Your usual menstrual cycle is usually interrupted by pregnancy. This means you don’t ovulate or menstruate. The body switches gears, so to speak, and focuses on developing the growing embryo.
However, on rare occasions (usually when women are undergoing fertility treatment), some women do ovulate when they’re already pregnant.
In this article, we’ll explain the four key phases of a woman’s menstrual cycle and then look more closely at what happens during ovulation. Then, we’ll dive deeper into the rare occurrence of superfetation, which happens when a woman becomes pregnant, while already pregnant.
Your Menstrual Cycle: 4 Key Phases
Your monthly menstrual cycle can be divided into four important phases.
- Follicular Phase
- Luteal Phase
The average menstrual cycle is 28 days. However, many women experience shorter cycles (around 21 days) and some women experience longer cycles (up to 35 days). Moreover, many women experience irregular menstrual cycles, which can be caused by many factors. Do not be alarmed if your body doesn’t run like steady clockwork.
What is Ovulation?
During reproductive ages, the ovary releases an egg every month. This event occurs when ovary follicles rupture and release the oocyte which travels to the fallopian tube and becomes an ovum or egg. The rupture of the ovary follicles can cause some light spotting and some women can even feel it happen.
The process of ovulation is controlled by the hypothalamus of the brain and through the release of hormones. This means that ovulation can be impacted by hormone levels and stressors. Hormones affecting this stage are: High levels of Luteinizing Hormone (LH).
After the oocyte is released from the ovary, it moves into the fallopian tube. At this point it is called an ovum or egg. The egg stays in the tube for about 24 hours, waiting for a single sperm to fertilize it.
If the egg is not fertilized during that time, it disintegrates (breaks down) and menstruation (your period) begins 11-16 days later.
Ovulation and Pregnancy: The Fertile Window
For those trying to get pregnant, knowing when you might be ovulating is important. Your most fertile days ("the fertile window") are the 3 days leading up to and including ovulation. This is when you’re most likely to get pregnant. So, having sex then gives you the best chance of ensuring the egg is fertilized by sperm so you become pregnant.
But, as previously mentioned, ovulation is a delicate process. Not to mention, the woman's reproductive cycle is just one side of the equation. Sperm heath is also key in your chances of getting pregnant. If you are hoping to get pregnant, consider using an ovulation predictor kit to identify your fertile window.
When you ovulate, an egg bursts from its follicle in your ovary. That ruptured follicle stays on the surface of the ovary. Over the course of the next two weeks, that follicle transforms into a structure known as the corpus luteum.
The corpus luteum releases progesterone, along with small amounts of estrogen. These hormones maintain the thickened lining of your uterus, in preparation for implantation of a fertilized egg.
When Does Ovulation Happen?
Every woman’s cycle is different. Some of us have longer periods than others, for example. So the timing of ovulation is not always the same in every woman's cycle.
But generally a woman’s entire menstrual cycle is on average 28 days. That said, it can range between 21 to 35 days in adults and from 21 to 45 days in young teenagers. That's why most women track their own cycle with a periods calculator or diary.
The first day of a menstrual cycle is counted from the first day of your menstrual period. You ovulate about 14 days before your period starts.
If your average menstrual cycle is 28 days and the first day of your cycle is Day 1 of your menstrual period, day 14 in your cycle is your day of ovulation, and your most fertile days are days 12, 13 and 14. These are the days pregnancy is most likely to occur.
If your average menstrual cycle is 35 days ovulation happens around day 21 and your most fertile days are days 19, 20 and 21.
Signs of Ovulation
Ovulation often goes completely unnoticed by women. However, when you ovulate and the egg is released, there are signs of ovulation. Some women will observe more keenly than others, these include:
- Your basal body temperature falls: Your basal body temperature drops a little bit just before the egg is released from your ovary. Then, 24 hours after the egg's release, your body temperature rises and stays up for several days.
- Cervical mucus changes: The changes in your discharge over the course of your menstrual cycle also hold clues about when you might be ovulating. If your cervical mucus is:
- Dry or sticky: It’s unlikely you’re ovulating
- Creamy: Ovulation may be coming
- Wet or watery: Ovulation may start soon
- Wet and stretchy (egg white texture): You may be ovulating
- Your cervix softens and opens up: As you approach your most fertile time, your cervix softens. This is sometimes known as having a short, high, open and wet cervix (SHOW).
- You may experience a slight twinge or cramping: “Mittelschmerz” translates literally as “middle pain” and is the name for the slight twinge or cramp that some women experience when the follicle releases the egg.
- Spotting: When the ovaries release the egg, a tiny follicle ruptures to allow the egg to be released. This can be a cause of spotting for a day or so.
