Periods during the perimenopause … what can happen?
Perimenopause marks the transition from the reproductive years, when a woman regularly releases an egg each month, to menopause, the stage when egg release ceases entirely. This period of change can bring about noticeable shifts in the menstrual cycle, often beginning in a phase known as the 'late reproductive stage,' even before perimenopause officially starts.
Hormonal Interplay and Cycle Length:
The menstrual cycle length is influenced by the growth and development rate of follicles (immature eggs) and their quality. This process is regulated by a complex interplay of hormones:
Follicle Stimulating Hormone (FSH): Produced by the pituitary gland in the brain, FSH stimulates the ovaries to grow follicles.
Inhibin: This hormone, produced by developing follicles, informs the pituitary gland about the number of growing follicles. High levels of inhibin indicate a sufficient number of developing follicles, prompting the pituitary to release less FSH.
The Late Reproductive Stage:
During the late reproductive stage, the quality of the eggs start to decline. It is thought that possibly because the quality is low they produce less inhibin, so the feedback mechanisms is less reliable and there are variations in oestrogen production from the developing follicles. This phase is a precursor to perimenopause and can be identified by changes in the regularity and nature of menstrual cycles.
Aging and Follicle Count:
As a woman ages, the number of follicles in the ovaries decreases, but also the quality decreases. During perimenopause a lot of follicles will enter the early stages off follicular development but will die (called atresia) very early on in the process. This reduction in mature follicles can be observed through an ultrasound scan, which counts the visible follicles. In reproductive-aged women, there are typically 20-150 growing follicles in the ovaries at any given time, though only those larger than 2mm are visible on the scan.
Reduction in Follicles and Changes in FSH Levels:
As the total number of follicles (immature eggs) in the ovaries decreases, the production of the hormone inhibin also declines. In response, the pituitary gland releases more follicle stimulating hormone (FSH). Elevated FSH levels accelerate the development of the remaining follicles, leading to earlier ovulation, sometimes before the typical 14-day mark. This can shorten menstrual cycles, often one of the first signs of perimenopause.
Increased Follicle Recruitment and Oestrogen Levels:
Higher FSH levels also stimulate the recruitment of a larger number of follicles each month. These follicles produce oestrogen, which means that during perimenopause, contrary to popular belief, oestrogen levels can be as high or even higher than those in younger women. This trend continues until approximately two years before menopause. Elevated oestrogen levels can cause heavier periods.
Anovulation and Irregular Periods:
As the quality and quantity of follicles further diminish, the frequency of anovulatory cycles (cycles where no egg is released) increases. This leads to irregular periods, including missed periods or extended intervals between them.
Summary:
Perimenopause involves complex hormonal fluctuations that impact menstrual cycles. Initially, shorter cycles and heavier periods may occur due to higher FSH and oestrogen levels. As follicle numbers decline further, cycles become more irregular, with missed periods becoming more common.
Understanding these changes can help women better anticipate and manage the symptoms of perimenopause. If you're experiencing significant changes in your menstrual cycle, consulting with a healthcare provider can offer valuable guidance and support.