Advice on ovulation prediction to determine the fertile window

Ovulation prediction can help determine the fertile window (the days on which conception is possible); this lasts from 5 days before ovulation until the day it occurs, as sperm survive in the female reproductive tract for this duration. Intercourse every 2 to 3 days is adequate during this time period to achieve pregnancy.

In discussing the normal fertile window, provide advice about how to predict ovulation. No single method of ovulation prediction is ideal; options include:

• calculating the day of ovulation from historical menstrual cycle data (if cycles are regular): ovulation is expected about 14 days before the last day of the cycle (eg for a 30-day cycle, ovulation is expected on day 16)
• measuring basal body temperature: detecting the 0.2 to 0.5°C rise in body temperature that occurs following ovulation
• assessing cervical mucus: texture becomes slippery several days before ovulation; see the Billings Ovulation Method
• measuring urinary luteinising hormone (LH) concentration: the most useful adjunct to menstrual cycle data; this detects an LH surge about 20 hours before ovulation.

Testing salivary composition is not reliable for ovulation prediction.

Fertility applications (apps) predict ovulation using historical menstrual cycle data, sometimes in combination with one or more other parameters. Apps are popular but generally unreliable, particularly those using historical cycle data alone.