Laboratory-measured pregnancy rates and their determinants in a large, well-described adult cohort.
OBJECTIVE
To measure the pregnancy rate directly, to describe the characteristics of women who become pregnant, and to identify the predictors of pregnancy. No recent studies have estimated population pregnancy rates using objective, laboratory-based criteria. Furthermore, none have characterized predictive factors of pregnancy.


METHODS
Population-based prospective cohort study of 5578 women, ages 18 to 44, on active duty at Fort Lewis, Washington, from 1995 to 1997. Main outcome measures were standardized pregnancy incidence rate and predictive factors for pregnancy.


RESULTS
In the cohort, 887 pregnancies and 597 births occurred during the study period. The age- and race-standardized pregnancy rate was 108.1 per 1000 person-years. When compared with the 1995 U.S. population, the pregnancy rate ratio was 1.05 (95% confidence interval, 0.96-1.14). Factors that significantly affected the likelihood of pregnancy included age (=0.87/year), marital status (3.0, married versus single), race (1.2, African American versus Caucasian), Pap smear during study period (0.6), educational level (1.8, graduate training versus high school), and at least one prescription for oral contraceptives during the study period (0.8).


CONCLUSIONS
Standardized pregnancy rates in the study population were statistically indistinguishable from United States estimates. Use of health care services was an important independent determinant of pregnancy occurrence.
Department of Preventive Medicine, Madigan Army Medical Center, Tacoma, WA 98431, USA.
Andrew R
AR
Wiesen
Jeffrey D
JD
Gunzenhauser
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001723:Birth Rate; D015331:Cohort Studies; D005260:Female; D006772:Hospitals, Military; D006801:Humans; D015994:Incidence; D008423:Maternal Age; D008889:Military Personnel / Q000706:statistics & numerical data*; D009775:Obstetrics and Gynecology Department, Hospital; D011247:Pregnancy; D018873:Pregnancy Rate; D011258:Pregnancy Tests; D015995:Prevalence; D011446:Prospective Studies; D014861:Washington