Sex: timing is everything in the dance of creating life 

By Repromed Scientific Director, Dr Debbie Blake

They say timing is everything, and never has that been more true than for the incredible union of eggs and sperm. Dr Debbie Blake explains how your body prepares itself every month, with a small window of time to receive sperm. Understanding this fascinating process and tracking your ovulation are important steps in starting your fertility journey.

The dance of egg and sperm

Once you gain an understanding and appreciation for the carefully choreographed dance of these two cell types to create life, it is hard not to be amazed at the cleverness of nature and wonderment that they get their rhythm so perfect, so often.

Release of the egg from the ovary is the result of a finely orchestrated cascade of events that starts with the two controlling glands in the brain called the pituitary and hypothalamus, who themselves are controlled by our internal and external environment.

Over the course of 12 days or so, these glands send signals in the form of Follicle Stimulating Hormones (FSH), to the ovaries to kickstart the maturation process of the egg, which in turn releases hormones that cultivate the lining of the uterus to thicken with blood supply.

An intricate feedback system from the ovary to the hypothalamus then signals that the time is right to prepare for the next act, which is to modify the chemical structure of the cervical mucus. This sets the scene for receiving the sperm.

When the egg and uterine lining is still busy growing and maturing, the cervical mucus acts like a locked door. It is white in appearance with a thick consistency, because the chemical structure is a crossed lattice – work of molecules, making it impenetrable to sperm. 

But in the two to three days leading up to ovulation of the egg, the mucus changes its chemistry under the influence of oestrogen. Now the mucus molecules become long and linear, with a clear egg-white appearance and stretchy consistency, finally allowing sperm to not only enter, but thrive.

This crucially lasts only for around a critical 10 hours in a whole month. Then when the optimal time has passed, the cervical door shuts again and the mucus loses its clear and glossy properties again.

Tracking your ovulation

I had a degree in reproductive biology and several years of experience as an IVF Embryologist before I was first exposed to the concept that it was possible to develop an awareness of your natural bodily functions to predict and sometimes feel, when you were about to ovulate. I wondered – why was I not taught this, by my mum or even school?

(It only came about, when I had invited one of the founders of the Natural Family Planning Clinics (NPC), the inspirational Margaret France, to come and give our fertility clinic a talk. She explained that the NPC had for many decades been teaching the method of mucus monitoring [1], to predominantly Catholic women, as a means of natural birth control. But on the flip side it can of course be used equally well, as an empowering tool for those that are looking to achieve a pregnancy. That was in 1994, and Margaret and I went on to investigate and publish one of the first papers on ovulatory awareness in women attending a fertility clinic [2].)

Knowing the length of your menstrual cycle will help you track your ovulation so you can plan intercourse. Your cycle length is the number of days between the first day of bleeding of one period (full menstruation, not spotting) and the first day of bleeding of your next period. Cycle lengths can vary between 23 and 35 days. Ovulation happens around 14 days before the first day of your period.

Leading up to ovulation, you may notice changes to your body such as, changes in cervical mucus (as explained above), a boost in libido, cramps, and your body temperature rising slightly after ovulation has occurred.

There are also tools available to help track ovulation such as:

  • Fertility apps.
  • Online calculators like this one.
  • Ovulation detection kits: these are urine tests that detect the luteinizing hormone (LH) and whilst they have been proven to be effective, they are associated with a cost.



Back in the day, one of the first questions doctors would ask couples attending their fertility consultations was: how many times a week do you have sex? I’m pretty sure many would have found that pretty confronting, especially for those who had been trying for years with no success! 

But for the modern demographic and enlightened world of today, we should expect more appropriate questions to be asked such as: do you have an understanding of when you ovulate (using observations, apps, awareness, ovulation kits), and do you have sex at least twice in the days before you expect to ovulate? 

Once you know when you expect to ovulate, you want to aim to have intercourse a couple of times in the two to three days before ovulation. So if you regularly have a 28 day cycle, that would be days 11, 12 and 13. 

Because the takeaway message is, it’s all about timing.


Good to know

We recommend that you seek advice and help from your GP or a fertility clinic if you have been trying for one year and are under the age of 35, or six months if you are 36 years old or older.

There are also tests you can do to check your fertility health, such as an AMH test and Semen Analysis, which you can arrange through your GP or fertility doctor.

At Repromed we provide a first consultation to speak with us about your specific fertility journey. You can find out more about what we cover at this first consultation here.

If you’d like to book in, get in touch with us today.


[1] Betts K. 1984 The Billings Method of Family Planning: An assessment. Studies in Family Planning V15:6 p253

[2] Blake DA, Smith D, Bargiacchi A, France M. (1997) Fertility awareness in women attending a fertility clinic.


Article published May 2023.

Megan Black

Nurse Manager


Megan leads the nursing team through the continually changing face of IVF. She works in a multidisciplinary team, providing the essential organization between the doctors and laboratory and ensuring communication between all departments.

Megan started her IVF nursing career in the United Kingdom, working in two large London clinic’s before returning to New Zealand. She is also the Secretary of Fertility Nurses of Australasia.

I love working with people and see nursing as a vocation, not a job. I usually spend my downtime absorbed in a good book and planning my next travel adventure.