Is 15 the Best Number for Egg Retrieval?
Reproductive medicine is still in its infancy, but it’s growing up fast with each new study that’s published. Fascinating research examining the link between live birth rates and the number of eggs retrieved in one in vitro fertilization (IVF) cycle indicate that 15 may be the “magic number” to collect for the most successful outcomes. So, should you and your doctor lock in on this number, or are there other contributing factors you should be aware of? We break down the research, and provide some conclusions and guidelines for you to keep in mind.
A 2011 study published online in the journal Human Reproduction found that there was a strong relationship between live birth rates and the number of eggs retrieved in one IVF cycle. The likelihood of success rose with each additional egg retrieved, up to about 15 eggs. Outcomes leveled off when 15-20 eggs were retrieved, and then steadily declined beyond 20 eggs. The researchers analyzed more than 400,000 IVF cycles that occurred between 1991 and 2008 in the United Kingdom.
Dr. Arri Coomarasamy, an author of the study, and a clinical reader and consultant at the University of Birmingham (UK), pointed out that the study was the first to look at the association between the number of eggs and live birth. He added, “This is also the first study to devise a graph that can be used by patients and clinicians to estimate the chances of a live birth for a given number of eggs.”
Developing Correlations on Egg Retrieval
The UK researchers created a mathematical graph — called a nomogram – that doctors can use to better counsel patients on their probability of a successful outcome from a given IVF cycle. This graph shows the relationship between:
- A woman’s age
- The number of eggs retrieved
- The predicted live birth rate.
The data may be useful, but please be advised that you and your doctor shouldn’t make simplistic interpretations. Not every patient undergoing IVF can — or should — be stimulated toward the production of 15 to 20 eggs.
For example, women over 40 with maximal ovarian stimulation would have trouble reaching this range, whereas young women with polycystic ovarian syndrome (PCOS) will often exceed this range, even with the mildest stimulation. The number of eggs retrieved is ultimately determined by your own ovarian reserve, a medical term that describes your current level of ovarian function.
“There are tests of ovarian reserve, such as anti-mullerian hormone (AMH) and antral follicle count (AFC), which are good at predicting ovarian response and the egg yield following ovarian stimulation during IVF treatment,” according to Dr. Coomarasamy. “However, AMH and AFC are not good predictors of live birth rates. If clinicians use AMH or AFC to estimate the egg yield, they can then use our nomogram to convert this estimated number of eggs into a predicted live birth rate, thus completing the prognostic chain to estimate the chances of what both they and the women want: a live born baby.”
More Eggs Isn’t Always Better
A second study , published in January 2018 in the same journal, further supported the increase in live birth rates based on how many eggs were retrieved. After reviewing the results of 77,956 fresh transfers between 2007-2013 and 36,270 consecutive frozen embryo transfers from 2007-2014, the researchers found that the live birth rate from fresh transfers increased with retrievals of up to 11 eggs.The cumulative live birth rates, which included fresh transfers and all subsequent frozen transfers, increased with each egg retrieved up to 18-20 eggs before leveling off. Keep in mind that these results may be limited, as it’s possible that not every embryo frozen within the study’s timeframe has been transferred yet, and may still result in a live birth.
What’s important to further point out here is the finding that there was a decreased live birth rate when greater numbers of eggs are retrieved — between 15-20. But this assumption may not apply to all types of IVF cycles.
In cases of fresh embryo transfer, the elevated progesterone levels from recent ovarian stimulation may change the environment of the uterine lining, making it less receptive to an implanting embryo. In other words, the stronger the ovarian response to stimulation and the higher the number of eggs retrieved, the more likely it is that the hormonal environment will negatively impact the chance of pregnancy after a fresh transfer. However, in frozen embryo transfers, the embryo transfer occurs in a subsequent cycle, remote from the process of ovarian stimulation. As a result, the hormonal environment more closely resembles a natural cycle. Therefore, the outcome of the frozen embryo transfer is not hindered in patients who had a high number of eggs retrieved in a prior cycle. Of note, this study also looked at the risk of Ovarian Hyperstimulation Syndrome (OHSS). They found that the risk of OHSS increased when more than 18 eggs were retrieved.
So now, in addition to counseling you about your fertility prognosis based on your age and ovarian reserve, your doctor can also weigh in on how the number of eggs retrieved may modify your chances of getting pregnant. The decision of whether to perform a fresh or frozen embryo transfer should be made with your doctor based on your individual health circumstances, and may be influenced by your response to ovarian stimulation and the number of eggs retrieved.
- Sunkara SK, Rittenberg V, Raine-Fenning N, Bhattacharya S, Zamora J, Coomarasamy A. Association between the number of eggs and live birth in IVF treatment: an analysis of 400 135 treatment cycles. Hum Reprod. 2011;26(7):1768-1774. https://doi.org/10.1093/humrep/der106. Accessed July 9, 2018.
- Magnusson Å, Källen K, Thurin-Kjellberg A, Bergh C. The number of oocytes retrieved during IVF: a balance between efficacy and safety. Hum Reprod. 2018;33(1):58–64. https://doi.org/10.1093/humrep/dex334. Accessed July 9, 2018.
Dr. Lucky Sekhon is a reproductive endocrinologist and infertility specialist and board-certified obstetrician and gynecologist. She specializes in diagnosing and treating reproductive issues and has particular expertise in fertility preservation (egg freezing), LGBTQ family building, and in vitro fertilization with preimplantation genetic testing of embryos. She also uses minimally invasive techniques such as laparoscopy and hysteroscopy to treat a variety of surgical conditions including endometriosis and uterine factor infertility.