ACOG clinical fertility standards
ACOG and the American Society for Reproductive Medicine (ASRM) emphasize that the fertile window is defined as the 6-day interval ending on the day of ovulation.
Clinical pregnancy rates peak with intercourse occurring on the 2 days immediately preceding ovulation (approximately 25% to 30% per cycle in young, healthy couples).
ACOG recommends formal fertility evaluation for couples attempting conception for 12 months without success when the female partner is under 35, or after 6 months for women aged 35 and older.
Worked example: Ovulation timing
A patient with an LMP of November 10th and a 26-day cycle ovulates on cycle day 12 (November 22nd).
The prime conception window spans November 17th through November 22nd, with the highest probability on November 20th and 21st.
US ovulation inputs
Cycle Length
Typical cycle duration in days.
CALCULATOR QUESTIONS
ACOG fertile window & conception calculator questions
How does age affect the monthly chance of conceiving?
A healthy woman in her twenties has approximately a 25% chance of conceiving per cycle. By age 35, this rate is roughly 15% per cycle, and by age 40, it declines to approximately 5% per cycle.
What is basal body temperature (BBT) charting?
Progesterone released by the corpus luteum after ovulation causes a slight rise in waking body temperature (about 0.5°F to 1.0°F). Because this rise occurs after ovulation, BBT confirms ovulation occurred rather than predicting it in advance.