Medical Contribution by: Stephanie Beall, M.D., PhD
One of the most common questions OB/GYN’s have for their patients is “When was the first day of your last period?”. The answer to this question may feel like part of the usual routine at your annual OB/GYN appointment. If you have been trying to conceive without success, the answer could provide important insight into factors central to the menstrual cycle and conception such as hormonal imbalances and ovulation.
What is a menstrual cycle?
Hint, it is more than just your period. The menstrual cycle is a series of changes a woman’s body goes through each month whereby the ovary releases an egg and the uterus prepares for pregnancy. The cycle can be divided into two phases: the follicular phase and the luteal phase.
The first day of your menses – or period – is day 1 of your cycle and the start of the follicular phase. During this phase, follicle stimulating hormone (FSH), is released from the brain to stimulate the development of a single dominant follicle which contains one egg. During its maturation, the follicle releases estrogen which stimulates the thickening of the uterine lining. The follicular phase concludes at the start of ovulation. The length of this phase may vary, resulting in most variations of total cycle length.
The luteal phase starts with ovulation and continues until the onset of menses. During this phase, the ovary releases progesterone which matures the uterine lining and prepares it for the implantation of an embryo. If pregnancy does not occur, the progesterone level drops and bleeding occurs. The luteal phase is usually around 14 days.
Does the length of a menstrual cycle matter?
The length of a menstrual cycle is determined by the number of days from the first day of bleeding to the start of the next menses. The length of your cycle, while not on any form of birth control, can be a key indicator to hormonal imbalances and whether or not ovulation is occurring in a regular manner. Hormonal imbalances can affect if and when ovulation occurs during your cycle. Without ovulation, pregnancy cannot occur.
Normal menstrual cycle
Days: 21 to 35 days
Ovulation Indicator: Regular cycles indicate that ovulation has occurred
What Do Normal Cycles Tell Your Doctor? Cycles of a normal length suggest regular ovulation and that all of the sex hormones are balanced to support natural conception.
Short menstrual cycle
Days: Less than 21 days
Ovulation Indicator: Ovulation may not have occurred or occurred earlier than normal
What Do Short Cycles Tell Your Doctor? Shortened cycles can be an indication that the ovaries contain fewer eggs and that menopause may be approaching. Alternatively, a short cycle could indicate that ovulation is not occurring. If blood work confirms this to be the case, natural conception can be more difficult.
What Causes a Shorter Cycle? As a woman grows older, her menstrual cycle shortens. As the number of eggs available in the ovary decrease, the brain releases more follicle stimulating hormone (FSH) to stimulate the ovaries to develop a follicle. This results in earlier development of the follicle and earlier ovulation and therefore shortened cycles. In addition, sometimes bleeding can occur even when ovulation does not occur, and this may appear as shortened cycles.
Long or irregular menstrual cycle
Days: More than 35 days
Ovulation Indicator: Ovulation is either not occurring or occurring irregularly
What Do Longer Cycles Tell Your Doctor? Longer cycles are an indicator that ovulation is not occurring or at least not in a regular manner which can make conception difficult.
What Causes Long Menstrual Cycles? Longer cycles are caused by a lack of regular ovulation. During a normal cycle, it is the fall of progesterone that brings upon bleeding. If a follicle does not mature and ovulate, progesterone is never released and the lining of the uterus continues to build in response to estrogen. Eventually, the lining gets so thick that it becomes unstable and like a tower of blocks, eventually falls and bleeding occurs. This bleeding can be unpredictable, and oftentimes very heavy and lasting a prolonged period of time.
There are many causes of anovulation, the medical term used to describe when ovaries do not release mature eggs on a regular basis. Irregularities with the thyroid gland or elevations of the hormone prolactin can disrupt the brain’s ability to communicate with the ovary and result in anovulation. In addition, polycystic ovarian syndrome (PCOS), a syndrome caused by imbalanced sex hormones, can also cause failed ovulation. Not only do these hormonal imbalances lead to problems with ovulation and therefore fertility, but they may also increase the risk of miscarriage.
When menstrual bleeding lasts more than 5-7 days
Days: More than 7 days
Ovulation Indicator: It is possible that ovulation has not occurred
What Do Longer Cycles Tell Your Doctor? Prolonged bleeding tells your doctor that either ovulation is not occurring regularly, there may be something disrupting the lining of the uterus, or there is a problem forming blood clots.
What Causes Long Periods of Bleeding? There are many causes of prolonged bleeding, for example, if ovulation is not occurring regularly, irregular bleeding and prolonged bleeding can occur. Intermenstrual bleeding or prolonged bleeding may be caused by polyps, fibroids, cancer or infection within the uterus or cervix. In these situations, should an embryo enter the uterus, implantation can be compromised resulting in lower pregnancy rates or an increased chance of a miscarriage. Although rare, a problem with blood clotting can also cause prolonged bleeding and this requires evaluation and care by a specialist.
What if I never menstruate?
Days: Rarely or Never
Ovulation Indicator: Ovulation may not be occuring
What does a Lack of Menstruation tell your Doctor? Either ovulation is not occurring or there is something blocking blood flow. The patient will have difficultly conceiving naturally without intervention.
What Causes Cycles to Stop Occurring? When a woman does not have a period, this can be caused by a failure to ovulate. It is common in women who are considered underweight by the body mass index (BMI) standards to stop having a cycle. The body requires a certain level of body fat for reproduction and menstrual cycles to occur, and many women who are able to gain weight will see the return of their cycle. Learn about hypothalamic amenorrhea. Also, any of the hormonal imbalances that can cause irregular cycles can also stop the cycles completely.
Weight is not the only cause to consider. There are several other causes that should be evaluated as well. If a woman has never had menstrual bleeding, there may have been a problem with the normal development of the uterus or the vagina. If a woman had menstrual cycles previously, but then stopped, this could be due to a problem with the uterus itself, like scar tissue inside the cavity, or may be due to premature menopause. If the uterus has not formed or if menopause has occurred, pregnancy is not possible. If the absence of menses is due to scar tissue inside the uterus, then this scar tissue will need to be removed as it can interfere with implantation.
If you do not have a normal monthly menses, no matter the amount of time you have been trying to conceive, you should be evaluated by a specialist. Irregular or no ovulation makes conception very difficult without intervention. Any woman less than 35 years of age with normal cycles who has not gotten pregnant after a year of trying should see an infertility specialist. If you are 35 or older with a normal menstrual cycle and have been trying for 6 months without success, you should seek care as well. Normal menstruation indicates that you are ovulating; however, there are other reasons why you may not be able to get pregnant, and these should also be evaluated.
Editor’s Note: This post was originally published in October 2014 and has been updated for accuracy and comprehensiveness as of March 2019.
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