The Menstrual Cycle
Throughout recorded history, there have been many superstitious beliefs with regards to menstruation. If a woman does not have a regular, monthly period there are typically a handful of reasons why. The focus of this blog is to help patients understand the normal menstrual cycle.
A normal menstrual cycle typically occurs every 24-35 days. It is divided into two phases, the follicular phase when an egg grows inside a follicle and the luteal phase when the follicle becomes a corpus luteum and makes progesterone. The end of the follicular phase and beginning of the luteal phase is marked by ovulation.
The menstrual cycle begins with the first day of full flow bleeding, what we call the first day of the last menstrual period of cycle day one. At the very beginning of the period certain hormone levels in our blood should be low. Estradiol, a type of estrogen produced by cells in the ovary, and Follicle Stimulating Hormone (FSH) a hormone produced by the brain, are low. It is this low estradiol from the ovary that signals the brain to start releasing the hormone FSH. The FSH talks to the ovaries and signals a follicle to grow. Inside each follicle is an egg and surrounding that egg are cells that produce estradiol. It is important to understand that there are numerous follicles in each ovary, depending on the woman’s age and her genetic make-up. However, only one follicle, with one egg inside, is chosen to grow and ovulate each month. The other eggs die off at the end of that month. As the FSH is signaling the follicle to grown and subsequently the egg to mature, the cells surrounding the egg are producing more and more estradiol. This estradiol is what increases the thickness of the uterine lining. Once the estradiol reaches a certain threshold level, it signals to the brain to stop making FSH and start making luteinizing hormone (LH). When the brain releases LH, this tells the ovary to release the egg from the follicle, in other words, it tells the egg to ovulate. Once the egg is released from the follicle, ovulated, what remains of the follicle is called the corpus luteum. This corpus luteum produces progesterone. If the egg is fertilized by sperm, implants into the uterine lining, and starts releasing pregnancy hormones, this corpus luteum continues to make progesterone and you have a pregnancy. If you do not have a pregnancy, the corpus luteum degenerates and there is a drop in progesterone that causes the woman to shed her uterine lining and have a period. If something with this process is not working, and a woman is not ovulating, she is not going to have a regular period. If this irregular ovulation is the cause of the patient’s irregular period, it is our job to determine why that is occurring. In doing so, we try to help the patient ovulate normally for many reasons one of which is to try and conceive.
Kari Sproul von Goeben, M.D.