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.

Dr. Erika B. Johnston-MacAnanny, a fertility specialist at SGF Richmond, explains the menstrual cycles, outlines what they might indicate for your fertility potential, and provides insight into what this tells your doctor about your reproductive health.  

Medical contribution by Erika B. Johnston-MacAnanny, M.D.

Erika Johnston-MacAnanny, M.D., FACOG, is board certified in both obstetrics and gynecology and reproductive endocrinology and infertility. Dr. Johnston-MacAnanny sees SGF patients in the Richmond – Stony Point and Richmond – Henrico Doctors’ – Forest locations.

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 where 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 periodis day 1 of your cycle and the start of the follicular phase.  Patients note this as the first day they see full flow menstrual blood.  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, granulosa cells which line the follicle release estrogen (also known scientifically as estradiol) which stimulates growth and thickening of the uterine lining. The follicular phase concludes at the start of ovulation – the process of releasing a mature egg from the dominant follicle. The length of the follicular phase is variable between individuals, resulting in most variations of total cycle length.   Patients with low ovarian reserve may note a shortened follicular phase whereas women with polycystic ovarian syndrome may have an extended follicular phase. 

The luteal phase starts after ovulation and continues until the onset of the next menses. During this phase, the ovary releases progesterone which transforms the uterine lining and opens the window of implantation – the time during which the embryo can attach to the uterus. If pregnancy does not occur, the progesterone levels drop and bleeding occurs as the lining is shed. The luteal phase is usually between 12-14 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 predictable manner. Hormonal imbalances can affect if and when ovulation occurs during your cycle. Without ovulation, pregnancy cannot occur naturally. 

is my period normal infographic

Normal menstrual cycle:

Days: 24 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 24 days

Ovulation indicator: Ovulation may not have occurred or occurred much earlier than normal

What do short cycles tell your doctor? Shortened cycles can be an indication that the ovaries contain fewer eggs than expected. This is typically a pattern seen in the years leading up to perimenopause. Alternatively, a short cycle could indicate that ovulation is not occurring. If blood work confirms this to be the case, conception without assistance can be more difficult.

What causes a shorter cycle? As a woman ages, her menstrual cycle shortens. Our eggs are a nonrenewable resource, we cannot grow more.  As the remaining number of eggs available in the ovary decreases, their quality also declines. These dysfunctional ovaries lose their ability to effectively communicate with the brain. Additionally, the brain needs to release more follicle stimulating hormone (FSH) to stimulate these abnormal eggs to mature and typically does so even in the luteal phase prior to the cycle being tracked, resulting in a shortened follicular phase and early ovulation.  

As a result, the dominant follicle is ready for ovulation earlier in the follicular phase and produces a shorter cycle length. In addition, sometimes bleeding can occur even when ovulation does not occur, which may appear as shortened and irregular cycles

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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 regularly, which can make conception difficult.

What causes long menstrual cycles? Longer cycles are caused by a lack of regular ovulation. During a normal cycle, the fall of progesterone leads to  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 unopposed estrogen. The lining gets so thick that it becomes unstable until it eventually sheds and bleeding occurs. This bleeding can be unpredictable, and oftentimes very heavy and lasts a prolonged period.  Heavy flow may result in health conditions such as low blood count, or anemia, for the patient. 

There are many causes of oligo-ovulation, the medical term used to describe when ovaries do not grow a dominant follicle and release a mature egg on a regular basis.  Polycystic ovary syndrome (PCOS), the most common cause for oligo-ovulation, is a syndrome resulting from disordered brain communication and stimulation from the anterior pituitary. This can result in an imbalance in the sex hormones and failure to grow a dominant follicle and unpredictable or absent ovulation. In addition, 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.  The latter conditions are typically treated with oral medication to correct the hormonal imbalance. 

When menstrual bleeding lasts more than 5-7 days:

Days: More than 7 days

Ovulation indicator: It is possible that there is a hormonal problem resulting in a delay in follicular growth or a structural problem in the uterus making the lining unstable.

What do longer cycles tell your doctor? Prolonged bleeding tells your doctor that the ovary is not responding to the brain signals to grow a lead follicle. This can be a sign of a delayed or absent ovulation. Alternatively, there may be something disrupting the lining of the uterus.

What causes long periods of bleeding? There are many causes of prolonged bleeding. From a hormonal perspective, what stops a woman’s period is estrogen from the growing follicle. If follicular growth is not occurring regularly, then prolonged and irregular bleeding can occur. Intermenstrual bleeding or prolonged bleeding may be caused by structural problems like 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 occurring

What does a lack of menstruation tell your doctor? Either ovulation is not occurring or there is something blocking menstrual blood flow. The patient will have difficultly conceiving 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. Hypothalamic amenorrhea is a potential cause, as well as any of the hormonal imbalances that can cause irregular cycles can also stop the cycles completely.  It is common for women who are considered underweight or overweight 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 or lose weight will see the return of a more predicatble menstrual cycle. 

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 menstrual cycle, no matter the amount of time you have been trying to conceive, you should be evaluated by a specialist. Irregular or absent ovulation makes conception very difficult without intervention. 

For women with regular cycles, you should see a fertility specialists if you are:   

  • Under 35 with regular cycles, unprotected intercourse and no pregnancy after 1 year 
  • 35 to 39 with regular cycles, unprotected intercourse and no pregnancy after 6 months 
  • 40 or over with regular cycles, unprotected intercourse, more immediate evaluation and treatment are warranted 

Editor’s Note: This post was originally published in October 2014 and has been updated for accuracy and comprehensiveness as of June 2024.

For more information about your menstrual cycle or to schedule an appointment with one of our physicians, please speak with one of our New Patient Liaisons at 877-971-7755 or fill out this brief form.