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Diagnosis of early ectopic pregnancy by measurement of the maternal serum to cul‐de‐sac fluid β‐hCG ratio

In patients suspected of having an ectopic pregnancy, because of a positive β‐human chorionic gonadotropin (β‐hCG) test and a sonographically undetectable gestational sac, even laparoscopy cannot always achieve a precise diagnosis, when the gestational age is very early. This means that the patient has to be followed by repeated β‐hCG measurements and repeated laparoscopy, which are expensive and inconvenient for the patient. This paper reports on a method that is simple to perform and that will provide the clinician with valuable information about the strong likelihood of a tubal pregnancy when ultrasound and β‐hCG measurements raise the suspicion but are not diagnostic. A prerequisite for this approach is the availability of a minimal volume (1–2 ml) of peritoneal fluid in the pouch of Douglas. A total of 131 patients who had a positive β‐hCG test and an undetectable gestational sac within the uterine cavity and who had a small volume of cul‐de‐sac fluid were studied. The fluid was obtained transvaginally by means of an ultrasound‐guided automatic puncture system. The β‐hCG level was determined in the cul‐de‐sac fluid and in the maternal serum, for comparison. In two cases with tubal pregnancy, concentrated viscous blood samples were aspirated and β‐hCG concentrations could not be measured for technical reasons. In 129 cases, the ratio of levels of β‐hCG between serum and cul‐de‐sac fluid could be measured. In 42 out of 44 patients with intrauterine pregnancy, the ratio was greater than unity; in 82 out of 85 patients with a tubal pregnancy, the ratio was less than unity. With this ratio used for detection of tubal pregnancy, the diagnostic sensitivity of the test was 95.4% and the specificity was 95.2%. The positive predictive value was 97.6% and the negative predictive value 91.3% We conclude from these findings that the measurement of the maternal serum to cul‐de‐sac fluid β‐hCG ratio facilitated the early diagnosis of an ectopic pregnancy in the Fallopian tube. Copyright © 1995 International Society of Ultrasound in Obstetrics and Gynecology