6 fertile days per cycle
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
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.
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.
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
- cervical softness, position,
- consistency of the cervix,
- increase in mucus and saliva electrolyte levels,
- crystallization of salts in mucus and saliva samples.
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
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.
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.
So when can I get pregnant?
- 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.