What Usually Happens When You Get Pregnant?
When you get pregnant, a fertilized egg is implanted in your uterus lining (the endometrium) and grows into an embryo.
The fertilized egg itself produces the hormones that are necessary to maintain the corpus luteum and it keeps producing progesterone to maintain the thickened lining of the uterus (endometrium). Among the hormones produced by the fertilized egg is human chorionic gonadotropin (HCG), which is detected in urine during a pregnancy test.
The hormones that are released after you get pregnant are unique and different from your usual menstrual cycle. Pregnancy is characterized by a sudden, dramatic in estrogen and progesterone. There are also other hormones that vary from normal amount and function.
These hormonal changes help prepare the woman’s body for a growing fetus and a healthy pregnancy. They also “interrupt” the usual menstrual cycle so that you don’t shed the lining of your womb (menstruation) and the whole menstrual cycle stops cycling,
According to this article in the New York Times, “Ordinarily, the release of eggs ceases once a woman is pregnant, and the hormonal and physical changes of pregnancy work together to prevent another conception.”
The One Rare Exception: Superfetation
Based on this, it would seem completely impossible for a woman to ovulate after getting pregnant. This is normally the case. However, occasionally our bodies break the rules...
The most likely cause of a woman ovulating after getting pregnant is that she’s taking hormone-affecting medication, like undergoing fertility treatment.
Superfetation is the term applied to a pregnancy that occurs when a woman is already pregnant. While it’s common to certain animales (e.g. rodents, rabbits, horses, sheep, kangaroos, badgers and mink), it is highly rare in human women. So rare, indeed, that there aren’t even statistics.
For superfetation to occur, a series of very unlikely events must happen. These include:
- You ovulate while already pregnant
- There is sperm present to fertilize the egg
- That egg also needs to implant on the womb
The first step alone is unlikely to happen because the hormones released during pregnancy usually stop ovulation. Of the few cases of superfetation reported, the cause of this has usually been that the woman in question was undergoing fertility treatment.
To give you a real sense of how rare this is, according to a 2008 paper published in the European Journal of Obstetrics and Gynaecology, there have only been 10 cases recorded in medical history.
Other Factors that Can Disrupt Your Menstrual Cycle
Your menstrual cycle is a very delicate process and fluctuations in hormone levels can disrupt it. Odds are most of us have experienced a late period due to stress, or even missed periods.
Some of the factors that can disrupt your menstrual cycle can also be cause for medical concern. But that doesn’t mean you should panic. Here are some of the many things that can have an impact:
- Stress & anxiety: Stress can throw your body for a loop and this includes your menstrual cycle.
- Exhaustion: Feeling jet lagged or suffering from insomnia? It’s not unusual that this would impact your cycle.
- Diet: Nutrition is key for general wellbeing, including reproductive health. People with eating disorders may find their cycles disrupted.
- Polycystic ovary syndrome (PCOS): Women with PCOS may have infrequent or prolonged menstrual periods or excess male hormone (androgen) levels. The ovaries may develop numerous small collections of fluid (follicles) and fail to regularly release eggs.
- Uterine fibroids or polyps: Fibroids are benign growths that can cause heavy bleeding and disrupt your cycle. They can also cause pain and discomfort.
- Birth control & other medications: Hormonal birth control deliberately sets out to interrupt your natural menstrual cycle in order to prevent pregnancy. Side effects of other medications can also disrupt women’s cycles.
- Perimenopause: This is the final stage before menopause (when periods cease completely) and is usually characterized by an irregular menstrual cycle as periods gradually stop. Menopause is diagnosed when you go 12 months without a period.
When to See a Doctor
If you experience any of the following, it’s worth scheduling a check-up with your doctor to discuss your cycle:
- Heavy periods with a lot of clotting (especially clots larger than a quarter)
- Irregular periods
- Spotting between periods accompanied by abdominal pain or cramping
- Pain or a burning sensation when peeing
- Unusual vaginal discharge and/or redness and itchiness
Even if you don’t have any of the above symptoms, always visit the doctor in the following situations:
- If you think you’re pregnant or are trying to get pregnant: You should always see a doctor as soon as you think you might be pregnant to be administered a pregnancy test.
- If you experience inconsistent spotting: If spotting seems to happen frequently and randomly, you should definitely look into it.
- Bleeding or spotting begins after unprotected sex: Unprotected sex can put you at risk for STIs and other infections so if you notice spotting after unprotected sex, it’s wise to visit a doctor.
- Post-menopausal vaginal bleeding: You’ve been through menopause and you experience vaginal bleeding.