This usually refers to biochemical tests that, in conjunction with appropriate history and clinical examination, can confirm pregnancy. Most tests rely on detecting human chorionic gonadotropin (hCG), a hormone produced by the placenta.
Ultrasonography offers a more definite methods of assessing a viable pregnancy.
Types of Test
- See also Chorionic gonatropin for more details
- Detects human chorionic gonadotrophin (hCG) in the urine.
- Available as dipstick test.
- Immediate answer.
- Positive or negative (not quantitative).
- A weak signal can be equivocal, although most modern kits can detect at least 25 mIU.
- There is a dip in hCG levels from the second trimester onwards (the placenta takes on the role producing different hormones to sustain pregnancy), but the levels are usually still detectable with modern kit.
- Very high levels of hCG can overwhelm the antibody present in the kit, giving a false negative. This is described as the 'hook' effect, named after the shape of the graph produced from plotting signal to hCG concentration.
- Other false negatives may result from mutations/variants of hCG or the presence of gestational trophoblastic disease (rather than true pregnancy).
- Requires laboratory analysis.
- Useful in equivocal cases of suspected ectopic pregnancy. The result should double in 48 hours for a viable intra-uterine pregnancy.
- Can also be subject to 'hook' effect.
- ↑ Gronowski AM, Cervinski M, Stenman UH, Woodworth A, Ashby L, Scott MG. False-negative results in point-of-care qualitative human chorionic gonadotropin (hCG) devices due to excess hCGbeta core fragment. Clinical chemistry. 2009 Jul; 55(7):1389-94.(Link to article – subscription may be required.)
- ↑ Gronowski AM, Powers M, Stenman UH, Ashby L, Scott MG. False-negative results from point-of-care qualitative human chorionic gonadotropin (hCG) devices caused by excess hCGbeta core fragment vary with device lot number. Clinical chemistry. 2009 Oct; 55(10):1885-6.(Link to article – subscription may be required.)
- ↑ Yadav YK, Fatima U, Dogra S, Kaushik A. Beware of "hook effect" giving false negative pregnancy test on point-of-care kits. Journal of postgraduate medicine. 2013 Apr-Jun; 59(2):153-4.(Link to article – subscription may be required.)