Dr. Marjorie Greenfield
Specializing in pregnancy and birth.
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 Ask Dr. Greenfield
Accuracy of Very Early Pregnancy Testing | | | QUESTION | | | Dear Dr. Greenfield,
How many days from conception does it take for a blood pregnancy test to be positive? Not a quantitative HCG blood test, but a blood test that shows a plus or minus sign or two lines that is similar to a urine test. Do these types of blood tests detect the hormone in your body any faster than some of the over the counter urine tests available today? For example, I am seven to eight days from ovulation (I have been trying to conceive for several months now), and I saw the dip in my temperature on Thursday morning. I also have one of those clearplan easy fertility monitors and it showed my LH surge Wednesday morning. I am guessing I probably ovulated sometime Thursday night. I went and had a blood test this morning at a clinic. It was NOT a quantitative HCG test but just a test that looked like a urine test that would tell you yes or no if you were pregnant. It was negative.— Trent's Mom in Charleston, WV | | | ANSWER |
April 11, 2002 | | | Dear Trent's Mom,
When you are trying to get pregnant, each week you're waiting can feel like a whole month. Although it is always tempting to do a pregnancy test as early as possible to get an answer, there are two reasons not to run a test so early. One is the issue you are asking about--tests can be falsely negative when run as early as you did. So I wouldn't totally rule out the possibility that you are pregnant this cycle. The other is that a test also can be falsely positive, called a chemical pregnancy, giving you false hope and unnecessary grief.
There really aren't medical reasons to find out so early whether you are pregnant. While you might think that you need to change some behaviors (like stopping drinking or starting folate) as soon as you know you are pregnant, it is actually a good idea to be doing these things while you are trying to conceive. So there isn't that much benefit to finding out about pregnancy really early, and there are the two reasons I explained above not to. A home urine test after your period is late should be adequate.
Two fertile people who are trying to conceive have about a 30 percent chance each month of getting pregnant. Try to focus on the big picture--tell yourself that you would like to be pregnant by four or six months from now, and try to disengage from the moment-to-moment obsession so that you don't drive yourself too crazy. Chances are that you will be pregnant one of these months. Good luck!— by Marjorie Greenfield, M.D. |
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