What Nobody Tells You About Fertility After 35 (Part 2): 5 More Things We Learned the Hard Way

Part 1 of this article covered five things we wish we had known earlier: the 90-day egg maturation window, cycle-phase nutrition, the role of stress and cortisol, the difference between folate and folic acid, and the gap between fertility research and what doctors actually tell you.

We received so many responses from women who said "nobody told me this either" that we decided to write part 2.

Dorothy is 40 and we are still on this journey. These are five more things we have learned - all backed by research, none of them told to us upfront.

1. Ovulation probably does not happen on day 14 - and assuming it does can make you miss your window entirely

The "day 14" rule is one of the most persistent myths in fertility.

It comes from averaging a 28-day cycle and dividing it in half. But research consistently shows that most women do not have 28-day cycles - and even those who do do not necessarily ovulate on day 14.

A study analysing over 600,000 cycles from Natural Cycles found that only 13% of women had a 28-day cycle. The average ovulation day across all cycle lengths was day 16.9 - not day 14. For women with cycles of 31 to 35 days, the average ovulation day was day 19.5.

The American Pregnancy Association is direct on this point: day 14 thinking comes from averaging data across all women, and it is not an accurate way to calculate ovulation for any individual woman. For a woman with a 28-day cycle, the window of ovulation spans day 11 through day 21.

A separate analysis of 2.7 million cycles found that only 24% of ovulations occurred on day 14 or 15.

What this means practically:

If you are timing intercourse around day 14 based on a calendar and you actually ovulate on day 18 or 19, you are consistently missing your fertile window. This is one of the most common and easily fixable mistakes women make when trying to conceive.

LH testing, BBT tracking, and cervical mucus observation are the only reliable ways to identify your actual ovulation day. This is exactly why FertiNutrition's cycle tracking includes all three - because calendar-based predictions simply are not accurate enough for most women.

2. Alcohol has more impact on egg quality than most doctors mention

This is not about judgement. It is about information that does not always make it into a standard fertility consultation.

Research published in Reproductive Science in 2024, reviewing molecular mechanisms of alcohol-induced female infertility, found that chronic alcohol consumption disrupts hormonal balance, impairs egg maturation, and increases oxidative stress in ovarian follicles - all of which directly affect egg quality.

A separate review of six epidemiological studies on alcohol and assisted reproduction, published in Fertility and Sterility, found that three of those studies observed a negative effect of current alcohol consumption on fertilisation rates, embryo quality, and implantation.

For women undergoing IVF specifically, alcohol intake has been associated with up to 13% fewer eggs retrieved per cycle.

The UK's National Institute for Health and Care Excellence (NICE) recommends that women trying to conceive limit alcohol to no more than one to two units once or twice per week. But the honest summary of the research is that no safe lower limit has been established for women who are actively trying to conceive.

What we did:

Dorothy stopped drinking entirely during the 90 days we treated as our most focused nutritional window. This was a personal choice, not a medical prescription. What we found was that it removed a variable we could not otherwise control.

3. Your thyroid has a direct effect on your cycle - and many women are never tested

The thyroid is a small gland in the neck that regulates metabolism, energy, and hormonal balance. What is less commonly known is how directly it affects reproductive function.

A 2024 Mendelian randomisation study published in Frontiers in Endocrinology confirmed a causal association between thyroid dysfunction and infertility risk in women. Thyroid hormones interact with nuclear receptors in reproductive organs, directly modulating their development and function.

A 2025 narrative review in PMC, covering 67 studies published between 2020 and 2025, found that both hypothyroidism and thyroid autoimmunity are prevalent in women of reproductive age and are independently associated with adverse fertility outcomes, including irregular cycles, anovulation, and higher miscarriage rates.

The challenge is that subclinical hypothyroidism - where thyroid function is impaired but not severely enough to cause obvious symptoms - is common and frequently undetected in standard fertility workups.

What we recommend discussing with your doctor:

Ask specifically for a full thyroid panel including TSH, T3, T4, and anti-TPO antibodies. A standard TSH test alone may not capture subclinical dysfunction. This is a conversation worth having, particularly if you have irregular cycles, fatigue, or difficulty maintaining weight.

4. Magnesium deficiency is almost universal in women who are TTC - and it affects more than you think

Magnesium is one of the most important minerals for reproductive health, and one of the most commonly deficient.

