Ovarian Follicle Ultrasound: Here’s What You Need to Know

What is an ovarian follicle ultrasound?

An ovarian follicle ultrasound, also known as follicular tracking or monitoring, is a non-invasive imaging procedure used to assess the development and growth of ovarian follicles during a woman's menstrual cycle. This type of transvaginal ultrasound scan provides detailed images of the ovaries and uterus to treat fertility issues.

What does an ovarian follicle ultrasound detect?

Ovarian follicle ultrasound is used by your healthcare provider to detect and monitor several key aspects of your reproductive organ health, such as:

1. Number of follicles in each ovary

2. Size and growth rate of individual follicles

3. Identification of the dominant follicle

4. Thickness of the endometrial lining

5. Timing of ovulation

6. Presence of any abnormalities in the ovaries or uterus

What are ovarian follicles?

Many people mistakenly think that ovarian follicles and eggs (oocytes) are the same, but they are not. A follicle is a functional anatomical structure which forms part of the ovary, while the egg is the cell that will grow and mature in the inner wall of a follicle.

In addition, the ovarian follicles contain other cell types which produce oestrogen, which is necessary for the normal development and maturation of the egg. The number of eggs is determined at birth,  which means women have afinite number of follicles, typically a few hundred thousand, which gradually decline with age. 

During each menstrual cycle, a group of follicles begins to develop, with usually only one reaching full maturity and releasing an egg during ovulation. Each subsequent menstrual cycle will usually result in a relatively inferior egg quality, which explains why older women have more difficulty getting pregnant and have higher miscarriage rates.

Why is it important to monitor ovarian follicles?

Monitoring ovarian follicles is crucial for several reasons:

1. Pinpointing time of ovulation more accurately

2. Guiding fertility medication dosage and timing

3. Reducing the risk of multiple pregnancies during fertility treatments

4. Detecting issues such as low ovarian reserve or ovulation disorders

5. Optimally timing fertility procedures like intrauterine insemination (IUI) or egg retrieval for in vitro fertilisation (IVF)

By closely monitoring follicular development each cycle, the most fertile days can be identified more accurately. Thus, maximising the chances of successful conception through timed intercourse or infertility treatments.

Why is follicular ultrasound important in IVF?

Follicular tracking is crucial in IVF for several important reasons outside of providing the optimal time for egg retrievals. It also helps with:

• Medication management

  • Tracking allows doctors to monitor the effects of fertility medications on follicle growth and oestrogen levels, enabling them to adjust doses as needed to optimise responses and reduce the risk of ovarian hyperstimulation syndrome (OHSS).

• Customisation of treatment

  • By closely monitoring each patient's unique response to stimulation, doctors can personalise the IVF protocol and make adjustments to improve outcomes over multiple cycles if necessary.

• Maximising egg yield

  • Meticulous tracking helps produce the maximum number of quality mature eggs for retrieval, increasing the yield of viable embryos.

• Reducing cycle cancellation

  • Thorough monitoring ensures adequate follicular development, reducing the likelihood of cycle cancellation and the associated emotional and financial costs.

• Improving success rates

  • Intensive monitoring may help lower miscarriage rates and improve live birth outcomes by optimising egg maturation and growth patterns.

• Guiding critical decisions

  • Follicular tracking provides essential information for timing the administration of ovulation-triggering hormones and determining the ideal day for egg retrieval.

• Early detection of issues

  • Regular monitoring can identify potential problems early, such as poor ovarian response or overresponse, allowing for timely interventions.

By providing crucial information about follicle growth, egg maturity, and the overall ovarian response, follicular tracking plays a vital role in optimising IVF outcomes and increasing the chances of successful pregnancy.

If you’re undergoing IVF or planning to do so, don’t hesitate to request an appointment with Thomson Medical. Our specialist will help guide you through this fertility treatment and provide tailored fertility recommendations.

How do I prepare for the ultrasound?

The preparation for a follicular tracking ultrasound is often minimal:

1. For a transvaginal ultrasound, you may be asked to empty your bladder before the procedure.

2. Wear comfortable, loose-fitting clothing.

3. No fasting or special dietary restrictions are required.

What happens during the ultrasound?

During the ultrasound:

1. You'll lie on an examination table.

2. A small, lubricated transvaginal probe will be gently inserted into the vagina.

3. During the ultrasound, your doctor will measure the size and count the number of follicles developing in your ovaries. They will also measure the thickness of your endometrial lining.

4. The procedure usually takes about 10-15 minutes.

Tracking scans are typically performed every 1-3 days at the start of your fertility treatment cycle. Your doctor will monitor how your follicles are responding to the fertility medication you are taking. Once the follicles have reached a mature size, your final scan will indicate the ideal timing for your egg retrieval or ovulation trigger shot. This is known as your “trigger scan”.

Some clinics will also perform blood tests on the day of your scan to measure oestrogen levels. Oestrogen rises as the follicles grow, so blood levels provide additional information.

How do I interpret the results of my follicular tracking scan?

Your fertility specialist will interpret the results for you, considering:

Follicle size

• Follicle size indicates the stage of egg maturation. Bigger follicles contain more mature eggs. Ovarian follicles are often measured across their widest diameter. The ideal follicle size is between 16 and 22 mm before egg retrieval.

• If the follicles are too small, it could indicate immature eggs, meaning they need longer stimulation. While follicles that are too large may indicate overly mature eggs, which could pose a risk of spontaneous ovulation.

Follicle number

• The number of follicles reflects your ovarian reserve and response to medications. A higher number of mature-sized follicles means there are more eggs that can be retrieved. A number of 10 or more mature follicles is considered a good response, while less than 3 mature follicles is considered a low response.

