The lining of the uterus, called the endometrium, thickens during each menstrual cycle in response to the hormone oestrogen. Progesterone levels begin to rise around the time of ovulation, changing the endometrium to make it ready for the implantation of a fertilised egg. If conception doesn't take place, the levels of progesterone and oestrogen fall, causing the endometrial lining to be shed.
Oestrogen breakthrough bleeding
Whenever oestrogen rises the endometrium responds. Oestrogen breakthrough bleeding is the result of high levels of oestrogen and sometimes occurs before the follicle goes on to ovulate. Alternatively the follicles may not develop as they should and remain in a state of chronic stimulation so that the endometrium continues to build; when the endometrium outgrows its blood supply, breakthrough bleeding occurs.
Breakthrough bleeding indicates potential fertility and may be associated with other symptoms such as visible mucus or a slippery sensation. Bleeding may be prolonged and heavy, or may be experienced as a day or two of light bleeding or spotting.
Oestrogen withdrawal bleeding
When a follicle containing the ovum (egg) begins to develop it produces oestrogen, which causes the endometrium to start thickening. But sometimes the follicle doesn't fully mature, and there is no ovulation. The follicle breaks down so the level of oestrogen drops, the endometrium is no longer supported and bleeding can occur. This bleeding can be profuse, perhaps with clots, and it may go on for some time, or it may be light or just spotting.
Oestrogen withdrawal bleeding and breakthrough bleeding can happen at times of fluctuating oestrogen levels, such as during puberty, when breastfeeding, after you stop taking hormonal contraception, and as you approach menopause. If in doubt, consult your Billings Ovulation Method teacher™ who will advise you if you need to seek medical investigation of unexplained bleeding.
This may happen about a week after conception when the fertilised ovum implants into the endometrium.
Any unexplained bleeding should be investigated. The next section looks at abnormalities in your pattern of cervical mucus and your menstrual cycle that should be investigated.