Fertile Window


Fertile Windowhow to maximize your chance at conception each month

The menstrual cycle consists of an ebb and flow of specific hormones produced by the pituitary gland (in the brain) and the ovaries. The key players from the pituitary gland are Follicle Simulating Hormone (FSH) and Luteinizing Hormone (LH), and from the ovaries are estrogen and progesterone.

At the start of your cycle (day 1 of your period), the pituitary produces FSH to stimulate the ovaries to produce follicles for the cycle. FSH is also going to stimulate your ovaries to produce estrogen. Estrogen is needed to build a healthy uterine lining to optimize egg implantation when fertilization happens. As estrogen levels begin to climb, it will suppress FSH secretion from the pituitary gland, and stimulate LH secretion from the pituitary gland. This LH surge typically occurs ~14 days prior to your next expected period.

Example: if you have a 28-day cycle, your LH surge/ovulation typically occurs around day 14, if you have a 32-day cycle, your LH surge/ ovulation typically occurs around day 18.


The LH “surge” from the pituitary gland will signal to the dominant follicle that has been developing in your ovaries to release the egg from the follicle (ovulation). The Egg is moved from the ovary into your fallopian tube where hopefully sperm is already waiting or will be arriving there shortly to fertilize your egg! The fertilized egg (now called a blastocyst) travels down the fallopian tube to the uterus to then implant and grow into your baby. The remainder of the events to come after implantation is a story for another time.

Here’s an awesome graphic that shows the interplay of the hormones I’ve been talking about:

Screen Shot 2018-11-27 at 10.38.54 AM

Now that you know the key hormones involved in making ovulation happen, I’d like to speak more specifically to the “Fertile Window”.

Sperm can swim around in your uterus and fallopian tubes all it likes for maximum 5-6 days then it will degrade. If there’s no egg in sight to fertilize, no baby will be made.  Similar to sperm, your egg will also break down and degrade 24-36 hours after ovulation if it does not get fertilized. So ideally you want fresh sperm in your fallopian tubes ready and waiting for when ovulation happens. Keeping in mind, the longer the sperm is sitting in there it will slowly be degrading, becoming less optimal and healthy. You want intercourse to happen a day or so before ovulation to better your chances at a positive pregnancy test!

This is a fantastic graphic that depicts your fertile window:

Screen Shot 2018-11-27 at 11.01.15 AM

What are some signs I can look for to know I’m in my Fertile Window?

  1. First and foremost, get familiar with your cycle!

Become acquainted with the length of your cycle, any changes that may be happening to your body during your cycle and when you feel those changes (breast changes, mood changes, food cravings, cramps, energy levels) and keep track of those signs and symptoms. Even if babies are in the distant future for you and your partner, the more familiar you get with your cycle now, the easier it’ll be when the time comes to conceive because you’re already familiar with the signs your body makes throughout your cycle and when you are ovulating.

There are some helpful phone apps available you can use to keep track of your cycle length, signs and symptoms, intercourse frequency and much more! I’d recommend:

  • Ovia Fertility
  • Kindara
  • Clue
  • Monthly Cycles
  • Nature Cycles
    • There are many more out there, find one that is easy for you to use, and makes sense to you!
  1. Track your Basal Body Temperature (BBT)

First thing each morning roughly around the same time (before you’ve had your morning coffee or brushed your teeth!) take your temperature (with a thermometer that has 2 decimal places for the best precision). When you ovulate, your ovaries begin to produce progesterone, which will raise your BBT slightly. If you’re keeping track on a chart, you will see an obvious spike in your temperature for the second half of your cycle if ovulation occurs.

With respect to planning intercourse around your fertile window, the morning you see your temperature spike significantly on your tracking chart around mid-cycle means ovulation has happened and is a good indication to get busy and make that baby because you’re potentially on the last day of your fertile window this month!

Tracking your BBT is a great tool to use month to month, allowing you get to know your cycle and you can then begin to predict what day ovulation is going to occur to best time intercourse the day before your expected spike in temperature, so the sperm will be there ready and waiting for when the egg is released.

Here is an example of what tracking your BBT will look like – also note if your hormones are imbalanced or you aren’t ovulating, a BBT is a good glimpse into your hormone health and can indicate if further work up (labs) and treatment (diet, herbs, supplements) are required to get your hormones back in balance! The phone apps listed above also have options to track your BBT within the app too.

BBT example

3. Cervical mucous

The human body is ingenious! When you are approaching ovulation, the mucous produced around your cervix changes its composition and consistency to better transport and nourish sperm so the sperm can last longer and make it to the egg. Fertile cervical mucous is best described as a “raw egg white” consistency. Your body will make fertile cervical mucous a couple days leading up to ovulation, so pay some attention when you’re going to the bathroom when you think you’re gearing up for ovulation and look for clear “egg white” discharge. Or if you’re super curious use your fingers to collect some of the mucous and examine it. It will be a clear fluid that is thin and stretchy!

4. Increased Libido

Another fantastic baby making feature built into our biochemistry. With the rise in estrogen leading up to the LH surge, testosterone also rises with it, and together those hormones increase sex drive. If you’re feeling particularly attracted to your partner around the middle of your cycle, it may be your body telling you you’re gearing up for ovulation!

5. Mittelschmerz

I promise I didn’t just make that word up. That’s the term used to describe the lower abdominal cramping that may be experienced while ovulating. It may be a gentle sensation you may not think twice about, or it may be a significant cramp that lingers on the one side. Either way, it is a physical sign you can look for to alert you that ovulation is occurring.

These 5 points listed above are all subtle changes your body has leading up to ovulation. Each point on their own may not be enough to confidently target when you are ovulating, but if you get to know your cycle, and keep track of all these little details your body is trying to tell you and compile the information, you have a significantly better chance at timing intercourse on your fertile window which increases your chances of conception!

Happy baby-making,

Dr. Lewis

Information in this post is intended as general information. It is not to replace medical advice from your primary care physician.

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