When it comes to getting pregnant through intercourse, timing is extremely important. Dr. Barry Witt, Reproductive Endocrinologist at Illume Fertility, walks us through the nuances, and breaks down how to best time intercourse when trying to conceive (TTC).
Understanding the Menstrual Cycle
The first thing you’ll need to understand is how the menstrual cycle works. The menstrual cycle begins with the onset of the period at which point the follicles in the ovary (where the eggs are) are small and estrogen levels are low. Over the course of 2 weeks (this can vary significantly) usually one follicle grows and secretes higher amounts of estrogen, so that when the follicle is large and ready to ovulate, an LH surge occurs which results in ovulation about 36 to 40 hours later. Ovulation is the process whereby an egg is released from the ovarian follicle. After ovulation, the egg enters the fallopian tube where it can be fertilized by sperm that has arrived there following intercourse. Sperm deposited at the cervix during intercourse enters the cervical mucus and then swims up to the fallopian tube so that fertilization can occur and ultimately pregnancy can ensue. If the sperm isn’t there because intercourse was not timed correctly, then pregnancy won’t happen, so timing intercourse is necessary. While it may seem like timing is precise here, the concept known as the “fertile window” makes things slightly more complicated.
The Fertile Window
The fertile window takes place prior to, during and shortly after the release of an egg (ovulation). During a single menstrual cycle, this is when a woman is most fertile and happens between around 6 days prior to and up to and including the day after ovulation. The fertile window is a consequence of the time that the sperm remains viable in the female reproductive tract (thought to be about 4 to 5 days) and the time that an egg is most viable (approximately 24 hours). Thus, the earliest time that intercourse would result in pregnancy is about 6 days prior to ovulation and the latest would be one day after. The greatest chance of conception occurs with intercourse 1 to 2 days prior to the actual ovulation, but pregnancy may be achieved at any point within the fertile window.
Tracking and Identifying Ovulation
Accurate prediction of ovulation can be challenging. Since the chance of getting pregnant increases with the frequency of intercourse during the fertile window, increasing the frequency of intercourse beginning soon after the end of the menses and continuing to ovulation is recommended. The chance of pregnancy is highest when intercourse occurs every 1 to 2 days. Ovulation detection devices are most useful for those couples that have infrequent intercourse (like once or twice a month), in which case these devices may reduce the time to conception.
There are several methods for estimating the time of maximum fertility (when to best time intercourse) during a menstrual cycle. It makes sense that accurate timing would be helpful since intercourse is most likely to result in a pregnancy when it occurs within the 3-day interval ending on the day of ovulation. But the length of the menstrual cycle can vary from month to month which makes it difficult to pinpoint the day of ovulation.
There is, however, no substantial evidence that monitoring for ovulation significantly increases the chance of pregnancy in the cycle when compared to just having frequent intercourse. There is, however, a common perception that the timing of intercourse is crucial, thus prompting many women to use technology to track her cycle and time intercourse. Ovulation detection devices, including kits for monitoring urinary luteinizing hormone (LH) and electronic monitors, are promoted as being helpful to determine the fertile window (ovulation usually occurs anytime within 2 days of a detected LH surge). Despite the technology, studies show that about 7% of these detected surges are false positives that do not actually reflect a true LH surge. Some of these devices are expensive and have not demonstrated ovulation prediction any better than cervical mucus tracking.
One easy and inexpensive way to find the fertile window is to use a menstrual calendar by taking the shortest cycle length and the longest cycle length and subtracting 14 (menses typically occurs about 14 days after ovulation if pregnancy doesn’t occur). So, for instance, if the cycle is anywhere between 25 and 30 days, ovulation is likely between day 11 and 16 (where day 1 is the first day of menstrual flow). Again, the ‘fertile window’ is best defined as the 6-days prior to and including the day of ovulation.
Women may also monitor their cycles by tracking changes in cervical mucus (it becomes clear and slippery like egg whites for several days prior to ovulation) with the highest chance of pregnancy being when intercourse occurs on the day of the peak mucus. This appears to predict the time of peak fertility better than just using the menstrual cycle calendar alone.
So, the simplest and least expensive method for timing intercourse to conceive is to track the length of the menstrual cycle, determine the likely fertile window based on the cycle length, monitor cervical mucus starting with the end of the menstrual period, and have intercourse every one to two days until the mucus is no longer watery.
Some women still choose to use other tools to help with timing intercourse. Ovulation trackers or apps may incorporate menstrual cycle information, cervical mucus amount and quality, symptoms such as breast tenderness, bloating, and possible cramping or pain in the side.
Ovulation test strips work by measuring levels of luteinizing hormone (LH) in the urine. A rise in LH signals the ovary to release an egg so when levels reach a certain threshold, it’s safe to assume that ovulation will occur within the next 12 to 36 hours.
There are some more sophisticated monitors that measure skin temperature, heart rate variability, breathing rate, resting pulsing rate, and skin perfusion, and may even use an artificial intelligence algorithm to determine the fertile window.
Others look at circadian rhythm core body temperature patterns using a vaginal device that provides 24/7 continuous core body temperature monitoring. Users are notified when core body temperature readings are consistent with the fertile window, several days before the actual LH surge occurs.
Fertility apps (or cycle tracking in general) are not helpful for women with very irregular or long menstrual cycles (like women with polycystic ovarian syndrome or PCOS) because in many of those women, ovulation either isn’t occurring, or is happening very infrequently. In those cases, seeking out medical assistance is warranted because medications to induce ovulation are likely necessary.
Menstrual calendar apps used for determining the day of ovulation have been demonstrated to have a maximal probability of being correct of about 20%. Urinary LH kits are more accurate with an 80% chance of detecting ovulation with 5 days of testing, and a 95% chance with 10 days of testing, but they do have a 7% false positive rate (detect a surge that isn’t there). Accuracy of the more sophisticated technologies using body signs like skin or body temperature and pulse rates is suggested to be approximately 90% for detecting the fertile window.
Since the fertile window is relatively long (about 6 days each cycle), It isn’t necessary to have intercourse every day and there is no specific moment when sex must be timed urgently. The low-tech methods of timing, like the menstrual calendar and cervical mucus monitoring are probably adequate for most couples, but some will choose to use higher tech methods in order to feel they are taking additional control over their fertility.
It is normal to not get pregnant right away but more than half of couples will conceive within 6 months of trying. For those who are under 35, trying up to 1 year is reasonable before seeking medical help. For those over 35, 6 months is adequate and seeking help from a reproductive endocrinologist at that point is recommended.