• If there is a low response, it may indicate low ovarian reserve or poor stimulation. If there is a too high of a response, it may indicate a risk of ovarian hyperstimulation syndrome (OHSS)

Lining thickness

• The endometrial lining must thicken to support embryo implantation. The lining is measured from the outer edge across the full width, and the ideal thickness is usually around 8mm or greater by trigger day.

• If the lining thickness is too thin, it may prevent embryos from implanting. While an excessively thick lining may indicate the presence of polycystic ovary syndrome (PCOS) and hinder implantation.

Oestrogen levels

• Oestrogen levels rise as follicles develop and increase in size. Oestrogen levels are often measured in pg/mL or pmol/L. Your clinic will be looking for levels to rise steadily over your monitoring period.

• High levels of oestrogen may indicate OHSS risk, while low levels may reflect poor response to treatment.

These factors will guide decisions about fertility treatments, medication adjustments, and timing of procedures.

It's important to consult with your fertility specialist to determine if an ovarian follicle ultrasound is suitable for your fertility condition. Request an appointment with our fertility specialist at the Thomson Fertility Centre for personalised fertility recommendations.

What do the ideal scan results look like?

Follicle and lining measurements will vary throughout your treatment cycle as you progress from medications to ovulation or retrieval. Here's what to expect:

• Baseline scan

  • A baseline scan is usually performed at the start of your fertility treatment cycle before medications begin. It determines the antral follicle count (AFC), which is the number of resting follicles in your ovaries.

  • It will confirm that the ovaries are inactive, without any large egg sacs ready for release, and the uterus has a thin lining. Additionally, oestrogen hormone levels will be low.

• After 5 to 7 days of stimulation

  • After 5 to 7 days of treatment, small fluid-filled sacs in the ovaries, called follicles, will start to grow and reach about 10mm in size. Ideally, one follicle may become larger, measuring at least 12mm, while the lining of the uterus thickens to around 5mm. Hormone levels, especially oestrogen, will also begin to increase.

• Final scan before trigger

  • At the last ultrasound before the fertility medication trigger shot, doctors want to see several developed egg sacs (follicles) measuring between 16 and 22 mm. Ideally, one or more leading follicles should reach at least 18mm. The uterus lining should be at least 8mm thick with a clear three-layer appearance (like a sandwich with distinct lines). Hormone levels (oestrogen) should match the number and size of growing follicles.

  • These results indicate you are ready to proceed with egg retrieval or your ovulation trigger shot. However, it is important to note that your ideal results will depend on your age and diagnosis.

What are potential issues that the scan can identify?

Follicular tracking scans can identify several potential issues:

• Poor response: Few or no follicles growing with low oestrogen, indicating low ovarian reserve

• Over-response: Too many follicles developing rapidly, risking OHSS

• Premature luteinisation: LH surge before trigger, leading follicles to luteinise earlier, risking early oocyte maturation

• Thin endometrial lining: Inadequate thickening, potentially preventing embryo implantation

• Ovarian cysts: May require cycle cancellation or conversion to IUI

Your doctor will discuss any issues seen on your scan and recommend protocol adjustments as needed.

What are some of the next steps I can take after my scan if I have abnormal results?

Your doctor will review your follicular development, lining thickness, oestrogen levels, and any issues identified on your scan. They will then advise you on the necessary next steps:

• Continue monitoring

  • If follicles are still growing, you will return in 1-3 days for your next scan to track continued progress.

• Adjust medications

  • Changes in medication dosing may be made to improve follicle growth and development or prevent over-response.

• Schedule retrieval or trigger

  • When follicles have reached maturity, retrieval or trigger will be scheduled within the next 36 hours.

• Cycle cancellation

  • Your doctor may stop the cycle if there are too few follicles, poor lining, or excess risk of complications like OHSS.

• Egg freezing

  • If the follicular response is excessive or other issues arise, like premature luteinisation, egg freezing  may be recommended. A frozen embryo transfer can be performed later with proper hormonal priming.

Understanding what to look for in your follicular tracking scan results will help you know what to expect throughout your IVF or IUI cycle. Discuss your results thoroughly with your doctor and don't hesitate to ask questions. Tracking your follicle growth and cycle response empowers you to be an informed and engaged patient.

FAQ

Do follicular tracking scans hurt?

Follicular tracking scans are generally not painful, though you may experience mild discomfort during the insertion of the transvaginal probe.

What does it mean when you see follicles on your ovaries?

Seeing follicles on your ovaries is normal and indicates that your ovaries are functioning. The number and size of follicles provide information about your ovarian reserve and cycle progression.

How many follicles in each ovary is normal?

The number of follicles considered normal varies depending on age and individual factors. Generally, having 5 to 10 small egg sacs, or antral follicles, per ovary is considered within the normal range.

How many follicles are normal on ultrasound?

During a natural cycle, it's normal to see one dominant follicle and several smaller follicles. The number can change depending on the stimulation protocol used in fertility treatments.

How many follicles indicate PCOS?

PCOS is often characterised by the presence of 12 or more follicles measuring 2–9 mm in diameter per ovary or by an increased ovarian volume of >10 mL.

How will my doctor adjust my medications for a thin lining?

If your endometrial lining is thin, your doctor may adjust your medications to include oestrogen supplements or increase the dosage of fertility drugs to promote lining growth.

What happens if my follicles are too small on the final scan?

If follicles are too small on the final scan, your doctor may extend your stimulation period or adjust medication dosages to promote further growth.

When should I trigger if my follicle size is borderline?

The decision to trigger ovulation is based on multiple factors, including follicle size, endometrial thickness, and hormone levels. Your doctor will determine the optimal timing based on your individual circumstances.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical today.