Birds and the Bees Revisited: Part 1- The Menstrual Cycle

Nov 1 2010 in Mind & Body by Anne Cabrinha, M.S., L.Ac., FABORM

As an acupuncturist, many patients come to me for fertility support. One of the first things we discuss is timing of intercourse and our “fertile window.” This three-part blog will cover the basics of the menstrual cycle, how to predict ovulation and the best time to try to conceive. For must of us, high school was the last time we had sex-ed. I think it’s really helpful to review the basics and some finer points as an adult.

OK, let’s begin. The menstrual cycle can be divided into three phases described below. In each phase, changes in both our ovaries and our uterus are preparing for possible pregnancy. These changes are orchestrated by a handful of hormones, including progesterone, estrogen, lutenizing hormone (LH) and follicle stimulating hormone (FSH).

Follicular Phase: This phase begins on the first day that we begin our period, lasts until ovulation, and varies in length. In a 28-day cycle this phase lasts from day 1-13. It is more variable in length than the other phases and accounts for the difference when cycles are shorter or longer than 28 days. During this phase, the lining of our uterus (also called the endometrium) sheds and we have our period, consisting of cervical mucus, vaginal secretions, endometrial tissue and blood. Once bleeding stops, the endometrium begins to thicken as estrogen levels rise. Meanwhile, follicle stimulating hormone (FSH) helps a few eggs within our ovaries begin to grow and mature in sacs called follicles (hence follicular phase).

Ovulatory Phase: Ovulation is the release of one mature egg from a follicle into one of the fallopian tubes that lead to the uterus. Ovulation usually occurs on day 14 of a 28-day cycle with a quick surge of lutenizing hormone (LH). This is the hormone that is tested in an ovulation predictor kit (OPK). Sperm travels up from the vagina, through the cervix (the opening of the uterus), through the uterus and into the fallopian tubes where the sperm meet the egg and conception occurs.

Luteal Phase: This phase lasts about 14 days, between ovulation and the first day of our period. It is the most consistent phase in length. Women with a 24-day cycle or a 32-day cycle, for example, will both have a luteal phase of 14 days. During the first part of this phase, the endometrium continues to thicken with nutrients in response to progesterone, ready to receive a fertilized egg. In the second half of this phase, progesterone and estrogen levels begin to fall and our period begins again, marking the first day of the follicular phase.

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