Spontaneously resorbing ectopic pregnancy: preservation of human chorionic gonadotropin bioactivity despite declining steroid hormone levels

Regulation of early gestational corpus luteum function in spontaneous and follicular stimulated conceptions

OBJECTIVE

To determine the regulatory role of hCG on P secretion in normal and abnormal (abortive and ectopic) first trimester pregnancies.

STUDY DESIGN

The number of doublings of hCG per day (1/DT; reciprocal of hCG doubling time) was correlated with serum P using linear and nonlinear models in normal intrauterine pregnancies, spontaneous abortions, and ectopic pregnancies (EPs) conceived spontaneously or after clomiphene citrate (CC).

RESULTS

Linear correlations between P and 1/DTs of hCG were poor. In contrast, nonlinear modeling with a hyperbolic curve fit the data well and allowed all of the data to be included for analysis regardless of the pregnancy type. Furthermore, this model could be used to explain the differential P concentrations seen in normal and abnormal first trimester pregnancies. The nonlinear hyperbolic model demonstrated that follicular events determine the maximal P production during early gestation. Human chorionic gonadotropin 1/DTs approximately equal to 0.5 sustain maximal P production. Progesterone production is then sustained by the rate of change of hCG.

CONCLUSION

Nonlinear correlation analysis suggests that P production in early gestations is regulated by prior follicular events and the rate of hCG production.

Corpus luteum function in early pregnancies is primarily determined by the rate of change of human chorionic gonadotropin levels

Regulation of human corpus luteum activity was studied with radioimmunoassays and bioassays of sera drawn serially from women suspected of having ectopic pregnancies. Progesterone values exhibited considerable overlap in pregnancies that were subsequently classified as normal intrauterine (n = 21), ectopic (n = 35), or spontaneous abortion (n = 14). The rate of change of human chorionic gonadotropin concentration was significantly correlated with progesterone levels in ectopic (r = 0.64) and all pregnancies (r = 0.70). There was no correlation (r = -0.18) between the rate of change of human chorionic gonadotropin and the bioactivity produced per volume of serum. Ectopic pregnancies and normal intrauterine pregnancies did not differ in their ratio of in vivo bioactivity to immunoactivity. From these data we conclude that corpus luteum activity is primarily regulated by the rate of change of human chorionic gonadotropin concentration, without the involvement of other serum factors. We also conclude that reduced corpus luteum function in ectopic pregnancies is not a result of biochemical modification of the human chorionic gonadotropin molecule. Finally, we discourage the use of single progesterone values in screening for ectopic pregnancies because of the considerable overlap in progesterone values among these and normal intrauterine pregnancies.