Fertility Blood Test Day 21

What Is The Day 21 Fertility Blood Test?

The Day 21 fertility blood test is simply a blood draw that is done in order to determine the amount of progesterone present in a woman’s blood sample, approximately one week after ovulation is expected to have occurred. The test is one of the easiest ways to confirm ovulation with a blood test, as opposed to using ovulation predictor tests or basal body temperature.

While the number varies from person to person, a standard menstrual cycle is considered to be 28 days long, hence the name "21 Day”. That said, the timing of the progesterone test must be adjusted to the individual’s cycle length.

Why Progesterone Is The Key Hormone Here

Since the Day 21 test measures progesterone levels, it is important to first understand the hormone's role in the female body.

Following ovulation, the follicle from which the egg was released develops into a corpus luteum, which starts secreting progesterone, a hormone with the main function of preparing the uterine lining (the endometrium) for a possible fertilised egg. If the amount of progesterone secreted by the corpus luteum is insufficient, the uterine lining may be less receptive for the fertilised egg.

It is important to know that progesterone is released in meaningful quantities in the body only after ovulation. This means that high progesterone levels found in the test indicate that ovulation has successfully occurred. This is the scientific basis for confirming ovulation with a blood test.

When progesterone concentrations are low or absent, this may indicate that ovulation did not occur during that menstrual cycle, a condition known as anovulation. It may also indicate that the corpus luteum is not functioning optimally.

When To Take The Day 21 Fertility Blood Test

As mentioned above, cycle lengths may vary among women, which is why the timing of the progesterone test should be personalised. The best time to take the test is about seven days before the next expected period.

What Do The Results Mean?

Progesterone levels are usually measured in nanomoles per litre in countries that use the SI system. Thus, the results generally indicate the following:

• Below 3 nmol/L: The interpretation here would be that ovulation had not happened during the menstrual cycle. However, please note that a single result of this kind cannot determine the presence of a long-term problem. Further testing is recommended, especially if results are repeated across several cycles.
• 3 to 16 nmol/L: Such results are ambiguous. In other words, ovulation might or might not have occurred. Either way, the test might have been timed inappropriately, or the corpus luteum might be secreting insufficient progesterone.
• Above 16 nmol/L: This generally means that ovulation did take place in the cycle.

It is advised that individuals should take the progesterone test across multiple cycles, as isolated interpretations should be avoided.

What Happens After Your Results

Once your results for the progesterone test are in, your doctor will go over them along with your complete medical history. Should your ovulation seem to be fine, then other causes will need to be explored. In case the results indicate problems with anovulation or a hormonal imbalance, then more tests will usually be performed before proceeding.

Your Day 21 blood test should be a starting point instead of a final verdict. Some women find themselves testing low once and testing fine another time. There are many stressors that can cause ovulation to be compromised, such as sickness, dramatic weight fluctuations, and disrupted sleeping patterns.

Conclusion

The Day 21 progesterone test is considered one of the most reliable ways to confirm ovulation with a blood test. This test will provide your doctor with the necessary information regarding whether there is enough hormonal activity in your body for possible conception. The key to obtaining accurate results for this examination is taking the test 7 days before your period rather than on Day 21 of your cycle.