Early Pregnancy and HcG Levels
Pregnancy Test
How can the test tell if you're pregnant-what does it look for?
Pregnancy tests detect human chorionic gonadotropin (hCG), a substance produced by a developing fetus' placenta but not by adults (i.e. ordinarily hCG would not have been present in the mother). Tests done in the doctor's office or at home both detect hCG.
A home pregnancy test kit is always a urine test. It typically contains a chemically-treated dip stick.
Note: Urine from the first time the woman pees is preferable, since it is the most concentrated.
Tests performed by the health care provider are blood tests. The tests are usually qualitative (that is, they merely provide a yes or no answer).
Qualitative tests are also often the type used for screening. They may be done just to be on the safe side (in case the woman were to be unknowingly pregnant), before she takes a medication or has a procedure done that could cause birth defects in a developing baby.
Blood may be tested quantitatively, though (measuring the exact amount of hCG).
Why would the blood test have to be done instead of the quick urine test?
Advantages and disadvantages of the two types of pregnancy tests are:
URINE
Pro:
Private and Inexpensive, since no doctor's visit is required
Quick
Con:
Less accurate in early pregnancy
BLOOD
Pro:
More sensitive
Con:
More invasive (requires needle stick)
Sample must be sent off to a laboratory, thus:
More costly, and Results take longer
If I do the test at home, and it turns out to be negative, does that mean I'm definitely not pregnant?
The test is 98% accurate. Nevertheless, if the test is done too early, before sufficient levels of hCG can build up to detectable levels, results of the test will be negative despite the woman actually being pregnant. Therefore, if menstruation still has not occurred, make an appointment with your doctor for a blood test. In the meantime, if you wish, you can do another urine test after waiting a few more days.
Caution: Medications that influence hCG levels, and can thus produce false results for pregnancy tests, include:
1. Penicillin
2. Tranquilizers
Similarly, conditions which are capable of altering hCG levels are:
1. Urinary Tract Infections
2. Other causes of Blood in the Urine
3. Hepatitis
Rather than a missed period, early signs of pregnancy could be any of the following:
1. Spotting or Light Bleeding
2. Breast Tenderness
3. Nausea
4. Increase in the Frequency of Urination
5. Fatigue
6. Bloating
Note: The stomach will not protrude visibly (i.e. most women do not "show") until the second trimester (that is, for several months into the pregnancy). The baby's movements are generally felt for the first time during the second trimester, around the fourth month of pregnancy.
How soon can I do the test?
For home pregnancy testing, a woman should wait at least a week after a missed period. HCG does not even begin to be produced in substantial amounts until a day or two after implantation of the fertilized egg, which does not take place until ten days after ovulation. The hCG then needs to accumulate to a level high enough to be readily detected by the test.
The urine test can only detect hCG levels above 25-50 mIU/ml (milli-international units per milliliter).
Blood tests are five times as sensitive; they can detect levels as low as 5 mIU/ml.
How long will I have to wait to find out if I'm pregnant or not?
For a urine test the answer is ready virtually immediately (within one to two minutes).
On the other hand, getting the result back for a blood test will take at least several hours. Sometimes it will not be available until the next day.
What would the quantitative test be needed for?
Measurement of the exact amount of hCG would reveal certain atypical situations. When hCG is too high, it suggests a multiple pregnancy. On the other hand, when hCG is too low, that is indicative of a problem with the pregnancy, such as:
1. Death of the fetus, or impending loss of the baby
2. Growth of the baby outside of the womb
Note: Later on in pregnancy, even in normal circumstances hCG will decline naturally. Previously the hormone was needed to sustain the corpus luteum, for production of progesterone to maintain the uterine lining. After the placenta is well established, the hCG is no longer needed, since the placenta has taken over progesterone production.
If someone's hCG isn't high enough, what could the doctor do?
HCG levels should rise steadily throughout the first trimester. consequently, in the case of low hCG levels an ultrasound will be ordered to check for ectopic pregnancy or miscarriage.
For a finding of unusually-high hCG, the ultrasound images would tell the doctor whether or not the mother is having twins (or triplets).
Note: Ultrasound will be done even when hCG levels are normal.
The procedure is also useful for establishing how far along the pregnancy is, thus the estimated date of conception, so that the due date can be calculated.
Is there any harm in doing the test just in case?
There is no risk associated with having a urine pregnancy test (and only the remote possibility of infection for the blood test, as with any needle puncture).
