If you’re using hormonal contraception and thinking about checking your hormones, you’re not alone. One of the most common questions women ask is: “Should I still test on Day 21?” And the honest answer is: it depends on the type of contraception you’re using.

Hormonal contraception can completely change the way your natural cycle behaves, which means the usual rules about when to test don’t always apply. Let’s break it down in a simple, no-nonsense way.

Why “Day 21” Doesn’t Work for Everyone

The classic Day-21 blood test only makes sense if you ovulate regularly and have a roughly 28-day cycle. It’s designed to capture a progesterone peak after ovulation.

But if your contraception is stopping ovulation, or making your cycle irregular, then Day 21 becomes a meaningless number. The good news is that we can still get useful information—we just need to understand what your contraception is doing in the background.

1. The Combined Pill

The combined pill contains synthetic oestrogen and progestogen, and its job is to switch off ovulation completely.

That means:

• you don’t get a normal cycle
• FSH, LH, and natural oestradiol stay low
• your “bleed” isn’t a real period, just a withdrawal bleed

What this means for hormone testing If you take the combined pill, FSH, LH, oestradiol and progesterone won’t tell us much about your natural hormones—they’re all suppressed by design. Day-21 testing doesn’t apply because there’s no ovulation to measure.

You can still test helpful things like thyroid function, prolactin, testosterone and other general health markers, but natural ovarian hormones won’t show their true pattern until you’re off the pill for a little while.

2. The Progestogen-Only Pill (Mini Pill)

The mini pill is a bit more unpredictable. Some women still ovulate, some don’t, and some ovulate only occasionally.

How it affects hormone tests

Because ovulation is hit-and-miss:

• progesterone won’t reliably rise mid-cycle
• FSH, LH and oestradiol may look normal… or not
• Day-21 testing isn’t meaningful

You can still test other hormones that aren’t tied to ovulation, but cycle-based hormones become harder to interpret.

3. The Hormonal IUD (Mirena, Kyleena)

The hormonal IUD releases levonorgestrel mainly inside the uterus. It can affect periods, but it doesn’t consistently shut down ovulation. Many women continue to ovulate normally.

What this means for testing

This is where things get easier.

• FSH, LH and oestradiol are still useful
• Progesterone may or may not peak depending on whether you ovulated that month
• You don’t need to test on Day 21
• Any-day testing is usually fine unless instructed otherwise

Even though your bleeding pattern might not look “normal,” your ovaries are often still doing their thing behind the scenes.

4. Copper IUD

This one is simple. The copper coil contains no hormones, so it doesn’t interfere with your natural cycle at all.

Testing is straightforward

• FSH, LH, oestradiol and progesterone all behave normally
• Day-21 progesterone is meaningful if your cycle is regular
• You can interpret blood tests the same way you would without contraception

So When Is Blood Hormone Testing Helpful?

No matter which contraception you’re using, blood tests can still give valuable insights into:

• thyroid function
• prolactin
• testosterone and other androgens
• metabolic health
• ovarian reserve (AMH)

What changes is how well we can interpret your cycle hormones (oestradiol, progesterone, FSH, LH). If your contraception suppresses ovulation, those markers simply won’t reflect your natural rhythm.

Bringing It All Together

Hormonal contraception doesn’t stop you from testing your hormones, but it does change what we can learn from the results.

Combined pill: Natural hormones suppressed → cycle tests not useful

Mini pill: Ovulation inconsistent → cycle tests unreliable

Hormonal IUD: Ovulation often continues → many cycle markers still useful

Copper IUD: No hormonal effect → all cycle tests interpretable, including Day-21 progesterone

Find out more with i-screen's Hormone Imbalance Test.