The apparent late half-life of human chorionic gonadotropin (hCG) after surgical treatment for ectopic pregnancy A new approach to diagnose persistent trophoblastic activity

Abstract Objective : The disappearance kinetic of human chorionic gonadotropin (hCG) follows a biexponential decay with a rapid initial fall followed later by a slow disappearance. This kinetic is characterised by two half-lives: an early and a late. The objective of this study was to determine if and which half-life could be used clinically to detect persistent trophoblast after conservative surgery in patients with ectopic pregnancy. Design : Retrospective analysis of patients having undergone salpingostomy by laparoscopy for an ectopic tubal pregnancy between January 1990 and October 1993. Setting : Gynaecology Department of an University Hospital. Patients : 104 women with diagnosed tubal ectopic pregnancy were treated by salpingostomy performed under laparoscopy. In seven cases, persistent trophoblast was diagnosed on the basis of plateauing or increasing peripheral hCG values. Main results : From the individual disappearance curves of hCG we calculated the early half-life (early T 0.5 , from samples obtained between 0 and 48 h postsurgery) and the late half-life (late T 0.5 , from samples obtained between 2 and 7 days postsurgery). Late T 0.5 but not early T 0.5 were significantly ( P P =0.416 respectively) longer in women ( n =7) in whom a persistent trophoblast was diagnosed. Early T 0.5 was dependant on the preoperative value of hCG, whereas late T 0.5 was independent. We propose to use late T 0.5 as a parameter to follow ectopic pregnancies after treatment.