Fertility Basics: Your Complete Starting Guide
Fertility is the natural capacity to conceive a child. For most people it is assumed until it becomes difficult — at which point the lack of basic knowledge becomes an obstacle. This guide covers how conception works, what affects fertility in both partners, which tests matter, and what evidence-based steps genuinely improve your chances.
How Conception Works
Natural conception requires a precise sequence of events within a narrow window.
Step 1 — Ovulation. One dominant follicle matures and releases an egg, triggered by an LH surge 24–36 hours before release. The egg survives only 12–24 hours after ovulation.
Step 2 — The Fertile Window. Sperm survive in the female tract for 3–5 days, creating a fertile window of 6 days per cycle — the 5 days before ovulation plus ovulation day. The two most fertile days are immediately before ovulation.
Step 3 — Fertilisation. Of hundreds of millions of sperm, only a few hundred reach the fallopian tubes. One sperm penetrates the zona pellucida and fuses with the egg, creating a zygote.
Step 4 — Embryo Development. The fertilised egg divides while travelling to the uterus. By Day 5–6 it has developed into a blastocyst of ~100–200 cells.
Step 5 — Implantation. The blastocyst attaches to the endometrium (uterine lining) 6–10 days after fertilisation. Successful implantation triggers hCG production — the pregnancy hormone detected by tests.
Per-cycle natural conception rates — ASRM 2023:
| Age | Per-Cycle Rate | 12-Month Cumulative |
|---|---|---|
| 20–24 | 25–30% | ~95% |
| 25–29 | 22–28% | ~90% |
| 30–34 | 18–22% | ~85% |
| 35–37 | 12–18% | ~75% |
| 38–40 | 8–12% | ~60% |
| 41–43 | 4–8% | ~35% |
| 44+ | 1–4% | ~15% |
What Affects Female Fertility
Age is the single most important factor. A woman is born with all the eggs she will ever have. More critically, egg quality (chromosomal competence) declines with age — from ~25% abnormal eggs at age 30 to ~75% at age 40. Per-cycle success falls because most eggs at older ages cannot develop into viable pregnancies.
Ovarian reserve — measured by AMH blood test and antral follicle count (AFC) ultrasound — reflects egg quantity. Low AMH means fewer eggs for stimulation. It does not directly measure quality, but quantity and quality tend to decline together.
Ovulation regularity — regular cycles (21–35 days, consistent month to month) indicate regular ovulation. Irregular or absent cycles suggest ovulatory dysfunction, found in 25–30% of infertile women. PCOS is the most common cause.
Fallopian tube patency — tubes must be open and functional. Tubal damage from prior infection (chlamydia is the leading cause), endometriosis, or surgery causes 25–35% of female infertility. Blocked tubes produce no symptoms — testing is required.
Uterine health — polyps, submucous fibroids, intrauterine adhesions (Asherman's syndrome), and a uterine septum impair implantation. Most are correctable by hysteroscopy.
Hormonal health — thyroid disorders, elevated prolactin, and insulin resistance (PCOS) disrupt the hormonal axis driving ovulation.
What Affects Male Fertility
Male factor contributes to 40–50% of all infertility — equal to female factor, yet frequently under-investigated.
WHO 2021 reference values:
| Parameter | Lower Reference Limit |
|---|---|
| Concentration | ≥16 million/mL |
| Total motility | ≥42% |
| Progressive motility | ≥30% |
| Normal morphology (Kruger) | ≥4% |
Key causes: Varicocele (dilated scrotal veins — present in 35% of infertile men, most common correctable cause), genetic disorders (Klinefelter syndrome, Y-chromosome microdeletions), hormonal disorders (hypogonadotropic hypogonadism), lifestyle factors (smoking reduces count 15–20%; anabolic steroids completely suppress sperm within 2–3 months; heat exposure from laptops/hot baths raises scrotal temperature above the 33–34°C required for spermatogenesis).
Essential Fertility Tests
For women:
- AMH (any day of cycle): ovarian reserve
- Day 2–3 blood panel: FSH, LH, estradiol, prolactin, TSH
- Pelvic ultrasound: antral follicle count, uterine structure
- Tubal assessment: HyCoSy (ultrasound) or HSG (X-ray)
For men:
- Semen analysis ×2 (4–6 weeks apart): only way to assess sperm — no symptoms reliably predict it
- Sperm DNA fragmentation: not part of standard analysis; important for recurrent miscarriage or failed IVF
When to Seek Help — ASRM 2023 & ESHRE 2024
| Situation | When |
|---|---|
| Woman under 35, no risk factors | After 12 months trying |
| Woman 35–39 | After 6 months |
| Woman 40+ | Immediately — seek evaluation before or at start |
| Irregular periods, known PCOS or endometriosis | Before trying |
| Previous pelvic infection or STI | Before trying — check tubes first |
| Two or more miscarriages | Immediately |
| Known male factor | From the start |
Evidence-Based Steps to Optimise Fertility Now
1. Track ovulation with LH test kits. Start testing Day 10 of a 28-day cycle. Positive = ovulation in 24–36 hours → have intercourse that day and the next.
2. Start folic acid 400–800mcg daily. Ideally 3 months before trying. Reduces neural tube defect risk by 70% (ACOG 2020). The neural tube forms before most women know they are pregnant.
3. Both partners quit smoking. Halves female fertility and reduces sperm count/quality 15–20%. Highest single-impact lifestyle change. Effect on sperm visible after 3 months.
4. Correct Vitamin D deficiency. Deficiency (<20 ng/mL) significantly reduces IVF and natural conception rates. Most Indians are deficient — a simple blood test identifies this.
5. Reach a healthy weight. BMI <18.5 or >27 both impair fertility. In overweight women with PCOS, 5% weight reduction restores ovulation in 55% of cases.
6. Reduce scrotal heat (men). Laptops off the lap, loose cotton underwear, no hot baths or saunas. Full effect visible in semen analysis 3 months after change.
7. Stop anabolic steroids (men). These completely suppress sperm production within 2–3 months. Recovery takes 6–24 months after stopping.
Reference: ASRM Practice Committee — Optimisation of Reproductive Fitness, 2022. ESHRE Good Practice Recommendations — Optimising Natural Fertility, 2021 (updated 2024). ACOG Practice Bulletin No. 194 — Polycystic Ovary Syndrome, 2018 (reaffirmed 2023). WHO Laboratory Manual for Semen Analysis, 6th edition, 2021.
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.