When and How Fertility Declines?

Most of us grow up hearing about “the biological clock” in vague terms - usually without any clear explanation of what it actually means. Is it a sudden cliff at 35? Is it the same for everyone? And how do you even know where you stand?

Let’s break it down with facts, not fear.

Fertility changes over time - but it’s not a light switch

Women are born with all the eggs they’ll ever have - around 1 to 2 million at birth. That number declines naturally over time. By puberty, you have about 300,000 to 500,000 eggs left. Most won’t ever be ovulated, and the ones that remain gradually decrease in both quantity and quality as you age.

For many women, fertility starts to decline in the early 30s, with a steeper drop after 35. But this isn’t an overnight change - it’s a gradual process influenced by your genetics, health, lifestyle, and sometimes underlying conditions like PCOS or endometriosis.

Quantity and quality matter

Egg quantity (ovarian reserve) is important, but so is egg quality - the likelihood that an egg can develop into a healthy embryo. As you get older, the proportion of eggs with chromosomal abnormalities increases. This is one reason miscarriage risk rises and it may take longer to conceive.

The “average” timeline - and why it’s only a guide

• 20s: Peak fertility for most women. Monthly chance of pregnancy is highest, around 25-30% with regular unprotected sex.
• Early 30s: Small but measurable decline in fertility.
• Mid-to-late 30s: Decline becomes steeper.
• 40s: Conception becomes more difficult for most, and miscarriage risk increases.

But here’s the important part: these are averages. Some women’s fertility declines sooner, others later - and you can’t know exactly where you are on the curve without more information.

How to get a clearer picture of your fertility

Fertility isn’t something you have to guess about. Hormone testing can give you insights into your ovarian reserve and overall reproductive health:

• AMH (Anti-Müllerian Hormone): A key indicator of ovarian reserve.
• FSH and LH: Involved in egg development and ovulation.
• Estradiol: Can provide context to FSH results.

These aren’t predictions of whether you can or can’t get pregnant, but they can help you plan ahead, make informed decisions, and have better conversations with your doctor.

With Strawberry Health, every member who completes our at-home fertility test receives a Personalized Fertility Timeline - a clear, science-based view of how your fertility may change over time, based on your hormone levels and age. It’s designed to help you understand your reproductive health today and make informed choices for your future, whether that’s trying soon, freezing eggs, or simply tracking changes over time.

The takeaway

Fertility decline is real, but it’s not a one-size-fits-all story - and it’s not something to fear. The more you understand your own reproductive health, the more options you have. Whether you’re thinking about starting a family soon, exploring egg freezing, or just want to be proactive, it starts with knowing your numbers.

An at-home test is an easy first step. With Strawberry Health, you can skip the waitlists and awkward clinic visits, get accurate results from the comfort of your home, and walk away with your own Personalized Fertility Timeline - a tool designed to give you clarity, confidence, and options for your next chapter.