HUMAN CHORIONIC
GONADOTROPIN (hCG) |
Human chorionic gonadotropin (hCG) is a glycoprotein hormone heterodimer comprised of an a and a ß subunit. Multiple forms of hCG are typically found in blood and urine. The early placental trophoblasts produce a and ß-hCG molecules. Alpha and ß-hCG is detectable within approximately one week of implantation and then rises exponentially (initial doubling time of about 1.5-2.5 days). The cytotrophblastic cells secrete dimer hCG and the syncytial trophoblast cells secrete free alpha-hCG. There is no free beta-hCG in the placenta, but it is in blood.
·
After ovulation, if ovum is fertilized, the blastocyst implants in the endometrium
on day 21. As soon as the blastocyst implants, hCG is present in the outer syncytial layer.
· 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].
·
Then rate of secretion rises rapidly between 3
and 9 weeks after ovulation and reaches a peak about 10 to 12 weeks after
ovulation and decreases to a much lower value by 16 to 20 weeks after
ovulation. It continues at this level between 20 to 40 weeks pregnant period
and disappears in blood 2 weeks after delivery.
· Rising hCG reflects rapidly proliferating and invasive placenta.
· Falling hCG is associated with a relative reduction in trophoblasts.
Normal levels |
||
Week from the Last
Menstrual Period (LMP) |
Amount of hCG in mIU/ml (1) Mean Level |
Amount of hCG in mIU/ml (1) Range of values |
3 |
|
5 - 50 |
4 |
37 |
4 - 426 |
5 |
373 |
19 - 7,340 |
6 |
7800 |
1,080 -
56,500 |
7 - 8 |
31,800
– 72,600 |
7,650 -
229,000 |
9 - 12 |
9 wks -116,000 10 wks - 108,000 11 wks
– 87,700 12 wks
– 76,100 |
25,700 -
288,000 |
13 - 16 |
13 wks -
80,000 14 wks
– 56,600 15 wks
– 50,600 16 wks
– 37,500 |
13,300 -
254,000 |
17 - 24 |
17 wks
– 21,500 18 wks
– 24,200 19 wks
– 17,400 20 wks
– 15,700 21 wks
– 15,100 22 wks
– 14,500 23 wks
– 14,800 24 wks
– 10,600 |
4,060 -
165,400 |
25 - 40 |
25 wks
– 10,800 26 wks
–11,500 27 wks
– 13,600 28 wks
– 14,400 29 wks
– 13,700 30 wks
– 16,000 31 wks
– 12,100 32 wks
– 19,600 33 wks
– 15,200 34 wks
– 23,900 35 wks
– 24,500 36 wks
– 16,500 37 – 40
wks – 29,000 |
3,640 -
117,000 |
|
|
There are several physiological functions of hCG during pregnancy.
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 1979;31:134.
2. Ashitaka Y et al. Production and secretion of hCG andhCG
subunits by trophoblastic tissue. In Segal S (ed):Chorionic Gonadotropins.
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.
5. Lipscomb
GH, Stovall TG, Ling FW. Non surgical treatment of ectopic
pregnancy. NEJM 200;343(18):1325-1329.