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Your Pregnancy Test
Your doctor will request a blood pregnancy test 12 to 14 days after infertility treatment. This test measures Human Chorionic Gonadotropin hormone (hCG). HCG is secreted by the developing placenta shortly after a fertilized egg has implanted in the uterine lining. The appearance of hCG soon after conception — and its subsequent rise in concentration during early gestational growth — make it an excellent marker for the early detection of pregnancy. A blood measurement of hCG is more accurate than a urine test because hCG is detectable in blood sooner than in urine. This type of blood test is called a beta hCG test (often referred to as a “beta”); it measures the exact units of hCG in the blood.
The hormone in the hCG injection that is given to stimulate ovulation in assisted reproductive technology (ART) treatment is the same as the hCG that is being measured for pregnancy. After receiving an hCG injection, depending on the dose and the individual woman, the hormone takes approximately 5 to 14 days to clear the system. Therefore, the pregnancy test should not be drawn prior to 12 to 14 days after an hCG injection, to avoid a “false positive” result.
Blood tests with levels less than 5 mIU/ml are considered negative, and generally levels greater than 25 mIU/ml are considered positive; however, labs have different standards as to what they consider positive. Therefore, it is best to have repeat blood tests performed at the same lab. If elevated, the average hCG levels double approximately every two days until approximately six weeks, then double every three days when the level is 1600 to 6000; then the doubling slows to every four days or so. Levels peak a week or two before the end of the first trimester of pregnancy (12 weeks) and decline in the second trimester.
Many doctors will do two or three hCG level tests to confirm doubling and stop there. Others stop after a fetal heartbeat is detected. After a heartbeat is seen or heard, the chance of miscarriage drops to 16 percent before 6 weeks of conception, 5 percent from 7 to 9 weeks, 1 percent to 2 percent after 11 weeks.