Fertility basics
How conception works
Ovulation occurs roughly 12 to 16 days before your next period. The fertile window is the five days before ovulation plus the day itself — because sperm survive up to five days while the egg survives only 12 to 24 hours.
That asymmetry is why the days before ovulation matter more than the day after.
What counts as a normal cycle
Normal menstrual frequency is 24 to 38 days, under FIGO terminology. This replaced the older 21 to 35 day definition still widely quoted. Cycles are regular if the gap between your shortest and longest stays within about 7 to 9 days.
How long conception normally takes
Roughly one in five per month with everything working well. Most couples who conceive do so within six months; the large majority within a year.
Several months without success is normal.
When to seek help
12 months of trying if under 35. 6 months if 35 or over.
Sooner if: cycles are irregular or absent; known or suspected endometriosis or PCOS; previous pelvic infection or surgery; two or more miscarriages; either partner has a known concern; or you are 40 or over.
Both partners, together
Male factor is involved in a substantial proportion of cases and is typically symptomless. A semen analysis is quick, inexpensive and non-invasive, and should be among the first tests — not arranged after the female partner has been fully investigated.
The tests
Female: day 2 or 3 FSH and LH, AMH, prolactin, thyroid function. Pelvic ultrasound with antral follicle count. Tubal patency testing where indicated.
Male: semen analysis, repeated if abnormal since results vary substantially between samples.
Timing in the cycle matters for several female tests — a common reason results come back falsely normal.
One thing worth understanding early
AMH predicts how you would respond to stimulation. It does not predict whether you will have a baby. ESHRE (2026) makes both points as separate strong recommendations.
A low AMH with regular cycles is not a reason to panic, and it is routinely communicated as though it were a prognosis.
Things that matter less than you might think
Precise timing beyond covering the fertile window. Position or lying down afterwards. Ordinary stress.
One thing that does matter
Many standard lubricants impair sperm motility, as does saliva. Use a product labelled fertility-friendly if you use one.
Where to go next
Explore the guides on female fertility, male fertility, PCOS, endometriosis, IVF and recurrent miscarriage for detail on each.
Frequently Asked Questions
What are the basics of fertility?▾
Fertility is the capacity to conceive a child. It requires: regular ovulation in women, open fallopian tubes, a receptive uterine lining, and adequate sperm in men. The fertile window is 6 days per cycle — the 5 days before ovulation and ovulation day. Per-cycle natural conception rates range from ~25% in the mid-20s to ~5% at age 40 (ASRM 2023).
What tests check fertility?▾
For women: AMH blood test (ovarian reserve, any cycle day), Day 2–3 blood panel (FSH, LH, estradiol, prolactin, TSH), pelvic transvaginal ultrasound (antral follicle count, uterine cavity), and tubal patency test (HyCoSy or HSG). For men: semen analysis ×2 (4–6 weeks apart) — this identifies male factor in 40–50% of infertile couples.
When should I worry about not getting pregnant?▾
ASRM 2023: seek evaluation after 12 months of trying if under 35 with no risk factors, after 6 months if 35–39, and immediately at age 40+. Seek evaluation sooner if you have irregular periods, known PCOS or endometriosis, previous pelvic infections, two or more miscarriages, or a partner with known fertility issues.
What affects fertility the most?▾
For women, age is the single most important factor — egg quality declines significantly from the mid-30s. Other major factors: ovulation regularity, tubal patency, uterine health, and thyroid function. For men: sperm count, motility, morphology, DNA integrity, varicocele, and lifestyle factors (smoking, steroids, heat). Male factor contributes to 40–50% of all infertility.