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Pregnancy tests are based on the detection of elevated levels of
human Chorionic Gonadotrophin (hCG) in serum or urine, which is
produced by the developing placenta following
implantation1,2. Urine and serum samples of
non-pregnant females usually contain less than 5 mIU/ml
hCG3. After conception levels of hCG in a normal
pregnancy will increase rapidly with levels reaching between
100,000 – 200,000 mIU/ml at the end of the first
trimester1,2,4,5,6. The appearance and rapid rise in the
level of hCG makes it an excellent marker for pregnancy.
HCG is a dimeric glycoprotein hormone consisting of an alpha
and beta subunit. The alpha subunit is common to Follicle
Stimulating Hormone (FSH), Luteinising Hormone (LH), Thyroid
Stimulating Hormone (TSH) and hCG. The beta subunit is specific to
each hormone and is responsible for its biological
activity7,8,9 The development of antibodies to the beta
subunit of hCG allows reliable measurement of this hormone with no
cross reactivity with the other glycoprotein hormones.
The Function of hCG During Pregnancy
Pregnancy begins with fertilisation of the egg and
implantation of the fertilised egg in the lining of the uterus.
Implantation will normally occur during the week following
ovulation. hCG begins to be produced around the time of
implantation8.
A pregnancy will usually only continue after implantation if
menstruation is prevented. Estrogen and Progesterone are produced
by the corpus luteum and prevent menstruation by maintaining the
lining of the uterus. The corpus luteum itself is maintained by hCG
that is produced by the trophoblast cells of the fertilised
ovum.
Levels of hCG are considered to be identical in both serum and
urine10,11. HCG levels increase rapidly in the first
stages of pregnancy and will normally begin to appear in the blood
and subsequently in the urine of the pregnant woman a week after
conception. By the day the period is due hCG levels of
approximately 50 - 250 mIU/ml are expected1,2,4,5,6.
During the first trimester, levels of hCG should double every 48-
72 hours peaking between 100,000 – 200,000 mIU/ml at the end of the
trimester, thereafter levels of hCG drop dramatically with levels
remaining well above the basal level throughout the
pregnancy.
TestPack hCG Combo is sensitive to 25
mIU/ml hCG in both urine and serum samples.
Why Test Early?
During the early stages of pregnancy, the foetus is extremely
susceptible to influences from its external environment. Medical
professionals believe that certain measures should be taken to
ensure the best possible chance of the baby being healthy at
birth.
In a hospital environment testing early for pregnancy allows the
mother to avoid exposure to other hazards such as x-rays, chemicals
and medication.
Some infections are more serious in pregnant than non-pregnant
women because of the risk they may pass across the placental or
amniotic barriers. SSome examples of these are Rubella,
Toxoplasmosis, syphilis, Listeriosis and Cytomegalovirus. Testing
early for pregnancy may allow for the mother to test for immunity
to rubella which can cause severe congenital defects or to avoid
foods that might harbour Listeria monocytogenes that could
cause spontaneous abortion16,17.
Smoking can reduce the level of oxygen and nutrients reaching the
foetus and increase the levels of nicotine in the blood. This
increases the risk of spontaneous abortion, developing placental
complications and giving birth to low weight babies. Alcohol intake
during pregnancy can cause growth defects, central nervous system
impairment and facial deformities in the foetus as well as
increasing the risk of spontaneous abortion11. Early
detection of pregnancy is therefore useful to avoid putting the
foetus at risk by smoking and drinking alcohol.
Research has shown that the incidence of neural tube defects such
as spina bifida and hydrocephalous can be greatly reduced by taking
folic acid supplements both before and during
pregnancy12. Many countries recommend an intake of 0.4mg
of folic acid per day prior to and during the first stages of
pregnancy18. In addition there are certain foods that
should be avoided during pregnancy. Foods which contain high levels
of vitamin A should be avoided as it has been shown to be
teratogenic14. Excessive intake of vitamin D and
caffeine should also be avoided15. Testing early for
pregnancy can therefore help to plan a healthy balanced diet during
pregnancy.
Environmental causes of foetal malformations account for
approximately 10% of malformations, with less than 1% related to
prescription drug exposure, chemicals or
radiation18.
Elevated hCG levels in non-pregnant individuals
There are a number of medical conditions other than
pregnancy that cause elevated levels of hCG and these may cause
false positive results with TestPack hCG
Combo.
Gestational trophoblastic diseases can result in partial or
complete hydatiform moles (cystic trophoblast tissue from a
non-viable pregnancy) or choriocarcinomas (proliferation of
trophoblastic tissue in the maternal tissues). Hypersecretion of
hCG is common to all conditions19,20. It is also known
that non-trophoblastic neoplasms can hypersecrete hCG. Braunstein
(1980) reported that immunoreactive hCG is found in the sera of
approximately 20% of cancer patients21. It is important
to remember that trophoblastic disease and non-trophoblastic
neoplasms may produce altered forms of hCG and different
proportions of alpha and beta forms8.
