There
is a lot of confusion an ambiguity about blood pregnancy tests.
Although they are very precise and more sensitive than urine
tests, they still require one thing - HCG to be present in
the women's blood stream. Blood tests can detect very low
levels of HCG and can confirm pregnancy with as little as
5 mIU/ml in the blood. (Although most tests are looking for
a number 25 mIU/ml or higher.)
Implantation
and HCG levels
HCG is
produced at least in small quantities from the moment of conception,
so why can't you get a positive result on a pregnancy test
right away? In order to get a positive pregnancy test, blood
or urine, HCG has to be present in the woman's blood stream.
Once the egg implants it burrows into the woman's uterus connecting
the baby directly to the woman's blood stream. Until implantation
occurs, your developing baby, the fertilized egg is not directly
connected to your blood stream. Only when implantation occurs
will their be enough HCG present in your blood stream to confirm
pregnancy.
Implantation
time varies, averaging between 6 to 12 days past ovulation.
If your baby implanted late in your cycle and your test was
performed early, you could get a negative test result on a
pregnancy test when you actually are pregnant.
Miscalculating
your period
Another
reason you might get a negative pregnancy test is miscalculating
when your period is due and/or when ovulation occurred. If
you miscalculated your ovulation date by even a few days,
you could be testing too early and get a negative test result.
If you
think you are pregnant and received negative pregnancy test
results, the best thing to do is wait a week and retest either
with a home pregnancy test or a follow up blood test.