Beta HCG "the pregnancy hormone" is produced by the cells of the implanting egg and can be produced in the absence of an embryo. Beta hCG can be detected in maternal plasma or urine by 8 to 9 days after ovulation. The chart to the right illustrates the normal rise and fall of hCG levels throughout pregnancy. hCG reaches a peak level at about 8 to 10 weeks and then declines for the remainder of the pregnancy [1].
Concentration of beta hCG
Throughout Normal Pregnancy
The "normal" ranges for the Beta hCG blood pregnancy test are shown in the table below.
Week from the Last Menstrual Period Amount of HCG in mIU/ml
3 5 -50
4 3 - 426
5 19 - 7,340
6 1,080 - 56,500
7 - 8 7,650 - 229,000
9 - 12 25,700 - 288,000
13 - 16 13,300 - 254,000
17 - 24 4,060 - 165,400
25 - 40 3,640 - 117,000
Because of the wide variation in values, the test is not useful in establishing the gestational age of a pregnancy.
Beta hCG levels should double approximately every 2 days for the first four weeks of pregnancy [2]. As pregnancy progresses the doubling time increases. By 6 to 7 weeks gestation beta hCG levels may take as long as 3 1/2 days to double [3,4].
You can use the Beta hCG Doubling Time Calculator to calculate the doubling time of two beta hCG samples by entering the date of the blood test and the corresponding beta hCG value for that day. If the hCG level is declining the the half life of will be calculated.
REFERENCES
1. Chartier M et al. Measurement of plasma chorionic gonadotropin (hCG) and CG activities in the late luteal phase: Evidence of the occurence of spontaneous menstrual abortions in infertile women, Fertil Steril 31:134,1979.
2. Ashitaka Y et al. Production and secretion of hCG andhCG subunits by trophoblastic tissue. In Segal S (ed):Chorionic Gonadotropins. New York, Plenum, 1980 p 151.
3. Pittawy DE et al. Doubling times of human chorionic gonadotropin increase in early viable intrauterine pregnancies. Am J Obstet Gynecol 1985; 299-302.
4. American College of Obstetricians and Gynecologists. Medical Management of Tubal Pregnancy. Practice Bulletin Number 3, December 1998. Washington, D.C. ACOG, 1998
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