Sex, Timing and the Fertility Myths That Refuse to Die

The honest picture, with numbers

The biology of timing is settled and narrower than most advice implies. ASRM's committee opinion on optimizing natural fertility defines the fertile window as the 6-day interval ending on the day of ovulation, with peak fecundability in the 2 days before ovulation. Conception is essentially impossible outside that window, because sperm survive several days in the reproductive tract and the egg survives a matter of hours.

What follows from that is less dramatic than the internet suggests. ASRM's recommendation is intercourse every 1 to 2 days during the fertile window for the highest pregnancy rates, while noting that results with intercourse 2 to 3 times a week are nearly equivalent. NICE NG257's version is simpler: intercourse every 2 to 3 days optimises the chance of pregnancy. Both are saying the same thing — regular sex across the cycle beats trying to hit one perfect day.

ASRM also gives the context number that matters: approximately 80% of couples conceive in the first 6 months of trying.

The myths, one at a time

"You have to lie with your legs up afterwards"

No. ASRM states there is no scientific basis for remaining supine after intercourse, and that sperm reach the fallopian tubes within about 15 minutes regardless of position. Get up whenever you like.

"Some positions work better"

No. ASRM states there is no evidence that coital position affects fecundability.

"Lubricant will ruin your chances"

Not according to the outcome data. Some water-based lubricants do inhibit sperm motility in laboratory conditions, which is where this belief comes from. But ASRM reports that lubricant use in couples attempting conception was not shown to affect cycle fecundability compared with non-use, and notes that mineral oil and hydroxyethylcellulose-based products raise no concerns. Painful sex is a much bigger obstacle to conception than lubricant is. NICE does flag vaginal lubricants among over-the-counter products clinicians should ask about, so mention what you use — but do not endure discomfort on the strength of a laboratory finding.

"Saving up sperm for the fertile days helps"

No. ASRM states that intercourse more frequently than every 1 to 2 days is not associated with lower fecundity, and that couples should not be advised to limit frequency when trying to conceive.

"Your temperature chart tells you when to have sex"

It cannot. Basal body temperature rises after ovulation, so a chart is retrospective by design. NICE goes further and recommends against using BBT charts to confirm ovulation, on the grounds that they do not reliably predict it.

"Ovulation is always day 14"

Only in a textbook 28-day cycle. NICE's own testing guidance builds this in: mid-luteal progesterone is taken on day 21 of a 28-day cycle, but later — for example day 28 of a 35-day cycle — where cycles are longer, and repeated weekly where they are irregular.

"Cut the coffee"

NICE states there is no consistent evidence of an association between caffeinated drinks — tea, coffee, energy drinks, colas — and fertility problems. ASRM's version is that moderate consumption of 1 to 2 cups a day has no adverse effect, while high intake above 5 cups a day is associated with decreased fertility. Somewhere between those two is your answer, and it is not zero.

"Just relax and it will happen"

This one deserves precision rather than dismissal. NICE's actual recommendation is that stress in either or both partners can affect the couple's relationship and is likely to reduce libido and frequency of intercourse, which can contribute to fertility problems. That is a mechanical pathway — less sex — not a mystical one. There is no NICE recommendation telling you that anxiety is preventing conception directly, because there is no guidance-grade evidence that would justify one. When someone tells you it will happen once you stop thinking about it, they are managing their own discomfort.

Does trying to time it actually help?

This is the part where the evidence is more interesting than the folklore. The 2023 Cochrane review of timed intercourse covered 7 randomised trials and 2,464 women:

• Urine ovulation tests versus intercourse without ovulation prediction: urinary ovulation detection probably increases the chance of live birth — risk ratio 1.36 (95% CI 1.02 to 1.81), one trial, 844 participants, moderate-quality evidence. Against a 16% baseline live birth rate, that suggests 16% to 28%. It probably also increases clinical or positive urine pregnancy tests, RR 1.28 (95% CI 1.09 to 1.50), four trials, 2,202 participants, moderate quality.
• Fertility awareness-based methods — temperature charting, cervical mucus monitoring, calendar apps — versus no ovulation prediction: uncertain. RR 0.95 (95% CI 0.76 to 1.20), two trials, 157 participants, low-quality evidence.
• Effect on stress: uncertain in both arms, on very low-quality evidence. Cochrane could not confirm or rule out an effect on stress, anxiety, depression or erectile dysfunction.

The authors' conclusion is careful and worth reproducing accurately: timed intercourse using urine ovulation tests probably improves live birth and pregnancy rates in women under 40 who have been trying for less than 12 months, compared with intercourse without ovulation prediction. That is a narrower claim than "track everything".

What to do next

1. Have sex every 2 to 3 days across the cycle. It covers the fertile window without requiring you to predict anything, and it is what NICE recommends.
2. If you want to add one tool, make it a urine LH test — that is the intervention with the best evidence behind it, and the benefit is clearest in the first year of trying.
3. Do not add a temperature chart to answer "am I ovulating". A correctly timed mid-luteal progesterone blood test answers that question properly; NICE recommends it even when cycles are regular.
4. Drop the rituals that have been tested and found not to matter: lying down afterwards, positions, avoiding lubricant, rationing sex.
5. Notice if timing is damaging the relationship. NICE's own recommendation runs through libido and frequency — if a schedule is reducing how often you have sex, it is working against you.

When to seek help

NICE recommends assessment of both partners after 1 year of unprotected vaginal intercourse, and referral at first presentation if the woman trying to conceive is 36 or over, or if either partner has a known or suspected cause. ACOG's thresholds are 12 months, 6 months if you are older than 35, and a conversation now if you are older than 40.

Go sooner if you have irregular or absent periods, pain during sex, or difficulty having intercourse at all. NICE recommends offering an initial consultation to discuss the options for attempting conception to anyone who is unable to, or would find it very difficult to, have vaginal intercourse — and it recommends that the setting should allow sensitive issues, including sexual abuse, to be discussed. That is a real pathway, and no one should be timing their cycle around sex that is painful or unwanted.