Understanding your cycle.
A comprehensive evidence-based guide to women's cycles and hormones for conception. Understanding your cycle is foundational to making informed choices about your fertility journey, whether you're actively trying to conceive or simply wanting to know your body better.
The menstrual cycle: an overview
The menstrual cycle is the body’s periodic preparation for ovulation and potential pregnancy, regulated by hormones secreted from the hypothalamus, pituitary gland, and ovaries. According to the International Federation of Gynecology and Obstetrics (FIGO), normal menstrual cycles should have consistent frequency, regularity, duration, and volume of flow.
The four phases
Day 1 of the cycle is defined as the first day of menstrual bleeding. The typical volume of blood lost is approximately 30 mL. The decline in progesterone and oestrogen at the end of the previous luteal phase triggers the shedding of the endometrium.
This phase begins on day 1 and ends with ovulation. Follicle-stimulating hormone (FSH) promotes the maturation of ovarian follicles. Between days 5 and 7, follicle selection occurs. This phase ranges from 14 to 21 days and represents the most variable portion of the cycle.
When oestradiol reaches a threshold level (greater than 200 pg/ml for approximately 50 hours), it triggers the LH surge. The LH surge precedes ovulation by 35-44 hours. The released egg remains viable for only 12-24 hours after ovulation.
Following ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone. This phase is relatively consistent, typically lasting 14 days. Progesterone prepares the endometrium for potential implantation.
The same four phases as the cards above, drawn as one ring. This is a typical 28-day cycle, not a prediction about yours: the follicular phase is the part that stretches or shortens, which is why ovulation does not land on the same day for everyone.
Where ovulation actually lands
The follicular phase ends at ovulation, so its length is where ovulation lands. Across more than 600,000 cycles it averaged 16.9 days, and the 95% confidence interval ran from 10 to 30 days. Day 14 is the middle of a textbook cycle, not the middle of most real ones.
Bull et al., npj Digital Medicine, 2019 · 612,613 cycles from 124,648 women
Important: cycle variability
Key reproductive hormones
Understanding the hormones that regulate your menstrual cycle helps you interpret your body’s signals and make sense of fertility tracking methods. Each hormone plays a specific role in the intricate dance of conception.
This shows a typical pattern of the four main reproductive hormones. Tap any hormone name to learn more.
Tap the swatch to show or hide a curve. Tap the name to learn more.
This is an idealised pattern for educational purposes. Your actual levels will vary. Cycle length and hormone timing differ from person to person.
A typical 28-day cycle. Tap a hormone to read what it does, or its colour to hide the curve. AMH is not shown because, unlike these four, it stays broadly steady across the cycle.
Where these hormones come from
Each organ answers the one above it, and the answer travels back up. For most of the month rising oestrogen tells the pituitary to ease off, which is why FSH falls once one follicle takes the lead and the rest regress. Just before ovulation the same signal flips: oestrogen held high enough for long enough triggers the LH surge instead of damping it. After ovulation, progesterone from the corpus luteum holds the whole loop quiet until it falls away and the next cycle begins.
