Ovulation is the key, most important event that determines our cycle, its length, the fertile days, the period duration, and there is so much we don’t know about it. While we mostly focus on our periods to check our cycles, we should be focusing on ovulation! In fact, the non fertilized ovulated egg is what triggers our period and governs our cycle.
What is ovulation?
Put simply, ovulation is the release of the matured egg from the ovary to the Fallopian tube. Eggs develop for several months in follicles or sacs before ovulation. The hormones’ ups and downs across several cycles determine all the changes that follicles go through and that lead up to ovulation.
Many follicles are recruited months before ovulation, but only one follicle will mature and develop completely and become dominant. The dominant follicle contains the egg that will be ovulated. However, most follicles never reach ovulation.
If we look into our ovaries there are several follicles at different stages of development at any given time. There will be very immature follicles preparing for the cycle in 5-6 months all the way to a mature follicle that will participate in this month’s cycle.
When the hormones trigger ovulation, the follicle releases the egg from the ovary to the Fallopian tube, where it can be fertilized. Interestingly, the ovaries and Fallopian tubes are not attached. Hormones induce the Fallopian tube cells to have cilia or hair-like structures on their surface which movement causes a flow carrying the egg from the ovary to the uterus. On top of this, smooth muscle activity increases as the result of the hormonal signals, muscle activity also participates in the transport (1,2).
When do you ovulate?
Traditionally it was said it was mid-cycle or day 14, but it is very rare that women ovulate on day 14 every cycle. In fact, most women do not ovulate on day 14. It is usual that women ovulate on days 12 to 16, or could be even later.
The moment ovulation occurs is defined by a complex hormone interaction that leads to the rise in Luteinizing hormone (LH) levels. The LH peak causes the follicle to rupture and the egg to be released to the Fallopian tube (3).
Ovulation occurs 22 – 33 hours after the LH rise and 12 – 24 hours after the LH peak. Why is this important? Ovulation will determine your most fertile days, which are the day of ovulation, the day after ovulation and around 5 days before ovulation. If you know when your LH rises and peaks you can determine the ovulation date and know when you are most fertile during your cycle.
How long does ovulation last?
Ovulation will happen around 12 -24 hours after the LH peak and the egg will survive up to 24 hours after ovulation. If the egg meets sperm it can be fertilized. If not, 24 hours later the egg will dissolve and your period will start around 2 weeks after.
Do you ovulate every cycle?
In general, we ovulate one egg every cycle. In exceptional cases, 2 eggs could be released and fertilized which could result in fraternal twins.
Some studies have shown healthy women not ovulating every cycle or having anovulatory cycles. But other studies have shown that it really depends on what level of progesterone is used to make the cut (4).
Some reasons for anovulatory cycles are that LH levels are not high enough to produce the follicle to rupture, or that estrogen levels are not high enough to induce the LH rise and peak.
What is certain is that ovulation is necessary to become pregnant and that if you are experiencing anovulatory cycles regularly you should see your doctor or Obgyn. Although, only your doctor or Obgyn can perform a vaginal ultrasound to actually know whether your cycle is ovulatory or not for sure. An indirect way to check whether you are ovulating or not, is by looking at your LH peaks and confirm ovulation with Progesterone tests (PdG). When these tests are positive in 96% of the cases you have ovulated (5).
How to know if you ovulated?
here are a few methods to determine whether or not you have ovulated.
PdG is the urine metabolite of progesterone. After ovulation, the follicle that surrounded the egg forms the corpus luteum. The corpus luteum releases progesterone. Progesterone levels will increase after ovulation. PdG test strips can detect the high levels of progesterone confirming ovulation.
– Blood test
Progesterone can also be tested in blood to confirm ovulation. Approximately 7 days after ovulation, a serum level of 5ng/ml or higher confirms ovulation. This blood test has to be timed correctly for it to be useful (6).
– Basal Body Temperature increase (BBT)
After ovulation, the corpus luteum begins producing progesterone, which produces a rise in body temperature of around 0.5 degrees Fahrenheit. For women charting their BBT very accurately, it can be a useful way of confirming ovulation. However, BBT charts can’t predict when ovulation will happen; they only confirm that it occurred after it has happened.
Read all about BBT and TTC here
– Transvaginal ultrasound
If an ultrasound is timed correctly (< 24 hours), a skilled clinician can observe the dominant follicle about to be ovulated or can identify the follicle rupture site after the egg has been released. With luck and good timing, it is even possible to see the follicle rupturing (7).
- Science Direct, . (2016). Oocyte transport. Oocyte Transport – an overview | ScienceDirect Topics.
- Natural Institues of Natural Sciences, . (2014). How fallopian tubes carry eggs unidirectionally. EurekAlert!
- Homburg, R. (2014). The mechanism of Ovulation: GLOWM. Global Library of Womens Medicine.
- Malcolm, C. E., & Cumming, D. C. (2003, August 1). Does anovulation exist in eumenorrheic women? Obstetrics & Gynecology.
- Ecochard, R., Leiva, R., Bouchard, T., Boehringer, H., Direito, A., Mariani, A., & Fehring, R. (2013, July 4). Use of urinary pregnanediol 3-glucuronide to confirm ovulation. Steroids.
- Leiva, R., Bouchard, T., Boehringer, H., Abulla, S., & Ecochard, R. (2015, June 22). Random serum progesterone threshold to confirm ovulation. Steroids.
- Reproductive Facts, . (2006). Ovulation detection. Reproductive Facts.