Cluster 175: beta chorionic gonadotropin hcg negative human test potential childbearing pregnancy Cluster 858: menopausal sterilization bearing post child beta hcg potential surgical previous Cluster 982: chorionic hcg gonadotropin beta human pregnant women positive serum test Cluster 1025: hcg iu units sensitivity chorionic gonadotropin minimum test equivalent pregnancy Cluster 2355: beta pregnancy pregnant subject established hcg chorionic result confirmation gonadotropin