When is a woman the most fertile?

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The probability to get pregnant can be five times higher 2 days before ovulation than on the day of ovulation. Women are more beautiful than usual on these days! Of course, this is not the most reliable way to detect the most fertile days of the cycle but, luckily, there are other methods. The selection ranges from free fertility awareness to high-end devices that detect various physiological and hormonal changes. Before we dive into those, let’s get a few things straight.

6 fertile days per cycle

You can get pregnant only five days before ovulation or on the day of ovulation. It seems easy, but the human ovulation and fertile period is hidden. In a 1995 study, researchers asked 221 women who wanted to have children to record the days of unprotected intercourse. The researchers wanted to know the actual length of the so-called fertile window. They determined the exact day of ovulation from urine samples based on the hormones estrogen and progesterone. A total of 629 cycles were examined, during which 129 babies were born from 192 pregnancies. All conceptions occurred five days before or on the day of ovulation. Since then, we know that the fertile window is 6 days. They also examined the cycles where only one sexual act occurred during the 6-day fertile period. Out of 629, they found 129 such cycles. Then they estimated the chance of conception for the 6 fertile days. The probability of conception for each day with respect to the day of ovulation (day 0) was the following. The researchers included both clinical pregnancies and early losses of pregnancies here:
single day conception rate raw
The probability of actual conception on the 6 fertile days, involving mostly 26-35 year-old women.

This 1995 study clearly showed that sperm can survive in a woman’s body for up to five days after intercourse. Therefore, including the day of ovulation, there are 6 fertile days in each cycle when the egg can be fertilized.

The most fertile day

Twelve years later in a 2007 study, it turned out that the fertility peak is 2 days before ovulation and the probability of conception is very low on the day of ovulation. The researchers asked 728 couples to record the days of unprotected intercourse. Unfortunately, in this 2007 study, they examined the most fertile day with basal body temperature test. This does not show the exact day of ovulation, because you can only estimate it from temperature increase following ovulation. A urine test would have been better, but it would have cost much more. Nevertheless, the researchers were able to examine 5390 cycles and 434 pregnancies. Let’s see the results! The figure is a bit blurred, but the 6-day fertility window is outlined. In addition, the most productive day is clearly visible. The probability of conception for each day with respect to the day of ovulation (day 0) was the following. The researchers included only clinical pregnancies here:
single day conception rate 2007
The probability of conception on the 6 fertile days relative to the estimated day of ovulation involving 19-26 and 35-39 yearl-old women.

The probability to get pregnant is about 3-5 times higher 2 days before ovulation than on the day of ovulation depending on the age group. 

Live births

In the same 1999 study researchers also discovered that the egg ages until fertilization if intercourse occurs on the day of ovulation. This is why the chance of loss of pregnancy is higher for fetuses conceived on the day of ovulation. 

They wanted to know if old sperm would produce damaged embryos and would lead to pregnancy loss with higher probability. They looked at the 199 pregnancies and the most recent instance of intercourse before ovulation. They found the pattern of intercourse in relation to ovulation was similar overall, but there was:

  • higher probability of giving live births if last intercourse was 1 or 2 days before ovulation, and
  • higher probability of pregnancy losses if last intercourse was on the day of ovulation or 3, 4, 5 days before ovulation. 
Frequency Distribution of Live Births and Pregnancy Losses, According to the Time of the Most Recent Instance of Sexual Intercourse before Ovulation during the Cycle when Conception Occurred

Consequently old sperm and old egg may produce damaged embryos and may lead to pregnancy loss with higher probability. The egg gets old in 12 hours. The intercourse on the day of ovulation may not be ideal for conception because it takes time for the sperm to reach the egg in the fallopian tube.

The signs of fertility

If we understand what hormonal processes are going on in our body and pay attention to the signs that accompany them, we can better guess the fertility window and the  day of ovulation. As a first step, estrogen levels in the body begin to rise, and in parallel, the salinity of body fluids (level of electrolytes) increases. Then you should pay attention to the following:
  1. cervical softness, position,
  2. consistency of the cervix,
  3. increase in mucus and saliva electrolyte levels,
  4. crystallization of salts in mucus and saliva samples.
These methods including the fertile saliva fern pattern can indicate 3-4 days earlier that our body has begun to prepare for ovulation. In addition, there are less measurable signs such as a more attractive appearance, higher sexual desire, and e.g. greater sensitivity to odors.
Ovulation, menstrual cycle, follicular phase, luteal phase, sharp spike in levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), resulting from the peak of estrogen levels

As a second step, the pituitary gland releases large amounts of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) into the bloodstream. As a result, ovulation may occur 1 to 1.5 days later. LH can be detected in the urine approx. 6 hours later. So the LH can predict ovulation approx. 1 day in advance.

