Whether you are planning to conceive or trying to avoid pregnancy – knowledge of your normal menstrual cycle can give you a good indication of the times when you are fertile and when you aren’t.
The Menstrual Cycle – A Brief Summary.
Menstrual cycles on average last 28 days and are calculated from the first day of your period (fresh red bleeding). This first day is Cycle Day1 (CD1). The time from CD1 until ovulation is known as the Follicular Phase (FP). The Follicular phase can also be further divided into menses, and proliferation phase.
Normal menses (aka period or AF – “Aunt Flo”) last anywhere between 2-7 days. During your period, the womb lining (endometrium) is shed to make way for a new, fresh lining to be made. The Proliferation phase follows on from menses until ovulation. During this time, the hormone Oestrogen is dominant. Its levels rise & peak just before ovulation. Oestrogen encourages the endometrium to thicken and has a role in triggering ovulation.
Within the ovaries, there are a large number of follicles, each with the potential to develop a mature healthy ovum or egg. There is constant development and maturation of these follicles, with one dominant follicle being ‘selected’ at the beginning of each menstrual cycle. It is this follicle that will go on to develop a single mature ovum for release and potential fertilisation.
Towards the end of a healthy follicular phase levels of oestrogen trigger another hormone, Luteinising Hormone (LH), to peak and this in turn triggers the release of the mature ovum from the follicle – this is ovulation, and in an average fertile cycle occurs around cd14.
The time from ovulation until the start of a new cycle is known as Luteal Phase (LP), or often also referred to as the “two week wait” (TWW) by those trying to conceive. Following ovulation, levels of oestrogen fall rapidly and progesterone becomes the dominant hormone. The follicle from which the egg was released becomes a “corpus luteum” and secretes progesterone. The endometrium continues to thicken. If the ovum is not fertilised, then the corpus luteum begins to degenerate after approximately 14 days. Levels of progesterone begin to fall and this then triggers the start of menses. The cycle begins again.
What Happens At Conception?
if the egg is fertilised, it implants within the uterine wall (around 8-9 days post ovulation) and begins to secrete the pregnancy hormone human chorionic gonadotrophin (HCG). This signals the corpus luteum to continue secreting progesterone, the endometrium remains and eventually the placenta will take over progesterone production in a healthy pregnancy.
by Lorraine Berry – Midwife