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Identification of Women At Risk for Preterm Birth

Purpose: To evaluate a pregnant woman for risk of preterm delivery using the risk scoring system of Ross et al.

Description

Ross et al developed a risk scoring system based on logistic regression to identify women at risk for preterm delivery. 22 factors based on historical or current gestational data were identified as significant. Women may be identified based on a logistic score or number of risk factors present.


Patient population:

(1) Involved 8,240 patients delivering at Harbor/UCLA Medical Center in Los Angeles.

(2) The population was predominantly Hispanic.

(3) Data was collected from July, 1979 to December 1982.

 

Historic Factor

Univariate Odds Ratio

Logistic Odds Ratio

Regression Coefficient

previous induced abortion

1.64

1.309

0.269

habitual abortions

3.31

2.210

0.793

previous premature delivery

3.09

2.488

0.912

previous neonatal death

2.19

1.277

0.244

uterocervical anomaly

5.26

1.489

0.398

classic Caesarean section

2.11

1.600

0.470

previous myomectomy

46.0

22.847

3.130

chronic hypertension

2.60

1.799

0.587

previous urinary tract infection

1.38

1.107

0.101

renal disease

2.38

2.115

0.749

psychiatric hospitalization

2.41

1.380

0.322

cigarette abuse

1.78

1.374

0.318

marijuana abuse

3.30

2.072

0.728

narcotic abuse

5.58

1.905

0.645

from Table 2, page 342

 

Current Gestation (Developing) Factor

Univariate Odds Ratio

Logistic Odds Ratio

Regression Coefficient

size-date discrepancy

1.46

1.393

0.331

severe anemia

2.51

2.165

0.772

threatened abortion

4.30

4.134

1.420

incompetent cervix

24.34

12.527

2.528

surgery requiring hospitalization

2.20

1.900

0.642

multiple gestation

9.44

6.755

1.190

pre-eclampsia, mild

2.37

1.705

0.534

bleeding after 20 weeks

5.89

5.321

1.672

from Table 2, page 342

 

logistic score =

= SUM(regression coefficients for historic factors present) + SUM(regression coefficients for developing factors present) + (constant )

 

where:

• constant = -3.193

 

number of risk factors =

= SUM(individual risk factors present)

 

Interpretation:

• minimum score: -3.193

• logistic score cutoff: -2.875. If the score is > -2.875, then the woman is at risk for preterm delivery.

• The number of risk factors present is associated with increased risk of preterm delivery, with the risk increasing as the number of risk factors increase.

 

Individual risk factors:

(1) 4 of the factors are not associated with high risk by themselves: history of previous induced abortion, cigarette use, previous urinary tract infection, and previous neonatal death. The presence of 2 or more of these factors places the person at high risk.

(2) The presence of any one of the remaining 18 factors indicates that the person is at high risk.

 

Performance:

• 89% of women delivering at <= 28 weeks of gestation were identified

• 79% of women delivering at <= 32 weeks gestation were identified

• only about 56% of women delivering at <= 37 weeks gestation were identified

• Performance better for multipara and multigravid women.

• Specificity improved as the number of risk factors increased, but the sensitivity decreased.


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Specialty

Objective

ICD-10