Oestrogen (Oestradiol)
The predominant oestrogen in women of reproductive age
- Produced by the ovaries during the early stages of the menstrual cycle
- Essential for the functioning of the uterus, including growth and maintenance of the endometrial lining
- During the late follicular phase, rising oestradiol levels cause cervical mucus to become clear, copious, and elastic
- Cervical mucus can increase up to 30-fold compared to the early follicular phase
- Creates a sperm-friendly environment that enhances chances of conception
Progesterone
Often called "the pregnancy hormone"
- Secreted by the corpus luteum after ovulation
- Plays a vital role in preparing the endometrium for implantation
- Triggers the lining to thicken, promotes capillary growth, and increases blood flow
- If implantation occurs, hCG from the fertilised egg maintains progesterone production
- Low progesterone levels are associated with difficulty conceiving and higher risk of miscarriage
Luteinising Hormone (LH)
The ovulation trigger
- Glycoprotein hormone produced by the pituitary gland
- Detection of the LH surge in urine is the most accessible method for predicting ovulation
- Mean time from positive urinary LH test to follicular rupture is 20 ± 3 hours
- The LH surge primarily occurs between midnight and early morning (85% between 00:00 and 08:00)
- Peak serum LH levels occur 10-12 hours before ovulation
Follicle-Stimulating Hormone (FSH)
The follicle developer
- Promotes the development and maturation of ovarian follicles during the follicular phase
- As the dominant follicle grows and produces more oestrogen, negative feedback reduces FSH levels
- This reduction causes non-dominant follicles to regress
- FSH levels can indicate ovarian reserve when tested early in the cycle
Anti-Müllerian Hormone (AMH)
The ovarian reserve marker
- Produced by granulosa cells in small, growing follicles
- Serves as a marker for ovarian reserve (remaining egg supply)
- Unlike other reproductive hormones, AMH levels remain relatively stable throughout the cycle
- Valuable for predicting response to controlled ovarian stimulation
- Important: AMH indicates egg quantity but not quality. Age remains the strongest predictor of egg quality.
The fertile window and conception timing
Defining the fertile window
The fertile window is the period during which intercourse can result in pregnancy, comprising the five days before ovulation, the day of ovulation, and potentially one day after. This six-day window is determined by:
Up to 5 days in fertile cervical mucus
12-24 hours after ovulation
Probability of conception by day
Variability and unpredictability
Women with shorter cycles ovulate earlier. One-third reach their fertile window by the end of the first week.
Women with longer cycles have later ovulation. The follicular phase is the most variable part of the cycle.
What actually helps with timing
Having sperm already there when the egg arrives beats trying to catch the day itself. The two days before ovulation carry the highest chance.
Across the fertile window both work. There is no benefit in saving up, and no need to schedule it to the hour.
Fertile-type mucus says the window is opening. A temperature rise says it has closed. Together they beat the calendar.
Myths worth putting down
Evidence-based fertility tracking methods
Combining multiple tracking methods provides the most accurate prediction of your fertile window. Here are the evidence-based approaches you can use.
Basal body temperature is your lowest resting temperature, which rises approximately 0.3-0.5°C (0.5-1°F) after ovulation due to progesterone.
35.5°C - 36.6°C (96°F - 98°F)
36.1°C - 37.2°C (97°F - 99°F)
One cycle, drawn the way the tracker draws yours. The rise of about 0.4°C appears on day 15, the day after ovulation, which is why temperature confirms ovulation rather than predicting it. The high reading on day 9 is a broken night’s sleep and day 18 was never taken. Real charts look like this, and the pattern still reads clearly across the month.
Key points for accurate BBT tracking
- Take temperature immediately upon waking, before any activity
- Use a basal thermometer showing two decimal places
- Measure at the same time each day
- Ensure at least 3 consecutive hours of sleep beforehand
- Note that illness, alcohol, disrupted sleep, and some medications can affect readings
Lifestyle factors affecting fertility
Lifestyle factors can influence fertility outcomes for both women and their partners. Here are some key areas supported by current evidence.
Both overweight and underweight status can affect fertility. The NHMRC recommends a BMI between 18.5 and 25 kg/m² for general health. Excess body weight can affect ovulation and increase the risk of conditions like PCOS, while being underweight can disrupt hormonal balance and menstrual regularity.
A 2023 Australian-led systematic review found that overall eating patterns, rather than single foods, are what is associated with fertility: a Mediterranean-style pattern showed the strongest and most consistent link with better outcomes, while limiting trans fats and discretionary foods like fast food and sugary drinks was associated with a shorter time to pregnancy. This evidence is observational, so these are associations rather than guarantees. Minerals including zinc, magnesium, and selenium support reproductive health throughout the menstrual cycle.
Moderate regular exercise supports fertility, but extremes in either direction can be counterproductive. Some studies suggest vigorous exercise totalling more than 5 hours weekly may affect ovulation in some women (Wise et al. 2012, Fertility and Sterility). Regular moderate activity is generally beneficial.
