What is a "normal" menstrual cycle?
Understanding the menstrual cycle is an important part of trying to conceive. A menstrual cycle begins with the first day of a period (full flow bleeding) and ends with the start of the next period. The average length of the menstrual cycle is 28 days but can vary widely among patients (21-to-35 days is considered within the normal range). If your cycle lengths vary less than a week month to month, this is generally thought to be "regular."
What happens during a menstrual cycle?
The menstrual cycle can broken down into the following parts:
- Menstruation and the follicular phase: Menstruation is what you experience as your period and results from the shedding of the lining of your uterus if you are not pregnant. During the follicular phase, your brain signals your ovaries to grow an egg, which is housed in a fluid-filled sac called a follicle). Generally, only one follicle develops each month. Estrogen levels rise g during this process and also cause the uterine lining to thicken in preparation for possible implantation of a pregnancy. In a 28-day cycle, the follicular phase usually lasts from days one-to-14.
- Ovulation: This is the process of your ovary releasing a mature egg from the follicle that has been developing over the last two weeks. This happens when there is a rise in Luteinizing Hormone (LH), which is a hormone made by your brain to communicate with your ovary. Ovulation typically happens ~14 days before the start of your next period.
- The luteal phase: This phase lasts from the time of ovulation to the start of the next period, which is typically 14 days though there may be some variation person to person. During this phase, the egg that was released during ovulation can be fertilized by sperm. When an egg becomes fertilized, it becomes an embryo, which can then implant in the uterine lining (also called the endometrium) and result in pregnancy. The hormone progesterone is an important regulator of your uterine lining's ability to sustain a pregnancy and will be elevated during the luteal phase. If there is no pregnancy, the drop in progesterone triggers the next period to start.
What if my periods are not "regular"?
There are many causes of irregular periods. One of the most common causes is polycystic ovary syndrome (PCOS), which is caused by an excess of male hormones and lack of ovulation. This hormonal imbalance can cause unscheduled bleeding among other symptoms such as facial hair growth and acne. Other causes of irregular periods include thyroid disorders, uterine fibroids, or uterine polyps. If you are not having regular periods, your doctor will likely evaluate for these possible causes as part of your fertility testing.
What about heavy periods?
Even if their periods come at a predictable time each month, some patients may experience very heavy or prolonged periods lasting longer than seven days. Patients with heavy periods often soak through pads and tampons within one to two hours, have to change pads or tampons overnight, or have symptoms of low blood count such as fatigue and dizziness. Common reasons for these symptoms may include irregular ovulation, fibroids, adenomyosis, and uterine polyps. An ultrasound is often the first step for identifying these underlying issues and is performed as part of the basic fertility evaluation.
So what does this mean for trying to conceive?
In order to maximize chances of conception, sperm is ideally already present within the female reproductive tract when the egg is released. This means that the chances of pregnancy are highest the day before ovulation, with the fertile window overall lasting from five days before ovulation to the day of ovulation.