Dr. Aruna Ashok MBBS, MS OG, DNB OG
- Clinical Director
Aruna Ashok | 24 June 2025
If you're trying to conceive, you've probably come across terms like "follicles," "ovulation," or "egg size." But what do these words mean? And why does egg follicle size for conceiving matter so much?
In this article, we'll walk through everything you need to know about egg follicles, how they grow, the ideal size for conception, and how doctors monitor them during fertility treatments. We'll break it down in a way that's easy to understand—no complicated medical jargon here!
Let's start with the basics.
Your ovaries are home to thousands of tiny fluid-filled sacs called follicles. Inside each follicle is an immature egg. During each menstrual cycle, your body chooses one of these follicles to grow and mature. When the time is right, the follicle releases the egg—a process we know as ovulation.
Think of a follicle like a little balloon with an egg inside. As the follicle grows, it gets bigger and fills with fluid. This helps the egg mature properly. If the egg is healthy and meets a healthy sperm, pregnancy becomes possible.
Great question!
Follicle size is closely linked to the maturity of the egg inside. If the follicle is too small, the egg might not be mature enough to be fertilized. If it's too large, the egg may be overripe and less likely to result in pregnancy.
That's why tracking follicle size is an integral part of fertility checkups and treatments. Doctors use ultrasound scans to measure follicles and time ovulation perfectly—especially in couples trying to conceive naturally or through assisted methods like IUI or IVF.
Let's get into the numbers.
In a healthy cycle, the ideal follicle size for ovulation and conception is between 18mm and 24mm in diameter. This size usually indicates that the egg inside is mature and ready to be released.
| Follicle Size | What It Means |
|---|---|
| 10mm – 14mm | Early growth phase, not ready yet |
| 15mm – 17mm | Almost mature, getting close |
| 18mm – 24mm | Ideal for ovulation and conception |
| 25mm or more | Possibly overripe or a cyst |
Doctors usually monitor follicle growth using transvaginal ultrasound starting around day 9 or 10 of the menstrual cycle, depending on your body and treatment plan.
On average, a healthy follicle grows about 1 to 2 millimetres per day once it reaches around 12mm in size. If your follicle is 14mm today, it might be ready for ovulation (18mm or more) in just a couple of days.
This growth rate is essential, especially in treatments like IUI or IVF, where timing is everything.
In natural cycles, your brain releases hormones (FSH and LH) that encourage one follicle to grow. Around the middle of your cycle, the LH surge causes the mature follicle to release its egg. Most women ovulate when their follicle is around 18mm to 22mm.
You can track this with:
In cases where couples need help getting pregnant, doctors may use medications to help the follicles grow or to trigger ovulation. Some standard methods include:
Doctors track follicle size during these treatments to decide the best time for IUI (Intrauterine Insemination) or egg retrieval in IVF (In Vitro Fertilization).
Anjali, a 30-year-old woman from Chennai, had been trying to conceive for over a year. Her doctor suggested a monitored cycle with Clomid. On day 10 of her cycle, an ultrasound showed a 14mm follicle. By day 13, it had grown to 19mm, and her doctor gave her a trigger shot.
Two weeks later, Anjali got the news she had been waiting for—she was pregnant!
This real-life story shows how monitoring follicle size can make a huge difference in planning for pregnancy.
Not every cycle results in the perfect-sized follicle. Here's what can happen:
Sometimes, the follicle doesn't grow large enough for ovulation. This could be due to:
Follicles that grow beyond 24–26mm might not release a healthy egg. This can sometimes happen in women with PCOS or those on fertility medications.
If your follicle size isn't ideal, don't worry—your doctor may adjust your treatment or try a different approach next cycle.
If your doctor is tracking your follicles, you'll likely go through these steps:
Yes! Many women ovulate just one egg per cycle, and that's often all it takes to get pregnant. Even in IVF, a single healthy egg can lead to a successful pregnancy.
The goal isn't always quantity—it's quality. A good-sized, mature follicle with a healthy egg inside can lead to fertilization, implantation, and, hopefully, a baby.
As women age, both the number and quality of follicles decline. That's why follicle tracking becomes more important in women over 35 who are trying to conceive.
Here's a general idea:
That said, many women in their late 30s and even early 40s do get pregnant—especially with monitoring and guidance.
You can't control everything, but small changes can support healthy follicle growth and ovulation:
Supplements like CoQ10, vitamin D, and myo-inositol may also help follicle development—ask your doctor before starting anything new.
Q1: Can I get pregnant with a 16mm follicle?
A 16mm follicle is close to maturity but may still need a few days to reach the ideal 18–24mm range. Ovulation might happen soon after.
Q2: How many follicles do I need to conceive?
One healthy follicle is often enough for natural conception or IUI. In IVF, doctors may aim for multiple follicles to retrieve more eggs.
Q3: What if my follicle doesn't grow?
If follicles aren't growing, your doctor may suggest hormonal tests, lifestyle changes, or medications to stimulate growth.