TestPack hCG Combo is a qualitative test for
the detection of intact hCG and is not intended for the diagnosis
of these conditions, although these conditions may give positive
results.
References
1. Braunstein G.D., Rasor J., Adler D., Danzer H.
& Wade M.E. (1976) Serum human Chorionic Gonadotrophin
levels throughout normal pregnancy. Am. J. Obstet. Gynecol.
126(6), 678-681.
2. Chard T. (1992) Pregnancy test – a review. Human
Reproduction. 7(5), 701-710.
3. Alfthan H., Hagland C., Dabek J. & Stenman U.H. (1992)
Concentrations of human Chorionogonadotropin, its b -subunit,
and the core fragment of the b -subunit in serum and urine of men
and non-pregnant women. Clin. Chem. 38(10), 1981-1987.
4. Lenton E.A., Neal L.M. & Sulaiman R. (1982) Plasma
concentrations of human Chorionic Gonadptrophin from the time of
implantation until the second week of pregnancy. Fertil.
Steril. 37(6), 773-778.
5. Lau H.L., Lawrence K.W., Linkins S.E. & Jones G.S. (1978)
Early detection of human Chorionic Gonadotrophin in urine by
simple immunoassays. Am. J. Obstet. Gynecol. 132(6),
691-693.
6. Hsu M.I., Kolm P., Leete J., Dong K.W., Mausher S. &
Oehninger S. (1998) Analysis of implantation in Assisted
Reproduction through Use of Serial hCG Measurements. J.
Assisted Reprod Genetics. 15(8) 496-505.
7. Bahl O.P., Carlsen R.B., Bellisario R. & Swaminathan N.
(1972) Human Chorionic Gonadotropin Amino Acid Sequence of the
Alpha and Beta Subunits. Biochem. Biophys. Res. Commun. 48,
416-422.
8. Hussa R.O. (1987) The Clinical Marker hCG. Praeger, New
York.
9. Strickland T.W. & Puett D. (1981) Contribution of
Subunits to the Function of Luteinising Hormone/Human Chorionic
Gonadotrophin Recombinants. Endocrinology. 109,
1933-1942.
10. Kent A., Kitau M.J. & Chard T. (1991) Absence of
Diurnal Variation in Urinary Chorionic Gonadotrophin Excretion At
8-13 Weeks Gestation. B J Obstet. Gynaecol. 98.
1180-1181.
11. Cogswell M.E., Weisberg P. & Spong C. (2003) Cigarette
Smoking, Alcohol use and Adverse Pregnancy Outcomes: Implications
for Micronutrient Supplementation. J. Nutr. 133,
1722S-1731S.
12. Czeizel A.E. (2000) Primary prevention of neural-tube
defects and some other major congenital abnormalities:
recommendations for the appropriate use of folic acid during
pregnancy. Paediatric Drugs. 2(6), 437-49.
13. Egen V. & Hasford J. (2003) Prevention of neural tube
defects: effect of an intervention aimed at implementing the
official recommendations. Soz Praventivmed. 48(1),
24-32.
14. Bendich A. & Langseth L. (1989) Safety of Vitamin A. Am
J Clin Nutr. 49(2), 358-371.
15. Ross M.P. & Brundage S. (2002) Preconception
counselling about nutrition and exercise. J S C Med Assoc.
98(6), 260-3.
16. Grangeot-Keros L. (1992) Rubella and Pregnancy. Pathol
Biol. 40(7), 706-710.
17. Gilbert G.L. (2002) Infections in Pregnant Women.
175(5), 229-236.
18. Brent R.L. & Beckman D.A. (1994) The contribution of
environmental teratogens to embryonic and fetal loss. Clin
Obstet. Gynecol. 37(3), 646-670.
19. Dreyfus M., Tissier I. & Phillippe E. (2000)
Gestational Trophoblastic Diseases. Classification,
Epidemiology and Genetic Data. J. Gynecol. Obstet. Biol.
Reprod. 29(7), 687-689.
20. Quinonez Zarza C. (1995) Hydatiform Mole. Clinical aspects,
incidence and risk factors. Ginecol. Obstet. Mex. 63,
391-394.
21. Braunstein G.D., Rasor J. & Wade M.E. (1980) Presence
of an hCG-like substance in non-pregnant humans. In: Chorionic
gonadotropin. Segal S.J. (ed) Plenum Press, New York, 383-409.
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