Use of beta-human chorionic gonadotropin in gestational aging

Quantitative radioimmunoassay (RIA) of the beta chain of human chorionic gonadotropin (B-hCG) in serum has been used to evaluate the gestational status of 99 normal early pregnancies in contrast to 29 ectopic, threatened, aborted and/or terminated cases. Quantitative measurement of serum B-hCG-RIA standardized against the second international standard (2dIS) accurately established age of normal pregnancies in utero up to but not after three weeks postconception and with an accuracy of plus or minus four days between the third and eighth week of gestation. Quantitative urinary hCG-RIA standardized against the 2dIS were not useful for gestational aging. Useful serum hCG-RIA were identically linear and parallel with the 2dIS, had negligible crossreactivity with LH, FSH and/or TSH, and had low nonspecific binding. Of 13 hCG-RIA evaluated, only assays having these latter characteristics were able to detect ectopic pregnancies, spontaneous abortions, and/or threatened pregnancies with up to 90 percent accuracy. However, some assays not standardized to the 2dIS gave over 200 percent error in hCG serum values. Thus, correct choice of quantitative B-hCG reagents is necessary for early pregnancy assessment.