Pregnancy Tests
There have been several posts over time regarding use of home pregnancy tests, when they work and how to interpret them. Let’s begin with the physiology of a pregnancy.
Using a typical 28 day menstrual cycle, ovulation would take place on day fifteen, counting from the beginning of the last period. Theoretically, this will be the day of ovulation. Do not live by this hypothetical; women have become pregnant on every day of the cycle including during menstruation. For our purposes, let us further assume that unprotected sex occurs on this fifteenth day with a healthy dose of semen ejaculated into the vagina. There is a one in four chance of a live baby developing.
The mechanism is that sperm from that dose of semen will find its way through the cervical os. In actual practice, millions will find their way and start swimming randomly around the uterus. Some of these sperm will find their way into one or the other of the fallopian tubes – one of which (sometimes both) will be transporting a fresh egg, ready to be fertilized. It may take from a few minutes to a few days for the egg and a sperm to negotiate that he will be accepted. Only in the last decade have we determined that the egg has some decision making process and does not passively accept any sperm that presents itself. Now the egg has been fertilized, thereby becoming a blastocyst, and continues its way down the fallopian tube into the uterus. This trip and subsequent implantation can take several days – six is considered to be the maximum. The fertilized egg will begin cellular division and require nutrition. At this point, it either dies and is passed out through the vagina (women have actually seen the egg deposited in their knickers) or it implants itself into the vaginal lining and draws nutrition from the rich covering that has been built up since the last period.
When, and only when, the egg becomes implanted, the body begins to produce quantities of human Chorionic Gonadotropin – the hormone of pregnancy. It is this hCG that can be detected by pregnancy tests, BUT, it is not detectable in the bloodstream for six days nor in the urine for eight days. Production of hCG inceases rapidly and remains at a rather high level through the first trimester of pregnancy and then tapers off but continues throughout the pregnancy and lactation. It is the hCG that signals the mix of other hormones in the bloodstream to cause menstruation or retard ovulation. This is the theoretically typical situation. It will vary a bit if ovulation varies or if the sperm are delivered into the vagina a few days before or after the moment of ovulation (egg release from the ovary).
We can conclude from this description that the marker used by ALL pregnancy tests will not show up for, usually, twelve days or a bit more. Therefore, the tests do not work well before twelve to fourteenn days after unprotected sex and this will usually be after a period is late. If ovulation took place very early in the cycle, the test may work before the next period is due. Most tests’ instruction sheets will indicate accuracy “from the day your period is due.” More realistically, a few days after you expect your period.
All the tests use basically the same chemistry but their administration varies. It is important to read the instruction sheet several times and follow the instructions precisely. With some, you pee on a stick; some, pee in a cup and dip the stick; some, pee in a cup, add a few drops of reagent and dip the stick. Some change color; some have geometric patterns of lines appear; some have words appear. The key is to follow the timeline directed. Left in the urine too long, all tests will show pregnancy; too short or not completely wetted, will give a false negative.
Beware the advertising. Some tests advertise 99% accuracy the first day of a missed period. Not likely. The level of hCG is so low that it may not be detected or the indicator may be so faint as to be unreadable. “Giving it more time” is not a solution. All the tests will give a positive if left in the urine for long. That same test will be much more accurate just a day later. We have come a long way from “the rabbit died” and “the frog died” (fifty years ago, urine was injected into a female rabbit, later, a frog, and, if hCG was present, the animals ovaries went into overdrive, ruptured and killed the beast) to rather simple and private testing. That can be a long fortnight from losing control and having unprotected sex until the test is accurate.
Brandye
Replies:
I noticed the several questions as well, so thank you for this post, dear Brandye! Cool to mention the little facts too! I knew about the origins of the saying, but never really knew what the test with frogs was all about. Learned something today :)
Thing I do not understand is: how is it possible to get a positive pregnancy-test when leaving it in the urine for too long? I did notice the warning signs on the tests. It stated that results are not valuable anymore, when you leave the test and not look at the results within half an hour.. Off course I followed instructions :) But I never understood why...
And maybe this question is related to the first: I've read somewhere you could also get a positive pregnancytest when a woman is going into menopause, because of all the hormonal changes. Is this true? (Or is it, as we call it: a 'monkey-bun', meaning about the same as: 'bullshit', but in a lighter and more funny way ;))
RedRoses
Well, we all have a very low level, undetectable, level of hCG plus all sorts of other stuff in our urine. Entering menopause is entering a whole new world and anything is possible. I do not believe that false positives on pregnancy test is very common, though.
Brandye
Thanx for your answer :)
Another question, maybe an odd one: If you've had a positive pregnancy test, than start cramping/bleeding (iow probably miscarry), how long should it take for HCG-levels to be normal? And a test to become negative?
