The diagnosis of pregnancy requires a multifaceted approach using 3 main diagnostic tools. These are history and physical examination, laboratory evaluation, and ultrasonography. Currently, physicians may use all of these tools to diagnose pregnancy at early gestation and to help rule out other pathologies. The classic presentation of pregnancy is a woman with menses of regular frequency who presents with amenorrhea, nausea, vomiting, generalized malaise, and breast tenderness.
Several hormones can be measured and monitored to aid in the diagnosis of pregnancy. The most commonly used assays are for the beta subunit of hCG. Other hormones that have been used include progesterone and early pregnancy factor. The hCG is a glycoprotein similar in structure to follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyrotropin. It is composed of alpha and beta subunits. The alpha subunit of hCG is similar to the alpha subunit of FSH, LH, and thyrotropin. The free beta subunit of hCG differs from the others in that it has a 30–amino acid tailpiece at the COOH terminus. Free beta subunits are degraded by macrophage enzymes in the kidney to make a beta subunit core fragment, which is primarily detected in urine samples.
Currently, 4 main hCG assays are used: (1) radioimmunoassay, (2) immunoradiometric assay, (3) enzyme-linked immunosorbent assay (ELISA), and (4) fluoroimmunoassay. These assays are highly specific for hCG with antibodies directed against 2 or more isotopes on the intact hCG molecule. Time of detection is related to the sensitivity of the assay being used. Most current pregnancy tests have sensitivity to approximately 25 mIU/mL. Urine devices must be formulated to detect hyperglycosylated hCG, which is the key molecule in early pregnancy.