About Pregnancy
Introduction
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.
Clearview HCG
is sensitive to 25 mIU/ml hCG in urine samples.
Why Test for Pregnancy?
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. Some 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 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.
Clearview HCG is
sensitive to 25 mIU/ml hCG in urine samples.
Why Test for Pregnancy?
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. Some 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 Clearview HCG.
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 patients. 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. Clearview
HCG 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.
Useful links:
www.ObGynWorld.com
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
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37(6), 773-778.
5. Lau H.L., Lawrence K.W., Linkins S.E. & Jones G.S. (1978)
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(1972) Human Chorionic Gonadotropin Amino Acid Sequence of the
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8. Hussa R.O. (1987) The Clinical Marker hCG. Praeger, New
York.
9. Strickland T.W. & Puett D. (1981) Contribution of
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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.