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Pregnancy Test

HCG is a hormone, produced by placental tissue. 
  • Shortly after implantation of a fertilized ovum in the uterine lining, HCG begins to be produced.
  • Levels of HCG approximately double every 2-3 days in a normal pregnancy.
  • By the time of the first missed menstrual period, pregnancy tests are usually positive (with a sensitivity of 30-35 mIU/ml).
  • Following a miscarriage, HCG levels initially fall quickly, then more gradually, until levels return to normal. This process takes, on average, about a month.

Urine is normally used for the test. A morning urine is more sensitive (in borderline situations) because it is more concentrated.

Serum can be used, and is equally reliable.

Elevations caused by:

  • Pregnancy
  • Gestational Trophoblastic Disease

Decreases caused by:

  • Miscarriage (spontaneous or induced)
  • Following obstetrical delivery
  • With resolution of an ectopic pregnancy

Normal Values:

  mIU/ml IU/L
Non-pregnant Negative <24

Pregnant

 Positive >25

 


Positive Pregnancy Test
Source: Operational Medicine 2001,  Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300