The immortal philosopher and songwriter Tom Petty wrote this lyric “the waiting is the
hardest part”. Anybody who has been attempting pregnancy knows this is true. From the time of
ovulation if you are having intercourse or an embryo transfer if you are doing IVF,
the time it takes to determine whether you are pregnant can seem endless.
Why does it take so long? What does a pregnancy test measure anyway? Stay tuned and I will explain
Following fertilization of an egg, many embryos will start dividing. If the embryo is normal,
eventually, the cells will split into two groups,
cells that will become the fetus and cells that become the placenta and other tissues.
The cells that go on to form the placenta are called trophoblast cells. One of the
hormones that trophoblast cells make is called hCG. If an embryo implants into the uterus,
the trophoblast makes a connection with tiny blood vessels in the uterus called spiral
arteries. At that point, hCG can be detected by doing a blood test in the pregnant person.
It is not currently possible to detect a pregnancy before an embryo has implanted. How long does
it take for an embryo to implant? Back in 1999, scientists followed over 200 women for six months.
They tested them every day to determine the day of ovulation and for the earliest sign of pregnancy.
They found the earliest evidence for pregnancy implantation was 6 days after ovulation and the
latest was 12 days. 85% of implantations occurred 8 to 10 days after ovulation.
By the way, this study was done by testing hormones in the urine. hCG in the blood will
eventually be filtered by the kidneys and can then be detected in the urine.
hCG levels have to be higher to be detected in the urine compared to a blood test. It
therefore takes longer to identify a pregnancy using a urine test compared to a blood test.
Several factors can determine how soon after implantation a pregnancy can be detected. The
first, which I mentioned before, is whether you are doing a blood test or a urine test.
The second is the sensitivity of the test. Some tests are designed to be able to detect
lower levels of hCG and therefore can diagnose pregnancy earlier. The health of a pregnancy
can also impact the time of diagnosis of a pregnancy. If you subscribe to this channel,
you know that most embryos that humans make are not capable of producing a live birth. These
embryos may produce lower levels of hCG after implantation and therefore take longer to show
up on a pregnancy test. The presence of a multiple pregnancy can affect the timing also. For example,
a twin pregnancy may produce higher levels of hCG sooner and therefore allow for earlier
confirmation of a pregnancy.If you are doing a urine pregnancy test, then the ability to identify
hCG is going to be affected by how concentrated the urine is. If a person is very dehydrated,
the hCG in the urine will be more concentrated and a test may therefore pick it up sooner.
If you have been using fertility treatments,
it is important to be aware of whether you have taken medications that contain hCG. If you have,
then that could give you a positive result on a pregnancy test even though
you may not be pregnant. I talk about that more extensively in this video.
Our Infertility TV Bottom Line is this. The nature of human pregnancy is such that it
takes several days to determine whether a pregnancy has been established. The
earliest a pregnancy can be identified is roughly six day after ovulation.