I’ll be honest: when I first saw that stat, I was shocked. Maybe because I grew up in the ’80s and ’90s—when teen pregnancy was framed as the crisis, and fertility after 35 was barely mentioned, let alone supported.
Robin’s Short Version
- Blood Sugar First: Even mild insulin resistance—before diabetes—disrupts ovulation, lowers progesterone, and raises miscarriage risk, even in women with normal cycles and a healthy BMI.
- Post-Meal Walks Work: Walking just 10–15 minutes after eating pulls glucose from the blood directly into muscles, making it one of the fastest ways to stabilize blood sugar.
- TSH Isn’t Enough: A “normal” TSH above ~2.0 can still impair fertility—a complete picture requires Free T4, Free T3, Anti-TPO, and Anti-thyroglobulin antibody testing.
When I graduated from med school at Columbia in 2011, IVF was just becoming mainstream and I began to see patients dealing with infertility and impaired fertility. I quickly realized that conventional medicine offered them two choices:
- Wait until you hit the 12-month mark of trying
- Or go straight to IVF
Both options skipped right over why fertility might be impaired in the first place.
Now, after helping thousands of women get pregnant—naturally and via IVF—I can confidently say:
Fertility isn’t a black box. It’s a system. And it’s modifiable.
Age matters. But it’s far from the whole story. I got pregnant for the first time just shy of 35, and went on to have three full-term, healthy pregnancies between 35 and 40—with no interventions. Yes, that’s anecdotal—but it mirrors what I see daily in my clinical practice at Parsley Health.
Yes—there are factors we can’t control. And that reality deserves honesty and compassion. But there is also so much that is in our control—the healthcare system has largely failed to address the root drivers of declining fertility or to help women optimize the terrain before they ever reach a fertility clinic.
So let’s talk about the levers most doctors still aren’t pulling.
⚡️ Forward this protocol
If you only do one thing to optimize fertility over 35, do this:
🩸Test and stabilize your blood sugar.
Even mild insulin resistance—before diabetes—disrupts ovulation, lowers progesterone, impairs egg quality, and increases miscarriage risk.
This is true even in women with “normal” cycles and a healthy BMI.
The 4-week blood sugar reset:
- Eat 30–40g protein at breakfast (skipping this worsens glucose spikes throughout the day)
- Eliminate ultra-processed carbs and added sugar
- Walk for 10–15 minutes after meals (pulls glucose from the blood into muscles)
- Lift weights 2–3x/week to improve insulin sensitivity and “sink” glucose into muscles
- Protect sleep (poor sleep raises insulin resistance within days)
Blood sugar is one of the fastest, most measurable fertility levers we have—and improving it often unlocks everything else.
🤓 What to know: Fertility over 35 is more modifiable than you’ve been taught.
Fertility isn’t just a reproductive issue—it’s a whole-body process. Ovulation, implantation, and early pregnancy depend on finely tuned signals between your brain, ovaries, thyroid, immune system, and metabolism.
In my practice, these are the most overlooked—but modifiable—drivers of impaired fertility:
🧁 Blood sugar & metabolic health
Even in women without diabetes, subclinical insulin resistance is associated with irregular cycles, anovulation, and miscarriage risk (Human Reproduction, 2024).
Insulin resistance affects fertility through several pathways:
- Impaired ovulation and follicle development (Lancet Diabetes Endocrinology, 2020)
- Oxidative damage to egg quality (Human Reproduction, 2012)
- Endometrial disruption that contributes to implantation failure (PLoS One, 2017)
🌀 Thyroid function
Thyroid hormones act as master regulators of reproduction. They influence:
- Ovulation timing
- Luteal phase adequacy
- Implantation
- Placental development
👉 Overt hypothyroidism is associated with menstrual irregularities and infertility (Thyroid, 2017).
👉 Untreated hypothyroidism disrupts ovulation, causes infertility, and increases miscarriage risk (JAMA, 2025).
👉 Thyroid autoantibodies are associated with diminished ovarian reserve and increased miscarriage risk (Seminars in Reproductive Medicine, 2024).
🔥 Chronic inflammation
Chronic, low-grade inflammation interferes with fertility at multiple levels.
Unlike acute inflammation, this type often flies under the radar, creating a systemic inflammatory state that directly compromises reproductive processes:
- Inflammatory cytokines disrupt folliculogenesis, reduce oocyte quality through oxidative stress, and interfere with hormone production (Reproduction, 2025).
- “Leaky gut” may trigger ovarian inflammation and impair luteal phase (Gynecological Endocrinology, 2015)
- Gut dysbiosis contributes to elevated estrogen levels, which can promote conditions like endometriosis (International Journal of Molecular Sciences, 2024)
❌ Autoimmune activity
Autoimmunity can impair fertility even in the absence of symptoms. (Women account for ~80% of autoimmune disease.)
- Promotes a chronic inflammatory environment that impairs implantation (Journal of Clinical Medicine, 2024).
- Antiphospholipid antibodies (aPL) can cause pregnancy loss (Clinical Immunology, 2011).
😧 Chronic stress & nervous system dysregulation
Fertility requires safety, biologically speaking.
Chronic stress activates the hypothalamic-pituitary-adrenal (HPA) axis, which can:
- Suppress ovulation (Psychoneuroendocrinology, 2018)
- Chronic stress reduces progesterone through precursor competition—the so-called “cortisol steal” mechanism (Comprehensive Physiology, 2025).
- Stress-induced progesterone deficiency leads to luteal phase insufficiency (Epidemiology, 2015).
