HCG Levels During the First Trimester
When you first become pregnant your HCG levels will begin to rise drastically. The body produces the hormone when you conceive and the levels usually double every couple days. The increasing levels of this hormone serve to prevent menstruation and protect the pregnancy. As long as hCG is increasing at a normal rate then the pregnancy is viable. However, if the levels are increasing very slowly or even decreasing then it is almost definite the pregnancy is not viable.
When you take a pregnancy test, whether over the counter or at your doctors office, the test is looking for this hormone. A specific level of the hormone is necessary for a positive test. Generally, the urine tests are just qualitative and only determine if there is a certain level of hCG present in the urine. Quantitative tests are measured through blood tests to determine if the pregnancy is progressing as it should with the hCG levels increasing as they should. Many times low risk pregnancies do not require a quantitative test of hCG levels. However, individuals at risk for ectopic pregnancy or miscarriage may need to be tested this way to check on the pregnancy.
Generally, by the time you miss your period there is enough hCG in your urine to react positively with a home pregnancy test. A blood test might be positive a bit sooner, but generally not too much. However, if you take a home pregnancy test and receive a negative result but still believe you might be pregnant just wait a couple days and try again. Some women are less pregnant than they believe they are due to late ovulation so they may actually be pregnant but not as pregnant as they believe. Women who have a positive test one day and then a negative test the next day probably will miscarry because pregnant tests may give false negatives but never false positives because it reacts with the hCG in the urine.
If a quantitative test reveals levels of hCG at 2,000 or more then the fetus should be visible on the ultrasound. If the levels are 2,000 and no fetus is visible there is a high probability for an ectopic pregnancy.
While hCG levels increase rapidly during the first 12 weeks of a normal pregnancy they then begin to ease off and remain fairly steady for the rest of the pregnancy. Knowing about hCG levels during your first trimester will help you better understand how pregnancy progresses and how pregnancy tests actually work.