As a third step, the enlarged dominant follicle shrinks in size and develops a corpus luteum that produces progesteron. Estrogen production drops. The womb prepares for implantation. The size change of the follicle is clearly visible by ultrasound examination. Therefore, clinics examine the dominant follicle with ultrasound on a daily basis, it is clear from this whether ovulation has occurred.

Cycle without ovulation?

Sometimes the first two steps take place, but ovulation does not occur. This is called anovulatory cycle and has no fertility window. The frequency of ovulation decreases with age.

However, two ovulations are also possible in one cycle. This occurs in 1-2% of cases, but both eggs are not always fertilized. Just think of how rarely do we meet fratenal twins.

Home ovulation tests

Regular cycles

With regular cycles, body temperature or urine tests can work great. These products save changes in urinary LH by approx. 1 day before ovulation or changes in basal body temperature approx. 1 day after ovulation. The data is collected for 3 months by a mobile application that comes with the product. Then it can calculate for regular cycles when the fertile phase begins. This, in turn, means that the most fertile day is not indicated by actual hormone changes, but by data measured in the past. If there is a change in the cycle, the prediction may be wrong.

Irregular cycles

In case of irregular cycles, you have to rely on the body’s signals or on more expensive tests that can detect the rise in the estrogen level (or the fall in FSH) a few days before ovulation. Many women have irregular cycles (about 1/3), which also depends on age, health, lifestyle and body weight.

More and more people (even with regular cycles) learn the natural signs of their fertility. The Babyndex application complements this, it provides assistance with the saliva ovulation test. It recognizes the crystals in dry saliva samples that appear during the fertile period.

Maybe Baby ovulation microscope
Using an ovulation microscope, fern-like patterns, crystals in saliva can be observed. Many women can determine fertile days based on this. Babyndex is the first application that can recognize fertile saliva fern patterns. At the current stage of development, it shows the probability of the occurrence of crystals, but it will soon indicate the peak of fertility in a personalized way. According to a study by Harvard Medical School, the ovulation saliva test can predict ovulation with 99% accuracy by image recognition of crystals. The Babyndex application already helps more and more women in identifying the most fertile saliva fern pattern.

So when can I get pregnant?

When the body begins to prepare for ovulation, it is possible to get pregnant. The peak of fertility is two days before ovulation, but the exact day cannot be known in advance. In fact, it may be omitted. To conceive you need a mature egg. Since the cell released from the ovary can be fertilzed for approx. 12 hours, while the sperm can wait for 3-5 days, good timing is needed for success. Changes in body fluids indicate fertility first, e.g. during the fertile phase saliva ferning patterns change. The Babyndex application recognizes these patterns. In fact, not only women are prettier at the peak of fertility, but also their crystals.
Microscope
If you have any further questions about fertility, write to us at hello@babyndex.eu. If you have any concerns about your health, it is recommended to consult a doctor as soon as possible in order to get a clearer picture. Photos from Pixabay.com, Vecteezy.com and Wikipedia.com. References
  • Timing of Sexual Intercourse in Relation to Ovulation — Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the BabyAllen J. Wilcox, M.D., Ph.D., Clarice R. Weinberg, Ph.D. and Donna D. Baird, Ph.D., December 7, 1995, N Engl J Med 1995; 333:1517-1521, https://www.nejm.org/doi/full/10.1056/nejm199512073332301
  • Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation, D.B. Dunson, D.D. Baird, A.J. Wilcox, C.R. Weinberg, Human Reproduction, Volume 14, Issue 7, 1 July 1999, Pages 1835–1839, https://doi.org/10.1093/humrep/14.7.1835
  • Effects of Sexual Intercourse Patterns in Time to Pregnancy Studies, Joseph B. Stanford, David B. Dunson, American Journal of Epidemiology, Volume 165, Issue 9, 1 May 2007, Pages 1088–1095, https://doi.org/10.1093/aje/kwk111
  • An inexpensive smartphone-based device for point-of-care ovulation testing Vaishnavi Potluri, Preethi Sangeetha Kathiresan, Hemanth Kandula, Prudhvi Thirumalaraju, Manoj Kumar Kanakasabapathy, Sandeep Kota Sai Pavan, Divyank Yarravarapu, Anand Soundararajan, Karthik Baskar, Raghav Gupta, Neeraj Gudipati John C. Petrozza and Hadi Shafiee, PMC 2019 Dec 18. Lab Chip. 2018 Dec 18; 19(1): 59–67.