💪 What to do: 8 evidence-backed fertility levers to tackle now.
✅ 1. Optimize blood sugar
- Hemoglobin A1C: < 5.4%
- Fasting insulin: < 5 µIU/mL
- Fasting glucose: ~80 mg/dL
✅ 2. Test and treat thyroid conditions the right way
Test beyond TSH:
- Free T4
- Free T3
- Anti-TPO antibodies
- Anti-thyroglobulin antibodies
A TSH above ~2.0 may be considered “normal” by labs but can still impair fertility. Treatment often requires both medication and targeted nutrient repletion (iron, selenium, iodine, zinc).
✅ 3. Use cyclic progesterone to reset irregular cycles
Women with PCOS, hypothyroidism, metabolic dysfunction, or chronic stress often have low or erratic progesterone.
“Cyclic” progesterone—14 days on, 14 days off—can help:
- Normalize cycle length
- Improve luteal phase support
- Reduce estrogen dominance
⚠️This is very different from continuous progesterone and should be used thoughtfully with a clinician.
✅ 4. Eliminate food-driven inflammation
A significant percentage of people have undiagnosed food sensitivities driving chronic inflammation—often without obvious GI symptoms.
The most common culprits:
- Gluten
- Dairy
- Soy
- Eggs
- Corn
- Nightshades
Tools like KBMO food sensitivity testing (which we use at Parsley) or blood-based allergy testing can help personalize this—rather than guessing forever.
✅ 5. Actively downshift your nervous system (this is not optional)
Chronic stress can lead to “cortisol steal,” where progesterone is diverted to make more cortisol—directly impacting fertility.
Your goal: 60 minutes per day in a parasympathetic-dominant state.
That can look like:
- Walking
- Yoga
- Breathwork
- Cooking
- Meditation
- Gentle strength training
- Any non-screen, non-performance activity
✅ 6. Screen early for autoimmune activity
Key labs to consider:
- ANA
- hs-CRP
- ESR
- Thyroid antibodies
Identifying and calming immune activation early can be fertility-protective.
✅ 7. Reduce toxin exposure that disrupts hormones
Many everyday chemicals are known endocrine disruptors which interfere with estrogen, progesterone, and thyroid signaling:
- Parabens
- Phthalates
- BPA / BPS
- PFAS
- Microplastics
👉️ Use the Environmental Working Group app for pregnancy-safe products
👉️ Filter drinking water (ideally reverse osmosis)
👉️ Prioritize fiber (30-50g) to help clear microplastics
✅ 8. Move your body—strategically
Exercise is one of the most powerful tools we have to:
- Improve insulin sensitivity
- Balance hormones
- Reduce stress
- Normalize cycles
The protocol:
- Strength training (2–3x/week)
- Yoga or mobility work (1-2x/week)
- Zone 2 cardio (brisk walking, cycling)
💛 The Momgevity Files
This morning, my 4-year-old got in bed with me to snuggle. It’s a snow day here in NYC, and all three of my kids are home from school. As I cuddled with him and looked out at the gray sky, I couldn’t help but feel a pang of what I call pre-nostalgia—that sense of missing something from the perspective of the future, even though it’s still here now.
Thinking back to when I had my first child and was starting Parsley Health, I remember fearing that kids would limit me—that they’d keep me from doing the things I wanted to do, or somehow cut off a part of myself I’d lose forever.
What I’ve learned is that kids are part of the expansion: I became a mother and a CEO, a caretaker and a creator—a foundation for someone else’s life that, in its broadness, widened my ability to live a bigger version of my own. I wasn’t less for having kids. I became far more than I ever could have imagined.
As crazy and overwhelming as this time of life feels sometimes—raising young kids, work in full steam, travel, partnership, social life all in motion—I keep coming back to this idea of expanding into more of myself, again and again.
A mom friend recently asked how I find time to commit to a longevity routine, given how full life is. She was like, “I’m calling BS. How on earth do you actually lift weights, do Pilates, take supplements, meditate, work with a spirituality coach, sauna, and do any actual Zone 2?! Come ON.”
She has a point. I don’t get to all of it, all the time, or every week. I went to yoga yesterday for the first time in two weeks, and my body was so grateful. I’d missed my mat terribly (it’s the spot where I really ground and tune in to myself), but my schedule simply hadn’t allowed it. And that’s okay. It all comes in waves.
On the flip side, all of these practices are what allow me to expand. They’re how I sleep well, find energy, gain clarity and calm, and maintain resilience and stamina for a big life. Without them, I start to feel tired, foggy, bloated, anxious, and erratic.
Longevity, for me, is about constantly becoming the best version of myself—challenging my assumptions of who I think I have to be, and listening to what I really want.
The longevity practices I’m leaning into, then, aren’t just about long-term brain health or preserving muscle mass. They’re about fully living the life I have now—especially because these moments of snuggles with my little ones won’t last forever.
Stay strong, stay curious and breathe,
Robin
⚡️ One last thing…
Optimizing your fertility at any age doesn’t have to be a DIY project. This is a core part of what we do at Parsley. We get referrals from IVF clinics all the time to help patients optimize their health and increase their likelihood of treatment. We have helped hundreds of women get pregnant!
Learn more about our reproductive health program here.
👋 I’m Dr. Robin Berzin
I’m a mom, wife, doctor, and CEO in my 40s. My goal is to be healthier than ever – and help you do the same.
I’m also the founder of Parsley Health, the nation’s leading functional medicine clinic designed to help you reverse chronic disease and optimize your health.
Join Parsley using RBMDCREW to save $100 on your membership.
