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Ovulation prediction: A tool for the couple trying to conceive

By Dr. Joe Massey, MD

Since few couples have intercourse every day, it is useful to know the best time to promote conception. A fertility app can estimate the “fertility window” based on your history of recent cycles. Basal temperature charting can help narrow down what to expect, but is out of vogue thanks to the widespread use of ovulation prediction tests.

Some facts about reproduction

The fertility window

Understanding some basic facts of reproduction can be helpful to understanding the rationale for ovulation prediction. We are trying to get sperm and egg together within a fertile window of time, which can last two to three days in any particular month. Sperm that have been ejaculated into the vagina are taken up quickly through the cervix, and some are transported directly to the tubes within minutes. The sperm can’t swim very fast, so small contractions of the wall of the uterus enhance sperm transport. Of the many millions of sperm that are in the vagina, only hundreds can be found in the fallopian tubes at any one time.

The timing does not have to be exact, because sperm can live for one or two days easily in the cervical mucus – there are even cases of pregnancy five days after the last sexual intercourse. The explanation for the longer window is that some of the sperm settle into little pockets of the cervix and happily wait their turn to travel to the uterine cavity and tubes. There they await the arrival of an egg. Once in the tubes, the two tiny cells find each other in the complex folds of the tube due to chemical signals from the egg. However, getting within five days is not our goal here – we want to get as close to the actual ovulation day as possible.

While it is true that a window of five days is possible for conception, the limiting factor is the fact that the egg is only viable for 24 hours. That is a rigid rule and is the reason we strive to pinpoint the day of ovulation.

How does ovulation work?

We know that the time of ovulation is reliably 14 days before a period.

The initial growth of a follicle in the ovary is in response to the pituitary hormone called follicle stimulating hormone, or FSH. As the dominant follicle in the ovary ripens and approaches maturity, a sudden surge of luteinizing hormone (LH) is released by the pituitary. There is very little LH present until mid-cycle.

This LH surge starts after midnight in most cases and as a result, the hormone can generally be detected in the urine the next day. The LH surge in urine alerts us that the peak is about to occur. Interestingly, the brief LH peak in blood occurs hours later than it appears in urine, and is actually responsible for triggering ovulation. After the LH surge, the process of final maturation of the eggs begins, leading to release in about 40 hours. Then the tube picks up an egg, and the sperm and egg are trying to meet.

Ovulation prediction

Basal body temperature charts

Basal body temperature (BBT) charts are mostly a way to see your ovulation history, since they only reveal when ovulation has already occurred. Generally, this is not helpful to predict the day of ovulation in the future. Further, ovulation prediction kits (OPKs) and fertility apps have made calendar prediction of the fertility window so easy that the BBT has lost its utility.

Ovulation prediction kits

OPKs, invented in the early 1980s, use very sensitive diagnostic reagents to detect the small amount of LH in the urine. Once the test is positive, don’t keep testing – ovulation is about to happen. LH may continue to show up in the urine for several days, but the first day of positivity is your signal to attempt conception. An exception is found in some PCOS patients who have chronically elevated LH. For them, the tests are confusing and not helpful.

Studies have shown that using testing methods enables accurate timing and improves chances to conceive in fertile couples. Options for these over-the-counter tests are single-use kits and monitoring devices that are useful for tracking multiple cycles. Generally, a morning urine sample is recommended, as the urine is concentrated in the morning. It’s best to follow the instructions in the kit to let you know the optimal day to try to conceive.

Fertility apps

Using an app to identify a window of possible fertile days can be helpful. When you log the beginning of your menstrual cycle, fertility apps attempt to predict, using inbuilt algorithms, when ovulation might occur.

Consumer advisory articles on the various apps verify that they all seem to be roughly equivalent in functionality.

What to do next after the ovulation prediction says “Go!”

Having pointed out that you do not need to always hit the day perfectly, we are doing our best to time ovulation. For some people, this is easy to do. If a menstruating person has 28- to 30-day cycles, their day of ovulation varies from the 14th to the 16th day. And if they are that regular, they may elect to have frequent intercourse during those days and forget about any tests.

Ovulation prediction is not meant to dictate your sex life. It can’t hurt to overdo intercourse. For example, if you have a positive surge on Thursday morning, you know that the ovulation will be on Thursday or Friday. It can’t hurt, and it might be ideal, if you had intercourse on Wednesday. Thursday night is clearly the most important time for intercourse. For that matter, depending on when the egg was released, maybe even Saturday could work; trying can’t hurt. Don’t worry about depleting the sperm supply. As long as the sperm count is normal, there are plenty of reserves of sperm.

The American Society for Reproductive Medicine (ASRM) has many articles available for further reading on this topic.


As a well-known pioneer in IVF, Dr. Joe Massey loves to share in the joy of helping build families. Dr. Massey’s achievements in fertility medicine include involvement in the first pregnancy in the world following assisted hatching in 1988 and in the world’s first pregnancy following intracytoplasmic sperm injection (ICSI) in 1993. He has led a number of clinical trials and co-authored many articles published in medical journals.

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