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Fertility blood tests and why timing is important – don’t always listen to your doctor

In this article we are going to look specifically at the progesterone fertility blood test as part of your fertility workup. We will consider what progesterone is, why it’s important and when the best time to have the blood test is.

Fertility testing – Fertility blood Tests

If you have been trying to get pregnant for a while and have had no luck, when you go to your G.P. or physician it is likely they will refer you to a fertility clinic or Gynaecologist who will start some initial fertility testing (for more information on the fertility tests you might have check out our fertility testing guide). As part of a fertility workup you will be asked to attend the phlebotomist or nurse’s clinic for some blood tests to check your hormone levels at certain points in your menstrual cycle.

These will likely include but are not restricted to: Follicular stimulating hormone, luteinising hormone, oestradiol (the main type of biologically oestrogen) and progesterone initially. These first 3 tests are most likely to be done around days 2-4 of your cycles (day 1 of your cycle is the first day of your period) although your doctor will tell you exactly when to have them done. Progesterone, however, is a little trickier.

For almost every part of your journey I will always say to listen to your doctor and follow their advice. The timing of the progesterone test, however, is the exception to my rule. Now, don’t misunderstand me, most specialist doctors and nurses will advise you correctly, the advice they give is based on the idea that a women doesn’t know exactly when she ovulates so they have to find a simpler method of trying to time the test.

But why do you need the test? Let’s look at why the progesterone test is important.

Timing the progesterone fertility blood test is vital

Why is progesterone important?

Progesterone is the hormone that during the menstrual cycle prepares your uterus for the implantation of an embryo and therefore is at it’s highest in the luteal phase of yours cycle (the final stage – after ovulation and before your period). For more information have a look at our guide to a women’s menstrual cycle. A fertility blood test measuring progesterone levels are therefore used to confirm that you have ovulated as they will rise after ovulation has occurred. As you can imagine this is a very important test as if this test comes back negative your doctor will believe you do not ovulate. If you are not ovulating you can’t get pregnant.

The medical advice and where it comes from…

Now a lot of medical advice is based around the idea that a women has a beautiful regular 28 day cycle which is made up of a 13 day follicular phase (the beginning of your period until ovulation), you then ovulate on day 14 of your cycle and the final 14 days are your luteal phase (ovulation to your next period). While this is a lovely and neat ideal, it is not reality for most of us. Doctors want to catch your progesterone levels at an optimal time during your luteal phase and believe that about halfway through is the best time, so 7 days before your period is the ideal. This is probably fantastic for most women. However, for those with longer or shorter cycles where our luteal phase is shorter than 14 days this may not work out quite as perfectly. A normal luteal phase is 10-17 days long

My progesterone fertility blood test story

I had been tracking my menstrual cycle since before I was trying to conceive (TTC), my cycles were regular but varied from a 24-34 days in length which meant a possible 10 days when my period could turn up. Most of us would agree this is less than convenient. So, to take back some control and not be caught unawares I began tracking my basal body temperature so I could pinpoint ovulation each cycle. After doing some reading on cycle tracking, I knew that a women’s luteal phase tended to be same length each month with usually only a variation of a day either side. After a few months of working out where I ovulated, I could see that my luteal phase was most commonly 11 days long. This allowed me pre-TTC to track my cycle each month, confirm ovulation and then count 10 days ahead and know that my period would likely come in the next 2-3 days. Hurrah! For more information on how to track ovulation then check out our ovulation tracking article.

So when it then came to TTC I knew I ovulated, and I knew that Nathan and I were managing to baby dance (have sex) during my fertile period to catch ovulation each month and felt sure it wouldn’t take us too long to get pregnant. So, when, 15 months later we sought medical help and were sent to a fertility specialist for testing I knew that I ovulated each month. However, I needed to prove to the doctors this was the case with my progesterone test.

The nurse in the clinic gave me the standard advice of getting the progesterone blood test done – 7 days before my period. Not a problem for most women, however, with only having a 11-day luteal phase I knew that would only put me at 4 days post ovulation (4DPO). My hormone levels at this point would not be high enough to confirm I had ovulated. The doctors are looking for hormone levels they would see in a woman who was a week post ovulation and they would be too low as I wouldn’t far enough into my luteal phase.

Having spoken to a different fertility specialist nurse previously, I knew the levels should be taken 7 days after I ovulated, so luckily, I did this instead and everything came back in range showing that I do ovulate. However, if you were unaware and did the test too early or too late you could end up being misdiagnosed and even on medication you don’t need.

The big problem being most women don’t know when they ovulate so the clinics can’t ask the women to do the test 7 days after ovulation as they may not know when that is. Therefore, they ask for levels to be tested 7 days before your period, but this is not helpful if you have irregular cycles, a a little bit of variation in your cycle length or a shorter luteal phase (please note you need a luteal phase of at least 10 days for an embryo to implant so if your is shorter you should seek medical advice). Let’s face it, for some women knowing when 7 days before their period due is a challenge in itself.

My advice for timing the fertility blood test

My advice is simple and complex at the same time… track your ovulation! Now ovulation tracking can be quite daunting (if you’re interested in ovulation tracking check our article on how to track ovulation). However, I am really an advocate of understanding your own body and how it works and ovulation tracking can help you understand when you are most fertile, when you ovulate and whether there are any concerns such as not ovulating, ovulating irregularly or a short luteal phase before you head to the doctor. It also then allows you to time your progesterone fertility blood test properly – 7 days after you ovulate.

If you have any questions, want any advice or simply want to share you story of the timing of you progesterone blood test then please comment down below or get in touch at info@ineedivf.co.uk.


not timing the fertility blood test could mean you have to take medication you don't need
Get your progesterone fertility blood test done 7 days after ovulation

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Where next?

Menstrual Cycles – If you’ve found this interesting but are still unsure on the role of progesterone in your menstrual cycle or just want a better understanding then head to our article on menstrual cycles.

Ovulation Tracking – Feeling inspired and want to start tracking your ovulation or just want to find out a little more about how it works then this is the article for you.

Fertility Tests – Want to know more about what to expect in terms of initial fertility testing then check our guide to initial fertility tests.

The timing of some fertility blood tests is absolutely vital and due to minimal general doctor training in fertility this can often mean they give you the wrong advice.
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