Alcohol consumption can negatively influence fertility in both partners. Higher alcohol intake has been associated with reduced conception rates in some studies (Mikkelsen et al. 2016, BMJ Open). For caffeine, preconception research is reassuring: a 2022 study measuring serum caffeine metabolites (Wesselink et al., AJCN) found no association with time to pregnancy, and a systematic review (Bu et al. 2020, BMC Women's Health) found no link between caffeine and infertility at any dose level. Australian guidelines suggest under 200mg/day as a precaution, primarily because some observational data links higher caffeine intake during pregnancy to miscarriage risk (Chen et al. 2015 meta-analysis). However, the most recent large cohort study (Ruderman et al. 2026, BJOG, n=7,345) and Mendelian randomisation analysis (Nunes et al. 2022, IJE) found no causal association with adverse pregnancy outcomes, suggesting the observational signal may reflect confounding.
Smoking has clear negative effects on fertility, reducing ovarian reserve (as measured by AMH levels) and affecting egg quality. Toxins in tobacco smoke, including cadmium and cotinine, can reduce both sperm quality and egg production. Cessation is strongly recommended for anyone planning pregnancy. For free support, call Quitline on 13 78 48.
Chronic stress can affect the hypothalamic-pituitary-gonadal axis, potentially disrupting hormone regulation and menstrual cycles. While establishing a direct cause-effect relationship is challenging, stress management techniques may support fertility. Stress can also lead to other behaviours (poor diet, increased alcohol consumption) that compound fertility effects.
Australian clinical guidelines
These guidelines from Australian medical bodies provide evidence-based recommendations for preconception care and fertility support.
Pre-pregnancy counselling guidelines
Australian pre-pregnancy counselling guidelines recommend:
0.4-0.8 mg daily for women with no risk factors. 5 mg daily for those at increased risk of neural tube defects.
Begin at least 4 weeks before trying to conceive and continue for the first 12 weeks of pregnancy.
150 µg daily prior to planned pregnancy or as soon as pregnancy is discovered.
Women under 35 who haven't conceived after 12 months of trying should be offered referral to a fertility specialist. Women 35 and over should be referred after 6 months.
Review immunisation status before conception, particularly for rubella, varicella, and pertussis.
2024 Australian Guideline for Unexplained Infertility
The 2024 Australian Evidence-based Guideline for Unexplained Infertility defines unexplained infertility as:
The guideline emphasises evidence-based recommendations to help couples make informed decisions and avoid unnecessary treatments.
Official resources
Practical application for cycle tracking
Ready to start understanding your cycle? Here’s a practical guide to getting started with fertility tracking.
Getting started
Record the first day of your period for several months to understand your cycle pattern.
Familiarise yourself with cervical mucus changes and consider BBT tracking.
Use OPKs alongside body-based observations for the most accurate prediction.
It typically takes 2-3 cycles to identify your personal patterns.
Optimising conception timing
Based on the research, intercourse should be timed for the days leading up to ovulation rather than waiting for ovulation day.
When to seek help
Consult a healthcare provider if:
- You’re under 35 and haven’t conceived after 12 months of trying
- You’re 35 or over and haven’t conceived after 6 months
- You have irregular cycles or are not detecting ovulation signs
- You have known medical conditions affecting fertility (PCOS, endometriosis, thyroid disorders)
- You have concerns about your partner’s fertility
Research references
All information on this page is based on peer-reviewed research and clinical guidelines. Below you will find links to the original sources so you can read the research for yourself.
Australian clinical guidelines
Menstrual cycle physiology
Fertile window and ovulation
Fertility tracking methods
Ovulation predictor kits
Lifestyle and fertility
Hormones and reproductive biology
Additional resources
For further reading and support, these Australian resources provide reliable, evidence-based information:
herjourney.com.au · Health education, not medical advice
Evidence: Cochrane, PubMed, RANZCOG, ESHRE · 2013-2026 · © Her Journey 2026