Smith et al used probability models for estimating the risk of cesarean section for a pregnant woman. The authors are from Cambridge University, Austin Community College (Texas), and NHS Board Glasgow.
Patient selection: pregnant woman with singleton fetus
Parameters (Table III, page 2032).
(1) maternal age
(2) maternal height in centimeters
(3) week gestation
(4) gender of fetus
|
Maternal Age |
Likelihood Ratio |
|
< 16 years |
NA |
|
16 to 26 years |
(0.003298 * ((age)^2)) - (0.07917 * (age)) + 0.8150 |
|
26 to 48 years |
(0.000081 * ((age)^2)) + (0.09836 * (age)) - 1.653 |
|
> 48 years |
NA |
|
Maternal Height |
Likelihood Ratio |
|
< 143 cm |
NA |
|
143 to 152 |
(0.02981 * ((hgt)^2)) - (9.225 * (hgt)) + 715.8 |
|
152 to 164 |
(0.006758 * ((hgt)^2)) - (2.247 * (hgt)) + 187.6 |
|
164 to 176 |
(0.001783 * ((hgt)^2)) - (0.6303 * (hgt)) + 56.24 |
|
176 to 183 |
0.54 |
|
> 183 cm |
NA |
|
Parameter |
Finding |
Likelihood Ratio |
|
week gestation |
< 37 |
NA |
|
|
37 weeks |
1.23 |
|
|
38 weeks |
0.91 |
|
|
39 weeks |
0.84 |
|
|
40 weeks |
0.89 |
|
|
41 weeks |
1.01 |
|
|
42 weeks |
1.42 |
|
|
43 weeks |
NA |
|
gender of fetus |
unknown |
1 |
|
|
male |
1.20 |
|
|
female |
0.81 |
Step 1: Estimate pretest probability of the woman having a cesarean section, in percent.
Step 2: Determine background odds.
background odds of cesarean section =
= (percent cesarean section) / (100 - (percent cesarean section))
Step 3: Calculate posterior odds for the cesarean section.
posterior odds =
= (background odds) * (LR maternal age) * (LR maternal height) * (LR week gestation) * (LR gender fetus)
Step 4: Convert posterior odds to estimated risk.
estimated risk =
= (posterior odds) / (1 + (posterior odds))
Specialty: Obstetrics & Gynecology
ICD-10: ,
