The luteal phase is characterised by the release of progesterone, which helps prepare the uterus for implantation by thickening the uterine wall and supports the early development of an embryo.
Traditionally, ovulation was believed to start in the middle of the cycle and as a result the luteal phase was also assumed to take up the whole of the second half of the cycle – but we now know this isn’t always the case. By understanding exactly when your body enters this crucial phase, and what happens to your progesterone level during it, you can greatly improve your chances of getting pregnant and avoid the prospect of a miscarriage.
A short luteal phase – an ovulation that occurs nine days or less before the subsequent onset of menstruation – is one of the most obvious signs of a luteal phase defect (LPD). Falling progesterone during the luteal phase may also be a sign. LPD has been implicated as a cause of irregular menstrual bleeding, infertility and recurrent miscarriage.
If you notice signs of LPD it is important to seek clinical advice and treatment.
When can you conceive?
The date of ovulation is key to understanding the luteal phase, therefore the ‘fertile window’ – those days on which you can conceive within any given cycle. The literature generally defines the fertile window as the five days before ovulation up to the two days after ovulation.
A fertile window study published in the British Medical Journal (BMJ) in 2000, found 2% of women to be in their fertile window by the fourth day of their cycle, and 17% by the seventh day.
For some women, however, this window will occur much later in their cycle. An estimated 30% of OvuSense users ovulate more than 65% of the way through a cycle, which is consistent with the fertile window study.
By definition, this ‘late ovulation’ group is also likely to have a short luteal phase and it’s perhaps no coincidence that 30% of couples struggle to conceive within 6 months.
How to detect ovulation
There are many different ways to test for ovulation, however, some come with limitations.
Blood tests, conducted by a GP, can tell you if the levels of your hormones are in the normal range for ovulation.
If you are found not to be ovulating, lifestyle changes may be necessary. Maintaining a healthy diet and weight, exercising regularly, limiting alcohol consumption and not smoking can dramatically improve your chances of conception.
However, such changes alone are limited in their success without understanding when you ovulate in each cycle, and being aware of any specific issues which may cause you to ovulate irregularly.
Other methods, such as urine-based Ovulation Predictor Kits (OPKs) can test urine for a surge in Luteinising Hormone (LH), which triggers ovulation. OPKs take readings at snapshots in time, and require 2-3 tests a day for 10-20 days in each cycle to provide meaningful results. This can make these tests impractical, expensive and stressful if you have an irregular cycle.
In addition, women with Polycystic Ovaries and/or Polycystic Ovarian Syndrome often have high levels of the LH in general. These OPKs can therefore show a positive result at times when they are not ovulating, and a resulting confusion over when to try and get pregnant and of the luteal phase itself.
Diminished Ovarian Reserve (DOR), another common ovulatory issue, can lead to similar confusion. As an LH peak doesn’t necessarily result in ovulation, and as ovulation generally takes place at a slower pace in the cycle, any predictions are unreliable.
Charting your basal body temperature (BBT) can be an effective method if you have regular ovulation and cycles of a consistent length. As progesterone is released the body, your temperature increases, and the literature shows a BBT rise of 0.3 degrees Celsius or more can indicate ovulation has occurred, but only after it’s happened.
So, BBT can be used to predict ovulation in your next cycle, but if you ovulate at a different time each month, or if you have a more erratic temperature pattern – which is common if you have an ovulatory issue – then it’s of little use. The same issue can arise with fertility tracking apps and other temperature-based fertility monitors.
Monitoring cervical mucous secretions can increase the effectiveness of other methods of monitoring, but this is not always practical or desirable for all women.
OvuSense real-time fertility monitor
OvuSense, a real-time fertility monitor takes a woman’s core body temperature every five minutes overnight using a vaginal sensor, similar in size to a tampon. Data is downloaded each morning providing a real-time graph of core temperature level.
Unlike BBT, core body temperature shows the direct effect of progesterone on the body and because of the accuracy of measurement, it allows for prediction of ovulation using the data within the current cycle, and then a confirmation of the date of ovulation.
Clinical studies have shown OvuSense gets this prediction right 96% of the time, and confirms the exact date with 99% accuracy.
So OvuSense can act like an OPK and BBT measurement, but with the benefit that it works for all women, regardless of ovulatory issues.
In addition, by showing core temperature in real-time, it can help show the relative level of progesterone throughout the whole cycle, and in particular, show if you might have LPD because of falling progesterone in the luteal phase or a short luteal phase.
Our review of the literature and results so far with OvuSense show that putting women back in control of their fertility through a deeper understanding of their cycles can double their chances of successful pregnancy compared with other methods.
By Robert Milnes, CEO for OvuSense and Kate Davies, Independent Fertility Nurse
– See www.ovusense.com for more information