BLOOD PREGNANCY TEST
Summary: After the union of the sperm and egg cell (conception), the embryo begins to secrete Beta hCG hormone. Beta HCG test is also known as “blood pregnancy test”. While this test is at the level of 0-5 mlU/ml in non-pregnant women, it gradually increases during pregnancy. Even a very small pregnancy can be detected with this test. By monitoring this hormone level, the course of pregnancy can be determined.
Human chorionic gonadotropin (HCG) hormone It is known as the pregnancy hormone. HCG is heterodimeric, consists of alpha and beta subunits and is in glycoprotein structure. The alpha subunit is similar to the alpha subunits of LH, FSH, TSH hormones, but the beta subunit is unique. For him, beta HCG is measured, which is unique as a pregnancy test. It is an analogue of luteinizing hormone (LH) secreted from the pituitary gland in men and women. Because of its similarity to the LH hormone, HCG can be used to trigger ovulation in the treatment of infertility.
HCG hormone is a hormone produced by the developing embryo at the time of conception and then by the syncytiotrophoblast cells in the placenta.
Function of HCG Hormone
Women cannot produce the HCG hormone under normal conditions. Cells around the embryo produce the hormone HCG. This hormone continues the secretion of the progesterone hormone secreted from the ovaries and ensures that the embryo is embedded in the inner wall of the uterus (implantation).
Normally, after ovulation, progesterone is secreted from the corpus luteum formed in the ovaries, and if there is no pregnancy, the corpus luteum regresses, progesterone falls and the inner layer of the uterus is shed. HCG hormone secreted from the cells around the embryo during pregnancy, binds to special receptors in the corpus luteum and prevents the corpus luteum from shrinking, so the thickening of the uterine wall continues due to the continuation of progesterone production, and the implantation of the embryo is ensured. and by providing androgen synthesis, it ensures the development of the sex organs of the embryo.
Determination of Beta HCG Positivity
If the BhCG level is greater than 5 mIU/ml in any pregnancy, the pregnancy test is considered positive. BhCG can be determined by blood or urine testing. During pregnancy, the level of BhCG doubles every 72 hours. BhCG is positive in the blood test approximately 11 days after conception, and positive in the urine test after an average of 12-14 days. After that, it doubles every 72 hours. While the hCG level reaches its peak in the 8th and 12th weeks of pregnancy, it gradually decreases in the rest of the pregnancy. If the risk of miscarriage is detected, BhCG level should be checked every 72 hours to follow the development of the embryo. In the case of an ectopic pregnancy, low BhCG levels are detected.
In women taking HCG for infertility treatment, pregnancy testing should not be done earlier than 14 days after hCG administration. Because this period is the time for the HCG hormone to be cleared from the blood, which is done to crack the egg in the treatment of infertility. If done early, false positive results can be obtained.
Beta hCG Levels in Pregnancy
Average BhCG levels (reference values) according to weeks of gestation after the last menstrual period in women with regular menstrual cycles and a single pregnancy:
3 Weeks: 0-5 mIU/ml
4 Weeks: 5-426 mIU/ml
5 Weeks: 18-7340 mIU/ml
6 Weeks: 1080 – 56500 mIU/ml
7/8 Weeks: 7650 – 229 000 mIU/ml
9/12 Weeks: 25700 – 288 000 mIU/ml
13/16 Weeks: 13 300 – 254 000 mIU/ml
17/24 Weeks: 4060 – 165 400 mIU/ml
25/40 Weeks: 3640 – 117 000 mIU/ml
Beta hCG level decreases below 5 mIU/ml 4-6 weeks after birth.
BhCG is less than 5 mIU/ml in non-pregnant women and less than 9.5 mIU/ml in postmenopausal women.
High Beta HCG Levels
Higher than expected levels of the hormone BhCG may be detected due to a multiple pregnancy, molar pregnancy (grape pregnancy), or an incorrectly calculated pregnancy date.
Low Beta HCG Levels
Low HCG levels can be detected in cases of miscalculation of the gestational date, empty gestational sac without embryo development, and ectopic pregnancy.
Beta HCG Levels at Risk of Miscarriage in Early Pregnancy
If the beta HCG level gradually decreases in the first trimester, the probability of miscarriage in the embryo arises; A miscarriage can most often occur within the first 14 days after conception, which is the implantation period of the embryo. Since embryo implantation will be completed after 14 days, the probability of miscarriage suddenly decreases. After the miscarriage, the BhCG level drops to the normal non-pregnant level within six weeks. If the BhCG level still has not decreased to normal at the end of this period, the uterus may not be fully emptied and the placental part may remain. D/C should be repeated after ultrasonic examination again. After the first trimester. Since the placenta takes over the production of BhCG, the probability of miscarriage is very low.
Kiss. Dr. Kutlugul Yuksel
Gynecology and Obstetrics Specialist
(Article Written Date: 01.12.2011)