Understanding Your Menstrual Cycle
To most women, their menstrual cycle is a nuisance, unless trying for a baby. Understanding your menstrual cycle can help improve your fertility and chances of having a baby. Below are extracts from my fertility book on when to try and conceive a baby naturally.
The word ‘menstrual’ comes from the Latin for ‘month’ and the word ‘month’ comes from the Latin for ‘moon’. In Chinese medicine the menstrual cycle is also related to the moon. Historically, a woman’s menstrual cycle would have followed the lunar cycles. The moon is yin in Chinese medicine, as is a woman and the blood that she releases through her menstrual cycle. A normal menstrual cycle is around 28-29.5 days long, which follows the moon’s length of change.
The menstrual cycle is made up of two sub-cycles: one for the ovaries and one for the uterus. Regulating both of these cycles is key to good fertility. The main hormones involved in the ovary cycle are follicle stimulating hormone (FSH) and luteal hormone (LH), whilst the main hormones involved in the uterus cycle are oestrogens (oestradiol) and progestins (progesterone).
The ovarian cycle is made up of two phases; the follicular phase which is yin and the luteal phase, which is yang. The follicular/yin phase is the maturing of a dominant follicle that contains the egg. The luteal/yang phase is the release of the egg into the fallopian tube, insemination of the egg by a sperm, the moving of the egg down the fallopian tube and implantation of the fertilised egg into the uterus wall (endometrial lining). The uterine cycle involves the breakdown of the uterus lining, when a woman has her menstrual bleed in the initial follicular/yin phase and the building up of the uterus lining to its peak in the luteal/yang phase.
At the start of a women’s menstrual cycle, the entire uterus lining shreds due to a lack of both oestrogens and progestins that are needed to sustain it, leaving only the basal layer. A good period flow should last between 5-7 days and be heavy for the first 3-5 days, then reduce to medium then light. Typically, a woman will loose 50-90ml of red blood without clots. If the blood is dark, is not heavy on day 1 or has clots, then this is an indicator of a problem with the menstrual cycle. Premenstrual symptoms, commonly perceived as normal, are also indicators of problems with the menstrual cycle and therefore fertility. Acupuncture is very good at treating premenstrual symptoms and problems with menstrual blood flow, thereby improving the menstrual cycle and fertility.
As bleeding takes place, the hypothalamus releases gonadotropin-releasing hormone (GnRH), which causes the pituitary gland to start the production of FSH. This in turn stimulates the follicles to grow. Yin starts to increase up until ovulation. The number of follicles a woman has is fixed from birth. It is possible to measure the number (and quality) of eggs from an AMH test. It takes around 120 days for an egg to develop from start to finish. Follicles sit in a procession and their quality is affected by a woman’s underlying health. The better their health, the better the egg will be that’s in the follicle. Between 10-20 follicles are stimulated in one menstrual cycle. As the follicles mature, one becomes dominant and releases estrogens, whilst the others fade away. There are three oestrogens; oestradiol, oestrone and oestriol. Oestradiol is the most abundant of the three and therefore the main one to consider in fertility.
As oestrogens surge, they repair and regenerate the endometrial lining within the uterus. The uterus lining will gradually thicken reaching its maximum thickness around day 21. The optimal thickness is 8+mm with a triple lining. This triple lining is the three layers that make up the uterus wall. As one follicle becomes dominant, oestrogen levels rise steeply increasing the thickness of the endometrial lining and the start of LH production, which helps the egg to ripen and eject from follicle sack. The mature egg then releases inhibin, which turns off the production of FSH. At around day 14-15 in a typical 28-29.5 day cycle, there is a massive release of LH from the pituitary gland.
The LH surge typically occurs 34-36 hours before ovulation. This LH surge is used by ovulation kits to test when it’s the right time for couples to have intercourse. However, surges in LH can vary from woman to woman, The LH surge also pulsates, so it’s not continuous and therefore ovulation kits may not always detect the LH surge. I would recommend watching your body’s own signs of ovulation instead of using ovulation kits, which are often expensive, inaccurate and can potentially cause stress.
The surge in LH causes the release of the egg from the ovary. At this point, the follicle is around 18-25mm in size and has reached maturation. This occurs roughly 9 hours after the LH peak. At this point yang starts to grow and becomes the dominant force in the luteal phase. Yang is involved in fertilisation, the movement of the egg along the fallopian tube and its implantation into the uterus wall.
The high LH levels that trigger ovulation also promote the production of the main progestin hormone; progesterone. Progesterone maintains the flow of blood supply to the uterus lining, thereby maintaining it. It also tells the pituitary gland to stop producing FSH and increases the production of immune cells that aid implantation. Progesterone levels remain high for about a week and drop off if pregnancy is not achieved, causing the disintegration of the uterus lining and the period to begin.