When a couple decides to try to conceive, advice pours in from every direction: "put your legs up after sex," "switch to boxer shorts," "morning is better." But what does science actually confirm? We examined 6 popular fertility myths and analyzed each one against studies published in peer-reviewed journals. Spoiler: reality is simpler — and more reassuring — than the folklore.
Myth 1: sexual position determines your chances of getting pregnant
Verdict: Myth.
The idea of lying with your legs in the air after sex to "help the sperm" is probably the most repeated TTC advice. The problem is that no randomized controlled trial has demonstrated that specific positions during or after intercourse increase pregnancy rates. Biology here is on your side: within less than 15 seconds of ejaculation, the highest-motility sperm have already reached the cervical mucus, regardless of gravity. The cervix acts as a natural sperm reservoir, and this process begins almost immediately. No post-coital position — whether elevating the hips, using a pillow, or lying still for 30 minutes — has been validated in controlled studies as increasing pregnancy rates. That energy is better invested in knowing the right days of your cycle.
Myth 2: lubricants do not affect sperm
Verdict: True — and it deserves attention.
This is the most consequential myth on the list. A 2014 study published in the Journal of Assisted Reproduction and Genetics tested the effects of common vaginal lubricants — including KY Jelly, Astroglide, and oil-based lubricants — on sperm motility, viability, and DNA fragmentation.1 The results were clear: several commercial products significantly reduced sperm motility in vitro. Lubricants with very low osmolality or acidic pH create a hostile environment for sperm. The good news: there are products specifically formulated for TTC couples — such as Pre-Seed and some iso-osmolar gels — that do not compromise sperm function. If the couple uses lubricant, checking for a "sperm-friendly" label is a simple step with real impact.
Myth 3: boxer shorts improve male fertility
Verdict: Partially true — but the real effect is small.
The logic is biological: the testes need a temperature roughly 2 to 4 degrees Celsius below body temperature to produce sperm efficiently. Tighter underwear would draw the testes closer to the body, slightly raising scrotal temperature. But population studies do not support this effect in practice. A study following 252 men in couples with conception difficulty found no significant association between underwear type and semen quality, including motility and sperm morphology.2 Prolonged, intense heat sources — daily sauna sessions longer than 30 minutes, a laptop on the lap for hours, working in very hot environments — have more robust evidence of negative impact than underwear choice. Switching underwear on its own probably will not move the needle.
Myth 4: morning sex increases your chances of getting pregnant
Verdict: Partially true — but timing within the cycle matters far more than time of day.
There is a biological basis for this advice. A 2020 Japanese study published in Systems Biology in Reproductive Medicine compared semen samples collected in the morning and at night from the same group of 40 men. Morning samples showed slightly higher total motile sperm counts.3 This likely relates to higher testosterone levels in the morning. That said, the difference is modest and clinically irrelevant for most couples with normal fertility. What truly determines conception probability is being in the fertile window — the 6 days around ovulation. A couple having sex at 11 p.m. on the right cycle day has a far higher conception probability than a couple having sex at 7 a.m. outside the fertile window.
Fact 1: the fertile window is short and starts before ovulation
This is the finding that most changes a TTC couple's strategy. Levvi tracks your cycle precisely because a landmark study in the New England Journal of Medicine followed 221 healthy women trying to conceive across 625 menstrual cycles. The conclusion was precise: conception only occurred when intercourse happened within the 6 days ending on ovulation day.4 The egg survives 12 to 24 hours after ovulation; sperm can survive up to 5 days in favorable cervical mucus. Sex in the days before ovulation is just as effective as on the exact day. Levvi automatically identifies this fertile window from your logged cycles, showing the highest-probability days based on your individual average cycle length.
Fact 2: frequency during the fertile window matters
There is a frequent misconception that "saving" sperm for several days increases the count and improves the chances. Science points in the opposite direction. A reproductive epidemiology study found that couples with higher sexual frequency during the fertile window — daily or every 2 days — had shorter time to conception compared with couples who had sex only once per cycle.5 The study of 252 men also showed that ejaculatory frequency was positively correlated with progressive sperm motility.2 Most reproduction specialists recommend sex every 1 to 2 days during the 5 days before estimated ovulation. This maintains adequate sperm count and ensures coverage even if ovulation varies slightly from the cycle prediction.
What actually moves the needle
The science is clear about what truly matters for conception: being in the right fertile window and eliminating the few factors with solid evidence of negative impact. Stop using conventional lubricants and switch to iso-osmolar versions designed for conception. Maintain adequate sexual frequency during fertile days. Avoid prolonged, intense heat sources for the testes — not necessarily the underwear, but a daily sauna or laptop on the lap for hours. Everything else — position, time of day, elevating the hips — belongs to folklore, not physiology. Levvi automatically calculates the fertile window based on your logged cycles and shows the highest-probability days for conception, so the couple can focus energy where it truly makes a difference.