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Fertility Cycle Monitoring: Day 3 and Day 21 Tests

Fertility Cycle Monitoring
If you have been preparing for infertility treatment, it is important to understand how cycle monitoring works, specifically for Day 3 and Day 21. This allows your fertility specialist to track hormone levels, the size of the follicles, and the lining of the uterus in terms of its thickness.

We will look at the steps taken for Day 3 and Day 21 testing and how the results affect the chances of fertilization.

What to Expect on Day 3 of Cycle Monitoring?

When beginning treatment, you will likely get a blood test on the third day of your menstruation cycle (which is your third day of menstruation) so that your doctor can access your levels of Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), and Estradiol (E2).

Hormone tests done on Day 3 of cycle monitoring are used along with results from an ultrasound and a physical to help establish your fertility stage. Your medical history is also considered. The timing of this test gauges the quality and quantity of the eggs and the functioning capability of the ovaries.

The FSH Blood Test

As FSH promotes egg and estrogen production in the early days of the menstrual cycle, a FSH blood test is done to measure a women’s fertility status. At this time, the FHS levels are low. As these levels increase, the eggs mature.

It’s important to measure the FSH level on Day 3 of cycle monitoring because high levels could indicate low egg reserve. Each testing laboratory has its own set of range levels for comparison. The woman’s age is also used as a measurement as levels vary as one ages.

For men, the FSH blood test is used to measure sperm count as this hormone is responsible for sperm production and movement.

The LH Blood Test

LH levels are important for cycle monitoring as this hormone dictates the span of the menstruation cycle as well as stimulates ovulation. While the LH level is low at the beginning of the cycle, it quickly increases prior to ovulation, usually within 24 to 36 hours.

Extremely high or low levels at Day 3 may indicate irregularities. For the male, this hormone promotes creation of testosterone, which is necessary for sperm production.


Estradiol, or E2, helps to control the reproductive system by stimulating the release of the eggs and promoting the thickness of the uterus lining. Estrogen controls the production levels of FSH in the brain.

Estradiol levels for Day 3 testing are compared with the FSH level findings. This is to ensure a normal FSH reading is accurate and to see whether the eggs are of a lower quality and quantity.

Estradiol also plays an important role in sperm cell production.

Also Read: Cycle Monitoring: What to Expect, the Benefits, and the Limitations

What Do Day 3 Tests Show?

Day 3 cycle monitoring is important in the infertility treatment because of the implications of the FSH, LH, and E2 levels. Known as the “baseline”, Day 3 allows an accurate reading of these hormones before levels increase.

As laboratory clinics follow their own set of measurements, Day 3 testing are assessed on a reference range. Every woman and man have variable factors in relation to fertility markers. These tests allow for categories of low, normal, and high.

Day 3 hormone testing compares specific reference ranges within this follicular phase of the menstruation cycle. Results are used to detect any irregular indicators within your reproductive system.

What Are the Normal Results for Day 3 Cycle Monitoring?

There are many variables with Day 3 cycle monitoring including age, medical history, and fertility stage. For the most part, the normal ranges indicate potential for a successful fertilization.

The FHS is measured in milli-international units per millilitre (mIU/ml). Women with FSH levels measuring lower than 15 mIU/ml have been shown to have an increased rate of pregnancy success.

Clinical LH blood tests measure the amount in international units per litre (IU/L). For those with regular periods, a normal range of LH levels measure between 1.9-14.6 IU/L is expected at this time.

From this, what is considered normal Estradiol levels on Day 3 cycle monitoring is generally measured at 50 pg/ml (picograms per millilitre). In clinical terms, 1 picogram is one-trillionth of a gram.

What Is Day 21 of Cycle Monitoring?

Day 21 of cycle monitoring is another critical milestone for fertility testing procedures. At this time, the focus is on the progesterone levels, with a checkup of other hormones.

A regular menstrual cycle is around 28 days with the 14th day being the time of ovulation. Testing for progesterone establishes whether the woman has ovulated and is in the second half of the menstrual cycle, known as the luteal phase.

What happens on Day 21 of cycle monitoring? This involves testing the progesterone levels. It is usually at this time the Estradiol level is retested to ensure levels have peaked.


Progesterone is a natural hormone vital to thicken the uterine lining as it prepares the uterus for a pregnancy. In men, this same hormone assists in the development of sperm.

Testing the progesterone levels provides insight as to whether ovulation has occurred, hence an environment for a potential implantation. Theses levels are projected to peak around the 21-day mark.

What Are Normal Results for Day 21

Low progesterone levels at Day 21 suggest no egg has been produced, eliminating the chance of pregnancy that month. Ideal levels register at 10 ng/ml, (nanograms per millilitre).

Learn More about ONE Fertility Kitchener Waterloo’s Cycle Monitoring Service

For the most comprehensive fertility care, choose the personal care and treatment at ONE Fertility Kitchener Waterloo. Using evidence-based care, our knowledgeable and certified team can help you design a plan customized to your needs and comfort. Contact us today to book a consultation with one of our esteemed fertility specialists.


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