Not all women have a positive urine pregnancy test exactly on the same day of their cycle. While a blood pregnancy test is usually positive about 8-10 days after fertilization and ovulation, there is a wider range of timing of when the urine pregnancy test becomes positive.
are four major variables that determine when the urine pregnancy test becomes positive:
- Timing of Implantation
- Blood hCG level
- Urine hCG level
- Sensitivity of the pregnancy test
1. Timing of Implantation A pregnancy test detects the presence of the pregnancy hormone hCG (human chorionic gonadotropin) either in the blood or in the urine. The hCG in the urine comes from the hCG in the blood after it was filtered through the kidney. After ovulation, the egg gets fertilized and travels through the fallopian tube toward the uterus. This travel takes on average about a week. Implantation, the attachment of the fertilized egg in the lining of the uterus, occurs on average eight to 10 days after ovulation/fertilization, but it 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. hCG 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).
2. Blood hCG Level There is a wide normal variation of hCG levels, both in the blood and the urine. If a woman has low hCG levels, for example, then it can take several more days for it to show up on a pregnancy test.
3. Urine hCG Level 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. 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.
4. Sensitivity of Pregnancy Test Different pregnancy tests have different sensitivities. 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.