Could someone please explain hCG levels to me?

[stilltired]

I have done so much research since I first thought I might be pregnant, I feel like I am back in health class in school, lol!

I've read a lot in many forums from women who insist that they kept getting negative hpts and negative blood tests until they were eight, nine, even 12 weeks pregnant.  But from the research I am doing, this does not seem humanly possible.

If a blood test, whether qualitative or quantitative, can detect levels of hcg above 5, how can a healthy pregnancy still not show up on a blood test until that far along, especially since a level below 5 is considered not pregnant?  I know these levels can vary greatly and that some women have low hCG levels and still deliver healthy beautiful babies, but by low does it mean lower than 5 all the way through the first trimester?!  I thought these levels reached their peak by weeks 8 to 11.  If it's still undetectable at 5, 6, 7, 8 weeks, etc, that would have to mean it was at 5, then spiked very quickly to its high point and then started going down again?

I'm just confused by how so many women have said that they got multiple negative tests (home tests and blood tests) and were still pregnant.  I would think it would be a rare and miraculous thing for a women to have undetectable levels of hCG in her bloodstream and actually be a few months pregnant, but there seem to be a lot of women who report this.  

The reason I'm questioning this is because I still haven't gotten a period even though I had a negative blood test and several negative hpts.  I know only the EXACT date of unprotected sex, and the blood test was negative 25 days after that.  Even if I didn't ovulate until 5 days after that (because sperm can live up to 5 days), the blood test was still 3 weeks after possible conception.  Since there's no chance I miscalculated the date of conception, if I had hCG levels that were still undetectable after 3 weeks (not just low, but actually undetectable), I would normally believe I'm not pregnant.  But people are telling me that I could still be pregnant because I haven't gotten my period still, and even though I'm still inclined to think I'm not pregnant I am worried that on the off chance I am and my hCG is still undetectable then something could be wrong.

[cminamyer]

Once implantation occurs it starts to produce hcg.  Also, the hcg levels have to double every 48 to 72 hours...so, they can start off at 5, but by two days later they should be 10, two days later 20, then 40 and so on. so at 8 days after implantation, you should have a detectable amount of HCG. I am not saying it cannot happen, but in my opinion the women who say they have a negative home pregnancy test until 12 weeks probably mis-calculated their date. your levels should level out after the first trimester, but if hey drop during the first couple of weeks, then it may be an indication of a miscarrige. I would venture to guess that your not pregnant this time, maybe next time. Good Luck.

[JoyRenee]

I honestly don't believe posts like that, unless there was a lab error with the blood tests. I just don't see how they'd get negatives either as your levels get VERY high in early pregnancy. So I don't know what to tell you except to trust the tests. Leave some room for error but after some time you just have to know that a negative probably means negative.

[bryanarae]

When I was pregnant with my son, every hpt I took up unitl 11 1/2 weeks would show negative. After 2 months of not getting a period I decided to go to the doctors. I waited that long because I knew it was normal to miss a period every once in a while. But when it didn't show up the foloowing month I went to see my doctor. He gave me a urine pregnancy test and it also came out negative. He asked me to come back in a couple of weeks in my period never came about. 2 1/2 weeks later I went back to my doctors office and finally got a very faint positive, went for blood work and showed a positive pregnancy. I was then booked for my first ultrasound to find I was 12 1/2 weeks pregnant. I had taken multiple brands of hpts during the couple months and they always would show negative. But as soon as I went for blood work, my hcg levels were really high.
Why I never got a positive hpt we don't know. Was it weird? Yes. But as for those ladies that say they never got a positive even with blood work until that far along is weird. But hpts I guess I can understand. But this time around I got a positive hpt and 4 weeks and 2 days. So I have no idea why it worked this time and not last.

[stilltired]

Thanks for sharing your insights.  I know every women is different, but I'm trying to determine how anyone could still have hCG levels less than 5 by 3 or 4 weeks after fertilization.  I can see having low levels, say 10 or 20 by then, but less than 5, how could that be?  Doesn't the body need hCG to help keep the baby?  

Is there anybody out there who still got a negative blood test 2 weeks or more after implantation?  I don't see how the body could have not produced enough hCG by then to be detected.  

And what's the latest time implantation could occur?  I know it's usually within 6 to 12 days after, but can it be a lot longer?  It wouldn't seem possible to have implantation occur a full 2 or 3 weeks after fertilization.  And if the body starts producing hCG once implantation occurs and the baby is connected to your bloodstream, how can anyone ever have hCG less than 5 after maybe a week after implantation?  Even if you miscalculate the conception date or the date of your last period it still stands to reason that by weeks into a healthy pregnancy a qualitative blood test would get a hit on hCG.  

If I were pregnant and based it on the possible conception date I'd be 3 1/2 weeks pregnant when the blood test was done (and if I based it on my lmp I'd have been 6 1/2 weeks.) I know I keep saying this, but based on the day I think I had implantation bleeding, the test was 13 full days after that, so if I didn't have detectable levels of hCG in my blood by then I should consider myself not pregnant.  But then I read a post somewhere from a woman who claims her hCG level was 2 when she was tested 3 weeks after fertilization.  That doesn't sound possible!

[nevaeh222]

I had my blood test at 11 days past my IUI. My HCG level was only 4. 2 days later it was 12. I got a level of 4 at 3.5 weeks. You should be seeing some kind of rise in the HCG if you are indeed pregnant. I still haven't gotten a positive on an hpt though.

[stilltired]

Thanks for your response!  What is IUI?