A positive pregnancy test first happens about 3-4 days after implantation bleeding in a blood specimen and about 4-5 days before a missed period. The early urine home positive pregnancy test (HPT) is usually detected 6-7 days after implantation or as early as 2-3 days before the missed period. Implantation usually happens about 9 days (range 6-12 days) after ovulation, fertiliziation or about 8 days before the next period.
An early positive pregnancy test becomes positive only after the fertilized egg has arrived inside the uterus and implanted into the uterus and then sent enough amounts of hCG, human chorionic gonadotropin, the pregnancy hormone, into your blood stream and from there into the urine.
Positive Blood Pregnancy test
The blood pregnancy test is usually positive within 3-4 days after implantation or about 9-10 days after fertilization and ovulation. About 5-6 days before a missed period
Positive Urine early home Pregnancy Test (HOME HPT)
The early positive urine pregnancy test will become positive about 2-3 days after the positive blood test or about the time of a missed period, and sometimes a couple of days before the missed period. About 25% of pregnant women will test positive with the early home pregnancy test about 2 days before a missed period, and about 40% the day before the missed period.
The wide variation of when the urine pregnancy test becomes positive and how early pregnancy can be detected are due to four variables which determine when the home urine pregnancy test becomes positive:
A pregnancy test detects the presence of the pregnancy hormone hCG (human chorionic gonadotropin) either in the blood or in the urine only after implantation. Implantation can happen as early as six days and as late as 12 days after fertilization/ovulation. At the time of implantation the placenta starts making the pregnancy hormone hCG, which then enters the blood stream. How early pregnancy can be detected depends on the pregnancy hormone hcG which can be detected in the blood about three to four days after implantation. Urine hCG can be detected about two to three days after blood hCG can first be seen. Detection of hCG depends on timing of implantation, so hCG can normally be detected in the blood between nine and 16 days after ovulation (HPT: 12-19 days after ovulation).
There is a wide normal variation of hCG levels, both in the blood and the urine and this wide range changes the diagnosis of how early can pregnancy be detected. If a woman has a normal but low blood hCG levels, then it can take several more days for it to show up on a pregnancy test.
Urine hCG levels change over the course of the day depending on how much you drink and how diluted or concentrated the urine is. Urine pregnancy testing is best done with more concentrated urine. So how early can pregnancy be detected depends on the urine concentration and the quality of the early positive pregnancy test. If you drink a lot of fluid, the urine may be too diluted early on in pregnancy to achieve an hCG concentration adequate enough for a positive test.
Different pregnancy tests have different sensitivities and that has an impact on how early can pregnancy be detected. The lower the sensitivity, the earlier a pregnancy test becomes positive. Sensitivities are indicated in mIU/mL, the lowest amount of hCG in the urine that tests positive. A sensitivity of 20 mIU/mL requires one-half the hCG level to be positive when compared with a 40 mIU/mL sensitivity level, and it may become positive several days earlier than the pregnancy test with a higher sensitivity. Make sure you read the package of the pregnancy test to determine your pregnancy test's sensitivity.