Design 2 cohort studies: 1 for derivation and 1 for validation of the clinical prediction model results. Setting The emergency department of a tertiary care, military, teaching hospital in San Diego, California, USA. Patients Women who were haemodynamically stable and had abdominal pain or vaginal bleeding in die first trimester of pregnancy. Exclusion criteria were previous documentation of an intrauterine pregnancy (IUP) on pelvic ultrasonography, enrolment in die prospective clinical data registry on a previous visit to the emergency department, or estimated gestational age and corresponding uterine size of & 13 weeks. 486 women (mean age 25 y, mean gestational age 58 d) formed the derivation cohort, and 429 women (mean age 25 y, mean gestational age 58 d) formed the validation cohort. Description of prediction guide The clinical prediction model classified pregnant women into 3 groups according to risk. High risk women had signs of peritoneal irritation or definite cervical motion tenderness; intermediate risk women had no fetal heart tones by handheld Doppler, no tissue visible at the cervical os, and pain (oilier than midline suprapubic cramping) or tenderness (any cervical motion, uterine, or adnexal tenderness); and low risk women did not meet high or intermediate risk criteria. Main outcome measure Diagnosis of an IUP or ectopic pregnancy. Main results In the derivation cohort, 58% of women had a viable IUP, 34% had a non-viable IUP, and 8% had an ectopic pregnancy. In the validation cohort, 62% of women had a viable IUP, 30% had a non-viable IUP, and 7.2% had an ectopic pregnancy. Sensitivities, specificities, and likelihood ratios are shown in the table. Conclusion In women with abdominal pain or vaginal bleeding in the first trimester of pregnancy, the' high risk criteria of a clinical prediction model had high specificity but low sensitivity and the intermediate risk criteria had high sensitivity but low specificity for predicting ectopic pregnancy.
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