If a woman has sex on Day 0, when does the home pregnancy test give an accurate reading? Day 10? 20? Most of what I can find online talks in terms of “the missed period”, but that’s less helpful in the particular case in question.
Details:
My friend has been depressed lately and has been highly irregular about using her birth control (patch). She and her partner have been having (otherwise) unprotected sex weekly despite this :smack: , and she’s noticed vomiting in the morning, frequent urination, and related issues every day of the past week. Unfortunately her period has been very irregular of late; that’s what happens when you misuse hormonal birth control, i guess. Her last period was a little over 3 weeks ago, but was “light”, so she doesn’t think it was real. Assuming she took a test a few days from now and it came back negative, i’m wondering what time period it would be diagnostic for.
A “light period” can be implantation bleeding, but that tends to be more spotting than like a real period. If she’s really concerned about getting a false negative she should see her doctor for a blood test ASAP.
This US government site says some boxes their product can claim to show results a day after a missed period, but that a week after should be good. And I agree, being irregular about how you use hormonal birth control can really mess with your periods.
The blood tests at the doctor’s office can detect pregnancy by 6-8 days after ovulation.
Her problem, of course, is that she’s not sure when ovulation or perhaps even when her period is supposed to be. At this point, going to the doctor may be the best option.
Yeah, no chance I’ll be able to get her to go to a doctor for awhile. I’ll see if i can persuade her to try a home test in another week or two, that should be long enough.
Home pregnancy tests check for HCG levels, which double every couple of days after pregancy (specifically, implantation of a fertilized ovum).
It’s a qualitative test, meaning that it returns either a positive or a negative result–not an absolute value. Manufacturers can set various sensitivites, typically from 15 to 25 mIU but sometimes lower or higher–i.e. 6.5 to 50 mIU: http://www.fertilityplus.org/faq/hpt.html
“An October 2001 JAMA article (JAMA. 2001;286:1759-1761) said the highest possible screening sensitivity for an hCG-based pregnancy test conducted on the first day of a missed period is 90 percent, as 10 percent of women may not have implanted yet. The authors estimate that the highest possible screening sensitivity of a home pregnancy test by one week after the first day of the missed period is 97 percent.”
Note that the whole idea of “last period” and “missed period” goes right out the window for those with irregular menses and intermittent spotting.
Every pregnancy has a variable response in the rise of HCG, so no mechanism or level is perfect. If a blood test is done for a quantitative HCG–the actual level–then a more reliable method is to repeat the level within a few days and see if the HCG is rising. It is for this reason that the doctor’s office may be more accurate by using a quantitative HCG series (plus they are probably more adept at using a qualitative test if that’s used, and of course they also have the advantage of it being a day or two after the woman last tested herself, so the HCG level is higer). In addition, if a blood test returns a value of 15, say, the doctor’s office is going to say you might be pregnant, and repeat it in a week or so. A home pregnancy test set to 25 would have just said, “negative.”
Very sensitive home pregnancy tests might detect a pregnancy within about 8 days of ovulation. Note that many fertilizations–perhaps half–don’t end up with a long-term successful implantation, so for this reason it’s not especially useful to make home pregnancy tests very sensitive.
Pregnancy is “period based” rather than “sex based” in terms of timing. The times that the egg is available for fertilization and implantation are based on her period, when she ovulates and such. It doesn’t really matter when you have sex, just as long as there is sperm active when the egg is ready to be fertilized.
This is why all pregnancy related dates key off of the woman’s period, and not the date she had sex.