The hormone hCG, or human chorionic gonadotropin, is only produced in pregnancy, and is used as a marker for conception. The placenta produces hCG; it signals the ovaries to keep making progesterone, a hormone that maintains the lining of the womb and prevents menstruation from occurring. It's important for you to check your hCG levels if you are sexually active and have missed a period.
How HCG Is Tested
Qualitative and quantitative hCG testing are methods for checking hCG levels. Qualitative hCG testing relies on sensitivity to hCG; a urine sample is usually needed for this test. If you suspect that you are pregnant, perform the qualitative test. Testing kits are sold in drug stores and can be used in the convenience of your home. Qualitative hCG testing confirms or refutes pregnancy without giving numbers. In quantitative testing, the blood is evaluated for the concentration of hCG; this must be done by a medical professional.
When to Do Quantitative Testing
Quantitative hCG testing is done when a pregnancy is suspected to be high-risk. If you've had pregnancy-related difficulties in the past, your pregnancy is considered high-risk and you should get quantitative hCG testing. In a low-risk pregnancy there is usually no need to do quantitative testing. A pregnancy is low-risk when a woman is without past medical, gynecological or obstetric history. Risk factors include a past ectopic pregnancy or miscarriage, and are good reasons to do quantitative hCG testing.
The Value of Quantitative hCG Testing
Quantitative hCG testing is used in conjunction with ultrasound imaging. The hCG level and the ultrasound both provide information about the growth of a fetus. The levels of hCG will vary, depending on the gestational age of the fetus. Your quantitative hCG results will be compared to the expected hCG value for your baby's gestation age. Your hCG level can be a clue to a miscalculation in your baby's gestational age, and can help predict multiple pregnancies or an ectopic pregnancy.
The Use of Imaging Techniques
Transvaginal and transabdominal ultrasound are two types of imaging techniques used to confirm certain results provided by quantitative hCG testing. In a transvaginal ultrasound, a probe inserted into the vagina is used to view your baby; this method is more sensitive than the transabdominal ultrasound, because the probe is closer to the fetus. In transabdominal ultrasound the probe used to view the baby is placed on your belly.
Interpretation of hCG levels
The levels of hCG increase exponentially after successful implantation of the embryo in the wall of the womb; hGG levels correlate with the size and gestational age of the fetus. When blood hCG level is around 2,000 mlU/ml, a transvaginal ultrasound should show a fetus in the womb. An ectopic pregnancy, or pregnancy outside the womb, is suspected when the value of hCG is greater than 2,000 mlU/ml and pregnancy is not confirmed by the transvaginal ultasound.
Each week of pregnancy should correlate with an accepted range of hCG levels. If your hCG value is low, it can suggest a possible error in dating the pregnancy, a possible miscarriage or an ectopic pregnancy. A high or low hCG value should always suggest a possible error in dating pregnancy. Multiple pregnancy--the presence of two or more fetuses in the womb--and molar pregnancy--a disease of the placenta resulting in an abnormal mass in the womb--should also be suspected with high hCG. Molar pregnancy is not a normal healthy pregnancy, and rarely involves a growing embryo.
