to the editor: In the article “Diagnosis and Management of Ectopic Pregnancy”1 in the November 1, 2005, issue of American Family Physician, Drs. Lozeau and Potter suggest that serum progesterone levels detect pregnancy failure, are insensitive in diagnosing ectopic pregnancy, and that algorithms incorporating progesterone levels miss more ectopic pregnancies and require more surgeries. Although we agree that there is no specific cutoff for progesterone levels that accurately diagnose ectopic pregnancy,2 progesterone levels may still play a useful role in the evaluation and management of suspected ectopic pregnancy.
Progesterone levels may be helpful in the evaluation of suspected ectopic pregnancy if they are very high or very low. The authors quote a sensitivity of 15 percent for progesterone levels in ectopic pregnancy. Of course, the sensitivity of a quantitative test depends on the specific level selected for the cutoff, but in a meta-analysis2 of 27 studies, sensitivities ranged from 44 to 100 percent, depending on the threshold. In 12 studies with a total of 1,107 women, only 2.6 percent of women with an ectopic pregnancy had progesterone levels greater than 20 ng per mL (64 nmol per L).2 In 13 studies, only five of 1,615 women (0.3 percent) with progesterone levels less than 5 ng per mL (15.9 nmol per L) had a viable intrauterine pregnancy.2 By establishing the low likelihood of interrupting a viable intrauterine pregnancy, serum progesterone measurements may allow for the option of a dilatation and curettage to rule out an ectopic pregnancy in women with an indeterminate ultrasound examination.3 None of the studies cited by Drs. Lozeau and Potter1 incorporated progesterone measurements into a diagnostic algorithm in this way.
Serum progesterone measurements also may have a prognostic use. In women with a progesterone level below 10 ng per mL (31.8 nmol per L) and a human chorionic gonadotropin (hCG) level below 1,500 mIU per L (1,500 IU per mL), spontaneous resolution of ectopic pregnancy is more likely.4 Progesterone levels have been included in a scoring instrument designed to predict the success of expectant or medical management of ectopic pregnancy.5 In addition, serum progesterone levels fell to normal (less than 1.5 ng per mL [4.8 nmol per L]) faster than hCG levels following treatment with methotrexate or laparoscopic salpingostomy and for this reason may be a better marker for predicting successful treatment.6