All about your hormones and fertility signs

Your hormones and fertility signs

Each of the fertility signals that you observe when you chart your fertility corresponds to a hormonal process and the presence of hormones in your bloodstream. Oestrogen, luteinizing hormone and progesterone are the hormones that are responsible for the signals you observe when charting your fertility signs.


Oestrogen is high before ovulation and dominates the pre-ovulatory, follicular phase of your cycle (the days from the end of your period through to just before you ovulate).  

Oestrogen does the following:

  1. Builds up your endometrium so that a fertilized egg can find nourishment and implant. Your endometrium is the lining of your uterus which you shed each month as a period if you are not pregnant.
  2. Produces your cervical fluid which is necessary for guiding and nourishing the sperm on its travels to your fallopian tubes where your egg may be fertilized.
  3. Causes your cervix to soften and open so that the sperm may enter and reach your fallopian tube for fertilization.
  4. Oestrogen signals the release of Luteinizing Hormone (LH) which is needed to trigger ovulation.

Luteinizing Hormone

Luteinizing Hormone peaks before ovulation and is the hormone responsible for triggering the rupture of the ovarian sac that releases the egg at ovulation.


Progesterone is high after ovulation and during pregnancy it dominates the post-ovulatory, luteal phase of your cycle (the time from post ovulation until you get your period).

After ovulation, progesterone is produced by the corpus luteum (the remains of the ovarian follicle that houses your ovum or egg after ovulation) and is present in dramatically higher amounts.

Progesterone plays the following roles:

  1. Makes the lining of your uterus soft and spongy so that your fertilized egg can latch onto it and implant.
  2. Causes your basal body temperature to rise after ovulation so that it can be measured with a BBT thermometer.
  3. Is needed to support and sustain a pregnancy.
  4. Causes your BBT to stay elevated throughout pregnancy.