Fertility & Ovulation
How cycles, ovulation and fertility testing work, with the sources behind each point.
Cycle basics
- The menstrual cycle is typically 21 to 35 days long for most adults (in teens it can range 21-45 days); the average cycle length is around 28 days, and it is normal for cycle length to vary somewhat from month to month.Source: NICHD (NIH)
- The same NICHD overview also confirms the general 21-35 day range using the phrase 'for most women, it is 21 to 35 days,' matching NHS guidance that regular cycles anywhere from 21 to 35 days are considered normal.Source: NHS
- Ovulation is triggered by a surge in luteinizing hormone (LH), and release of the egg typically occurs about 36 hours after the start of that LH surge.Source: ASRM
- The luteal phase is the second half of the cycle, running from ovulation until the next period starts; NHS guidance describes this post-ovulation window as typically 10 to 16 days before the next period begins.Source: NHS
Ovulation signs
- Around the time of ovulation, vaginal/cervical secretions typically become thinner, clearer and more stretchy — often described as similar to raw egg white — and this is generally the most fertile-feeling type of mucus.Source: NHS
- In a large study cited by ASRM, pregnancy rates were highest (around 38%) when intercourse occurred on the day of peak (egg-white type) cervical mucus, compared with 15-20% on other fertile-window days, and cervical mucus changes predicted the day-specific chance of conception as well as or better than basal body temperature or urinary LH monitoring.Source: ASRM
- ASRM notes that ovulation predictor kits/devices that detect the urinary luteinizing hormone (LH) surge have real limitations: in one comparison study, LH-based and app-based predictors reached a maximum accuracy of only about 21% in predicting the exact day of ovulation, false-positive LH results occur in roughly 7% of cycles, and ovulation itself can occur any time within about 2 days after a positive LH test.Source: ASRM
- ASRM defines the fertile window as the 6-day interval ending on the day of ovulation (i.e., ovulation day plus the 5 days before it), with peak fertility in the 2 days before ovulation and the highest per-cycle pregnancy probability when intercourse occurs the day before ovulation.Source: ASRM
- It is common to feel mild one-sided lower-abdominal pain around ovulation, roughly 14 days before a period, often described as a dull ache or sharp sudden twinge; this ovulation pain (mittelschmerz) usually lasts from a few minutes up to 1-2 days and is generally not a cause for concern unless it is severe or persistent.Source: NHS
- In an average 28-day menstrual cycle, ovulation typically occurs about 14 days before the next period starts, but cycle length and the timing of ovulation can vary considerably between individuals and from month to month.Source: Mayo Clinic
- Having sex regularly from about 3 to 4 days before ovulation until roughly one day after ovulation improves the odds of conception, because sperm can survive in the female reproductive tract for about 3 to 5 days while the released egg itself can only be fertilized for about 12 to 24 hours.Source: Mayo Clinic
Timing & tips
- For couples trying to conceive, having sex every day or every other day during the 6-day fertile window gives the best chance of pregnancy, though daily sex is not required — sperm can live in the body for up to 5 days.Source: ACOG
- Sperm can live inside the female reproductive tract for about 3 to 5 days after sex; because of this, having sex regularly from 3-4 days before ovulation until one day after ovulation improves the odds of getting pregnant. Couples who can't manage daily sex are advised to aim for every 2 to 3 days a week starting soon after the end of the period.Source: Mayo Clinic
- ASRM's committee opinion states that intercourse every 1 to 2 days during the fertile window yields the highest pregnancy rates, though intercourse every 3 days produces nearly equivalent results; couples should not deliberately limit frequency.Source: ASRM
- The fertile window is best defined as the 6-day interval ending on the day of ovulation, with the highest chance of pregnancy when intercourse occurs within the 2 days before ovulation.Source: ASRM
- There is no evidence that coital position, female orgasm, or remaining horizontal (lying down) after intercourse improves conception chances — ASRM's patient fact sheet states research does not support these common beliefs.Source: ASRM
- Some common lubricants (including certain brands like Astroglide and KY Jelly, as well as saliva and olive oil) may impair sperm movement and viability, while alternatives such as Pre-Seed, mineral oil, or canola oil do not show this negative effect.Source: ASRM
- An NIH-funded study of 274 women trying to conceive found that women with the highest levels of alpha-amylase (a marker of the stress hormone system) had about a 12% lower chance of conceiving each cycle compared to those with the lowest levels, though a related stress hormone, cortisol, was not linked to reduced conception in the same study.Source: NICHD (NIH)
- ACOG notes that using fertility trackers and apps to time intercourse can create a sense of urgency around getting pregnant, and that many people find this information overwhelming and become fixated on doing everything 'just right,' which can add unnecessary stress to sex.Source: ACOG
- ASRM's committee opinion acknowledges that stress associated with trying to conceive can reduce sexual esteem and satisfaction and the frequency of intercourse, particularly when couples follow rigid ovulation-prediction schedules, and recommends that fertility-awareness methods be used to guide frequent intercourse rather than replace it.Source: ASRM
Educational reference only — not medical advice. Every fertility journey differs. Always consult your doctor or midwife.