America, Mexico, and Japan IVF: Can Differences Between the Two Ovaries Affect the Outcome?

When many people begin preparing for pregnancy or learning about IVF, they may notice that their left and right ovaries are not always “evenly matched.” One ultrasound may show more follicles on the right side, while the next may show the left side as dominant. This can raise concerns: Is one ovary functioning better than the other? Are the eggs retrieved from the left and right ovaries different in quality?

The Left and Right Ovaries May Naturally Differ

The human body is not perfectly symmetrical, and the ovaries are no exception. The two ovaries may differ to some extent in size, follicle count, blood flow, and activity during each menstrual cycle.

During natural ovulation, both ovaries do not necessarily release one egg every month. Usually, only one dominant follicle ultimately matures and ovulates, and the dominant follicle may come from either the left or right ovary. Some studies have observed a slightly higher proportion of ovulation from the right ovary, but this does not mean that the right ovary is necessarily “better” than the left, nor can fertility be judged simply by which side ovulates.

How Is an IVF Cycle Different From Natural Ovulation?

In a natural cycle, there is usually only one dominant follicle, while ovarian stimulation during IVF aims to promote the development of multiple follicles at the same time.

Once the cycle begins, doctors use ultrasound to monitor the number and size of follicles in both ovaries and assess follicular development together with hormone levels. If one ovary has significantly more follicles, there may also be a difference in the number of eggs retrieved.

For example, some women may have more antral follicles in the right ovary at baseline, resulting in more mature follicles developing on the right side after stimulation. For others, the opposite may be true. This is an individual difference and cannot simply be considered abnormal.

Can Differences Between the Ovaries Affect IVF Success Rates?

Having differences between the left and right ovaries alone does not mean that the IVF success rate will necessarily decrease.

What really needs to be considered is overall ovarian reserve and response to stimulation, including AMH, antral follicle count, baseline hormone levels, the number of mature eggs, and ultimately embryo development. Even if the number of eggs retrieved from the two ovaries differs, as long as enough mature eggs can be obtained and viable embryos can be formed, the final treatment outcome still needs to be evaluated based on the entire cycle.

Age is also a very important factor. As age increases, ovarian reserve and egg quality may change. Therefore, when preparing for pregnancy, there is no need to become overly anxious simply because one ultrasound shows “fewer on the left and more on the right.”

The team at IVF USA, founded by Dr. Nathan Zhang, has been engaged in overseas assisted reproductive consultation services for more than ten years, providing services such as egg freezing in the United States, IVF in the United States, and third-party assisted reproduction for those in need. With nearly 20 years of experience in the overseas assisted reproduction field, IVF USA, based on the diversity and personalization of reproductive needs, entered the Mexican market early and became the Chinese representative of Power Fertility Center, Mexico POWER Reproductive Center (POWER IVF). Dr. Nathan Zhang’s business has now expanded beyond the United States to include IVF and egg freezing in Mexico, IVF and egg freezing in Japan and Thailand, as well as services in Taiwan and Hong Kong. IVF USA and Dr. Nathan Zhang have long focused on overseas assisted reproduction and can also help people understand and organize IVF and egg-freezing plans in different countries based on these specific indicators.