Learn about your cycle and the hormones involved!
Understanding your PdG (progesterone metabolite) levels starts with understanding your cycle. Like most women, the fertility talk, abbreviations, and charts and numbers can get a little confusing! But it’s really not that complicated.
Your cycle consists of two main phases: the follicular phase and the luteal phase. The follicular phase is the first half of the cycle and is comprised of menstruation (we all know what that is!) and the fertile window (the time that it’s possible to get pregnant if you are trying to conceive). It ends with the main cycle event: ovulation! The luteal phase occurs after ovulation and is when the body needs to be ready to receive a fertilized egg if conception has occurred.
Probably the most well-known part of your cycle is menstruation, which occurs during the follicular phase. This is where your uterus sheds its lining - which is primarily comprised of blood, endometrial cells, and mucus.
The start of this part of the cycle varies from woman to woman...and it is supported by things happening from cycle day one. At the start of the cycle, glands release FSH (follicle-stimulating hormone). This hormone stimulates 5-20 follicles in the ovaries. These follicles each have an egg inside ready to roll! One lucky follicle will have an egg that matures and the rest will die (unless you have twins). The developing follicles starts producing high amount of estrogen, which helps prepare the uterine lining for conception. Once estrogen gets to a certain level, it triggers what is commonly referred to as the “LH surge” where luteinizing hormone spikes and causes the winning follicle to rupture!
Ovulation is the release of a mature egg (caused by our friend LH) from the ovary to the fallopian tube. The egg breaks free from the follicle inside your ovary and travels down into the fallopian tube where it waits for sperm to arrive. With or without the sperm, it travels slowly through the tubes and into the uterus. The lifespan of this egg is only about 24 hours long, so unless it meets sperm, it dies.
While not as commonly known, the luteal phase is arguably the most important phase in your cycle if you’re TTC. Remember the follicle that matured that special egg and released it into the fallopian tube? This follicle is most important in the Luteal Phase. The follicle transforms into the corpus luteum, a new structure that now releases progesterone. The progesterone sticks around and causes the uterus lining to thicken so the fertilized egg (if it has met with a sperm) can properly implant in the uterus. If conception does not occur, the follicle dies after 10-14 days. Because the follicle dies, the source of progesterone also subsides - this progesterone decline causes the uterus lining to fall away and we are back at square one: menstruation.
If conception has occurred, the fertilized embryo rescues the corpus luteum from dying so that it can keep producing progesterone up until about week 8 when the placenta takes over progesterone production. If the corpus luteum fails to produce enough progesterone, the uterine lining may not adequately support the embryo, which can lead to lack of successful conception or early pregnancy loss.