I've been active on a forum for women who have miscarried and this is a question more people are worried about and remains unanswered. Mostly worries, because women are trying to find out if it's 'really' gone... Also it makes you think: how long can you 'feel' pregnant, because of pregnancy-hormons fooling you? Or do you feel that way, because your own emotions are making you feel this way? So it really makes you hungry for information... (O yes, and I know: best thing to do is see a doctor, who can order for further testing, especially for women who have been pregnant for more than a few weeks)
I guess the answer lies somewhere in: depends on how long you've been pregnant. Most women I corresponded with were between 2-7 weeks pregnant (4-9 weeks calculated from the first day of last menstruation), so rather early miscarriages (some without even having talked to a doctor about being pregnant). Why not take that as an example?
To not set off any alarmbells: this question refers to a personal situation in the past with questions that remained unanswered. It's not like it's related to the here-and-now or to a girl in need for rescue :)
RedRoses
The home pregnancy tests only indicate the presence of hCG. We normally, not pregnant, have a range of 50-300 i.u./ml. Hence, left too long in the urine results in a false positive. After implantation, the level of hCG rises dramatically - often doubling every two days - and can reach as high as 30,000 before leveling or, even, declining. It can take more than a week after miscarriage for this level to fall to the normal range. Until the level gets back into the normal range, a home pregnancy test will show a pregnancy.
There are other reasons that the test may be positive. Often miscarriage is incomplete and as long as there is placental tissue present, hCG will be produced, usually at a reduced rate. Some miscarriages do require a d7c to clean up the remnants. It is also possible to abort one twin and the other remains viable and healthy giving a positive reading.
A doctor is more interested in the rate of change of the hCG levels than in the mere presence of hCG. If the level is not increasing at a normal rate (and we do not really know what this is as it varies so much from woman to woman) other problems can be indicated including abnormal growths in the uterus or, at an extreme, ovarian cancer. The only medications that contain hCG are fertility drugs so this is not affected by other drugs, including birth control pills, that you may be taking.
OK, long response with no answer! That is because the home pregnancy tests are binary - yes or no - whilst bodies are analogue - the levels are ever changing. Best guess: if the miscarriage is complete, about a week later the hCG level should not register positive on a home pregnancy test.
The lingering feelings of pregnancy can be a function of the length of the pregnancy. After three weeks the body has not changed much but after nine weeks there wil be changes. The other part of it is psychological. A pregnancy scare stirs all sorts of strange feelings and many of them may become manifest through physical sensations or imagined sensations. Blood levels of hCG are much more telling than urine simply because the blood tests give an analogue result.
Waaaay back in my early twenties, I was three weeks late and then had the nastiest, most miserable period of my life. In retrospect, I certainly was pregnant and miscarried. The only symptom was the missed period. Following the miscarriage, I actually had breast tingles and some morning sickness - after clearly not being pregnant any more. I was also in denial that I had been pregnant and convinced myself that I had some malady that delayed the period. Post-miscarriage, my emotions ran both directions. And, I had no interest in sex until after the next normal period.
Thank god you are asking good questions and not just here wondering where your breasts go when you lie on your back! We have had a run of crap the last several weeks.
Brandye
Thank you for your answer. And I'm happy you consider these questions good :)
When I did the test, it was very confusing to see it was positive, even though I had felt 'strange' and like something was 'different' for about 10 days before. I decided I would cherish this unexpected gift! :) I kept it a secret for a few days, cause I couldn't find the right time to tell him. Than I started bleeding and cramping. I took another test just to make sure, which indicated neg. Tests were only 4 days apart (4 hell-of-days, cause my life flipped over twice!). If I understand your reply correctly; it seems possible the second test turned out negative even shortly after, because of the binary nature: HCG-levels could have been just above the first time and just below the second(?)
What happened after was mostly an emotional and mental struggle. Took me 2 weeks before I told my bf (who wished I had told him sooner, cause he knew something was up). Been in denial of my feelings for about 5 months (didn't dare to call it 'miscarriage', cause I thought it had been there too little time- had it been there? False positive? That would be a too 'big' word for something so small? No need to cry over something like that!) Until I finally allowed sadness and came to terms with myself with the help of -some anonymous- others :)
RedRoses
Your analysis is likely correct - slightly above the trigger level of the test to give you a positive and then fallen a bit below to give you the negative. Whilst false positive cannot be ruled out, as you describe the situation this is the best explanation.
You know, then, the power of the emotions causing physical manifestations. Quite typical. Some woman wanting to become pregnant will continue with symptoms, even missed periods, for most of what would have been their term if miscarriage had not occurred.
Dialogue such as this, Roses, will help others who may encounter this situation years into the future.
Brandye