Research on micronutrients and female fertility consistently finds that magnesium plays a role in:

• Regulating the stress response and cortisol levels
• Supporting progesterone production in the luteal phase
• Reducing PMS symptoms including cramping and mood changes
• Improving insulin sensitivity, which affects hormonal balance

The 2025 comprehensive review in Nursing Research and Practice on micronutrients and female fertility highlighted magnesium alongside folate and iron as among the most clinically relevant nutrients for reproductive function - and among the most commonly insufficient in women of reproductive age.

A significant reason for widespread deficiency is dietary. Processed foods, refined grains, and depleted soils have reduced the magnesium content of modern diets substantially compared to a century ago.

Foods highest in magnesium:
Dark chocolate, pumpkin seeds, almonds, spinach, black beans, avocado, brown rice.

In FertiNutrition:
Magnesium-rich foods are specifically prioritised in the luteal phase meal plans, when progesterone support and cortisol regulation are most relevant.

5. The luteal phase is the most nutritionally neglected phase - and it may be the most important

Most fertility nutrition advice focuses on the follicular phase and ovulation - the run-up to the egg's release. But what happens after ovulation is equally critical and far less discussed.

The luteal phase is the two weeks between ovulation and the start of your next period. During this time:

• The corpus luteum produces progesterone to prepare the uterine lining for implantation
• If fertilisation has occurred, the embryo needs a supportive hormonal environment to implant
• Blood sugar stability becomes particularly important - fluctuations can affect mood, energy, and hormonal balance

A luteal phase defect - where progesterone production is insufficient - is one of the more common causes of early pregnancy loss and implantation failure. Nutrition does not replace medical treatment for a luteal phase defect, but it can support the hormonal environment that progesterone production depends on.

What supports the luteal phase nutritionally:

• Magnesium - supports progesterone and reduces cortisol
• Vitamin B6 - involved in progesterone synthesis and mood regulation
• Complex carbohydrates - sweet potato, brown rice, oats - stabilise blood sugar and support serotonin
• Zinc - supports corpus luteum function

The 2025 Nursing Research and Practice review confirmed that B vitamins, including B6, play a role in hormonal regulation and are among the nutrients most consistently associated with reproductive outcomes.

What most apps get wrong:

Most cycle tracking apps tell you when your luteal phase starts and ends. Very few tell you what to eat during it - or why it matters as much as the days around ovulation.

That is the gap FertiNutrition is specifically built to address.

What this means for us

Dorothy is 40. We are still on this journey. Part 1 and Part 2 of this article are not a success story - they are a work in progress.

What we know is that we are making informed decisions every day. The app tells Dorothy what phase she is in and what to eat. The meal plans are built around the nutrients that matter for that specific phase. The tracking shows whether she is hitting her targets.

We cannot control everything. But we can control this.

The full journal is at fertinutrition.com/journal. The app is available on the App Store with 7 days free to explore.

References

1. Natural Cycles / Bull et al. Cycle variability and ovulation day analysis across 600,000+ cycles. Referenced in: Period tracker applications: What menstrual cycle information are they giving women? PMC. 2021.
2. American Pregnancy Association. Ovulation FAQs - the day 14 myth. americanpregnancy.org. Updated February 2026.
3. Minguez-Alarcon L, Chavarro JE et al. Caffeine, alcohol, smoking, and reproductive outcomes among couples undergoing ART. Fertility and Sterility. 2018;110(4):587-592. doi:10.1016/j.fertnstert.2018.05.026. PMC updated 2024.
4. Reprod Sci. Investigation of Uncovering Molecular Mechanisms of Alcohol-Induced Female Infertility. 2024;31(12):3660-3672. doi:10.1007/s43032-024-01692-8
5. Liu Q, Qiu Y et al. Causal association between thyroid function and the risk of infertility: a Mendelian randomization study. Frontiers in Endocrinology. 2024;15:1425639. doi:10.3389/fendo.2024.1425639
6. PMC. Research on the Impact of Thyroid Disorders on Reproductive Function: A Narrative Review. 2025. pmc.ncbi.nlm.nih.gov/articles/PMC12434935
7. Mashhadi et al. Nutritional Interventions for Enhancing Female Fertility: A Comprehensive Review of Micronutrients and Their Impact. Nursing Research and Practice. 2025. doi:10.1155/nrp/2137328
8. European Food Safety Authority (EFSA). Dietary Reference Values. efsa.europa.eu

FertiNutrition is a nutrition tool, not a medical product. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider or fertility specialist for personalised guidance.

Download FertiNutrition on the App Store - 7 days free to explore.