[VIDEO] So, you’re trying to get pregnant and you’ve been to see your doctor to get some basic fertility testing done. And your doctor has ordered something called a Day 21 progesterone test (otherwise known as a serum progesterone test or progesterone blood test).
This Day 21 progesterone test is one of the easiest ways to find out if you’re ovulating or not.
But as you might have heard, the test is NOT foolproof. If it’s not done correctly, you could be told that you’re not ovulating, even when you are. Not something you want to hear when you’re trying to get pregnant!
So, in this article, I’m going to explain how to do your Day 21 progesterone test the RIGHT way to make sure you get a reliable result – and to find out for SURE if you’re ovulating or not.
Before I dive in, let’s look at why you’d have this test done in the first place.
What’s the Day 21 progesterone blood test for?
The Day 21 progesterone test is one of the first fertility tests your doctor’s likely to order if you’re having difficulty getting pregnant. It’s sometimes also ordered in advance of trying to conceive, as part of a preconception checkup.
Normally, your doctor will test some of your other hormone levels at the same time. This typically includes follicle stimulating hormone (FSH), estradiol and perhaps antimullerian (AMH) and thyroid hormones (TSH and T4) also.
The Day 21 progesterone test is used specifically to find out if you’re ovulating or not and perhaps to also check if your progesterone levels are high enough for successful implantation.
The problem with the Day 21 progesterone test
Now don’t get me wrong, I am a fan of the progesterone blood test. It can be very useful. But the test comes with a HUGE caveat.
You’ll only get a reliable result if your blood is drawn on the RIGHT day of your menstrual cycle. If it’s not done on the right day of your cycle, you can get a result that’s inconclusive. Or even worse, as I mentioned earlier, a result that suggests you’re not ovulating, even when you are.
Now you might be thinking that surely it’s obvious what day of your cycle you should get the test done – Day 21 right? After all, it is often called the Day 21 blood test!
But the truth is, there’s a very good chance this will NOT actually be the correct day for you. And that doing the test on Day 21 of your cycle could actually give you an unreliable result – and potentially, cause you a whole lot of unnecessary worry.
Let me explain.
Why testing on Day 21 could be the WRONG day for you
If you’ve read my other article on the progesterone blood test, you’ll know that before ovulation, your progesterone levels are very low. Then after ovulation they increase dramatically. Your progesterone levels reach their peak around 7 days after ovulation.
It’s this PEAK in progesterone, that we want to measure.
The problem is, most women don’t know EXACTLY when they’ve ovulated. This means they don’t know when 7 days after ovulation is. And if you’ve read some of my other articles, you’ll know that most fertility apps (and sometimes, even ovulation predictor kits) aren’t a reliable indicator of the day you’ve ovulated.
So, because of this, the progesterone blood test is often ordered for Day 21 of your cycle – on the assumption that you’ve ovulated around Day 14:
Day 14 ovulation + 7 days to reach peak progesterone = Day 21.
But this is a BIG assumption. Because as a number of scientific studies have proven, and as I see with my clients all the time, most women do NOT ovulate on the ‘textbook’ Day 14.
So, getting the test done on Day 21 of your cycle may NOT be the right day for you. The right day for you, will depend entirely on when YOU ovulate in that particular cycle.
When to do the progesterone blood test – a couple of examples
So let’s take a look at a couple of examples to show you what I mean.
If you ovulate early, for example on Day 10 of your cycle, you’d want to do the test around Day 17 – 7 days after ovulation.
Day 10 ovulation + 7 days to reach peak progesterone = Day 17
If you wait until Day 21, that’s going to be too late. By Day 21, your progesterone levels will be on their way back down or quite low again and you’ll have missed the peak that we want to measure.
At the other end of the scale, if you ovulate late, on Day 23 for example, you’d want to do the progesterone test around Day 30, again, 7 days after ovulation.
Day 23 ovulation + 7 days to reach peak progesterone = Day 3
A Day 21 test would be much too early. On Day 21, you wouldn’t have ovulated yet, so your progesterone levels would still be low.
In both these cases, these lower progesterone levels could make the test inconclusive or even suggest that you’re not ovulating, even when you are.
How to get a reliable result
So, what SHOULD you do, to make sure you get a reliable result?
If you’ve got regular cycles, one thing you can do is to work out when your next period is due and subtract 7 days from that due date. Try to get your blood drawn on this date, or as close to it as possible.
Your doctor may have suggested this to you already. This method will often give you the correct timing, but NOT always – especially if you have irregular cycles. The length of your individual luteal phase will also impact on whether this timing works for you.
An even better thing to do, especially if you don’t have regular cycles, is to chart your fertility.
In my opinion, charting your fertility (monitoring and recording your basal body temperature and cervical fluid) is by far the best method to figure out exactly when you’re ovulating.
It’s an easy, reliable method that you can use at home and in my Fast Track to Pregnancy Program I show you exactly how to chart your fertility, step by step.
Ironically though, if you do chart your fertility, you won’t actually NEED to do a progesterone blood test. Your fertility charts themselves will have already told you whether you’re ovulating or not. But it can still be helpful to have the blood test as a backup.
Once you get the result of your progesterone blood test, your doctor will be able to explain to you what it means. But if this hasn’t happened, or if you still need further clarification, this article helps explain what YOUR progesterone level means for ovulation and for your chances of getting pregnant.
Take home message
The Day 21 progesterone blood test can be a useful and easy test to find out if you’re ovulating or not. But to get a reliable result, your blood MUST be drawn around 7 days after ovulation.
To figure out the day that you’re ovulating (and to gain loads of other valuable information about your fertility and reproductive health ), I highly recommend learning to chart your fertility.