269 |
0.688 |
0.663 |
0.628 |
0.450 |
|
12.25 |
0.300 |
0.631 |
0.656 |
0.644 |
0.503 |
|
12.8 |
0.341 |
0.541 |
0.625 |
0.656 |
0.541 |
|
14 |
0.388 |
0.398 |
0.519 |
0.594 |
0.556 |
|
15.75 |
0.428 |
0.219 |
0.313 |
0.428 |
0.475 |
|
17.5 |
0.409 |
0.128 |
0.194 |
0.288 |
0.350 |
|
19.25 |
0.356 |
0.075 |
0.122 |
0.175 |
0.228 |
|
21 |
0.291 |
0.050 |
0.074 |
0.097 |
0.153 |
|
22.75 |
0.211 |
0.038 |
0.044 |
0.060 |
0.106 |
|
24.5 |
0.156 |
0.034 |
0.031 |
0.041 |
0.081 |
|
26.25 |
0.116 |
0.038 |
0.025 |
0.024 |
0.063 |
|
28 |
0.091 |
0.049 |
0.031 |
0.022 |
0.063 |
|
29.75 |
0.075 |
0.056 |
0.044 |
0.019 |
0.064 |
|
31.5 |
0.066 |
0.069 |
0.056 |
0.019 |
0.069 |
|
33.25 |
0.069 |
0.075 |
0.075 |
0.021 |
0.088 |
|
35 |
0.077 |
0.081 |
0.103 |
0.026 |
0.103 |
approximated from Figures 2 and 3, pages 1260-1261
Approximating Equations from JMP: Irregular Cycle
probability in fertile window for day 0 to 11.5 =
= (0.0002876 * ((day of cycle) ^3)) – (0.001458 * ((day of cycle) ^2)) + (0.002127 * (day of cycle)) – 0.000208
probability in fertile window for day 11.5 to 19.25 =
= (-0.000122 * ((day of cycle) ^3)) – (0.001685 * ((day of cycle) ^2)) + (0.1520585 * (day of cycle)) – 1.075533
probability in fertile window for day 19.25 to 29.75 =
= (0.0000726 * ((day of cycle) ^3)) – (0.003195 * ((day of cycle) ^2)) - (0.002957 * (day of cycle)) + 1.0822857
probability in fertile window for day 29.75 to 35 =
= (-0.000218 * ((day of cycle) ^3)) + (0.0225306 * ((day of cycle) ^2)) - (0.772476 * (day of cycle)) + 8.847
Approximating Equations from JMP: Regular Cycle of < 28 Days
probability in fertile window for day 0 to 8.75 =
= (0.000463 * ((day of cycle) ^3)) + (0.006471 * ((day of cycle) ^2)) - (0.021504 * (day of cycle)) + 0.0046984
probability in fertile window for day 8.75 to 12.25 =
= (-0.003236 * ((day of cycle) ^3)) + (0.0759629 * ((day of cycle) ^2)) - (0.510844 * (day of cycle)) + 1.4375909
probability in fertile window for day 12.25 to 21 =
= (-0.000491 * ((day of cycle) ^3)) + (0.0334244 * ((day of cycle) ^2)) - (0.761041 * (day of cycle)) + 5.8401134
probability in fertile window for day 21 to 28 =
= (-0.000016 * ((day of cycle) ^3)) + (0.0024023 * ((day of cycle) ^2)) - (0.089667 * (day of cycle)) + 1.0175857
probability in fertile window for day 28 to 35 =
= (-0.000093 * ((day of cycle) ^3)) + (0.0086064 * ((day of cycle) ^2)) - (0.258776 * (day of cycle)) + 2.595
Approximating Equations from JMP: Regular Cycle of 28 Days
probability in fertile window for day 0 to 8.75 =
= (0.0011368 * ((day of cycle) ^3)) – (0.0046 * ((day of cycle) ^2)) + (0.0075616 * (day of cycle)) – 0.000921
probability in fertile window for day 8.75 to 14 =
= (-0.000583 * ((day of cycle) ^3)) – (0.003965 * ((day of cycle) ^2)) + (0.3287014 * (day of cycle)) – 1.707444
probability in fertile window for day 14 to 26.25 =
= (-0.000402 * ((day of cycle) ^3)) + (0.0290718 * ((day of cycle) ^2)) - (0.706321 * (day of cycle)) + 5.808474
probability in fertile window for day 26.25 to 35 =
= (0.0000587 * ((day of cycle) ^3)) – (0.004615 * ((day of cycle) ^2)) + (0.1252305 * (day of cycle)) – 1.144889
Approximating Equations from JMP: Regular Cycle of 29 Days
probability in fertile window for day 0 to 10.5 =
= (0.0003991 * ((day of cycle) ^3)) + (0.0020603 * ((day of cycle) ^2)) - (0.010923 * (day of cycle)) + 0.005
probability in fertile window for day 10.5 to 15.75 =
= (0.0009901 * ((day of cycle) ^4)) – (0.051103 * ((day of cycle) ^3)) + (0.9607751 * ((day of cycle) ^2)) - (7.796999 * (day of cycle)) + 23.633397
probability in fertile window for day 15.75 to 29.75 =
= (-0.000219 * ((day of cycle) ^3)) + (0.0183492 * ((day of cycle) ^2)) - (0.512868 * (day of cycle)) + 4.8137222
probability in fertile window for day 29.75 to 35=
= (0.0000311 * ((day of cycle) ^3)) – (0.002612 * ((day of cycle) ^2)) + (0.0724762 * (day of cycle)) – 0.644
Approximating Equations from JMP: Regular Cycle of >= 30 Days
probability in fertile window for day 0 to 11.5 =
= (0.0004607 * ((day of cycle) ^3)) – (0.001963 * ((day of cycle) ^2)) + (0.0019073 * (day of cycle)) + 0.0014143
probability in fertile window for day 11.5 to 15.75 =
= (-0.000406 * ((day of cycle) ^3)) – (0.004533 * ((day of cycle) ^2)) + (0.357417 * (day of cycle)) – 2.444863
probability in fertile window for day 15.75 to 29.75 =
= (-0.00015 * ((day of cycle) ^3)) + (0.0135822 * ((day of cycle) ^2)) - (0.408112 * (day of cycle)) + 4.1223968
probability in fertile window for day 29.75 to 35 =
= (0.0008163 * ((day of cycle) ^2)) - (0.045086 * (day of cycle)) + 0.6819
Specialty: Obstetrics & Gynecology
ICD-10: ,
