Low egg maturity ratios linked to reduced live birth rates

Researchers in a 2022 study found that women with low egg maturity ratios are more likely to have reduced live birth rates.

Only mature eggs can be fertilized, and these eggs (sometimes called “M2” eggs) can be distinguished by the presence of a polar body. Not all eggs are mature after an egg retrieval, and it’s not clear if the egg maturity ratio has any impact on IVF outcomes.

For more background on egg quality and maturity, check out my Complete guide to egg quality.

Capper et al. (2022), in their retrospective study, compared egg maturity ratios and IVF outcomes in 1,451 cycles between 2016 and 2019 at a single IVF center in the USA.

Both ICSI and conventional IVF cycles were used, and all transfers were performed using blastocysts. To check for maturity, after retrieval the eggs were immediately placed under phase-contrast microscopy and the cumulus was spread to evaluate the egg. Eggs to be used for ICSI had their cumulus cells stripped after 6 hours and checked a second time.

Only autologous cycles were used (no donor eggs), and only the first embryo transfer was considered.

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Reduced clinical pregnancies and live births in women with low egg maturity

Women were grouped based on egg maturity ratios (high: >99.5% mature, average: 71.5-99.5% mature, below average: 57.5-71.4% mature or low: <57.5% mature).

Compared to women with average egg maturity ratios, women with low maturity ratios had a statistically significant reduced chance of clinical pregnancy (30.8% vs 56.4%) and live birth (28.8% vs 52.2%).

Live birth rates also seem to decrease in those with high maturity but this was not statistically significant. However, there was a statistically significant decrease when considering clinical pregnancies in high and average maturity groups (48.8% vs 56.4%). The authors were unclear as to why this is.

There were no differences in miscarriage or fertilization rates among the groups.

Certain clinical factors are associated with egg maturity ratios

Women who were anovulatory had a slightly reduced egg maturity ratio (81.9% vs 85.5%), while women with diminished ovarian reserve had a slightly higher ratio (87.8% vs 84.5%).

They found no statistically significant associations with egg maturity ratios and age, days of stimulation before trigger, the type of trigger used (GnRH, hCG or dual trigger) and the total amount of gonadotropins used.

Repeat low maturity ratios may occur in subsequent cycles

Women with egg maturity ratios <57.5% in their first cycle had a 34% chance of having a similar ratio in their second cycle. However, women with higher initial egg maturity ratios (>71.5%) had a 9% chance of having a second cycle with maturity ratios <57.5%.

Conclusions

This study found that women with low egg maturity ratios (<57.5% mature) had reduced clinical pregnancy and live birth rates. Some women with below average maturity ratios experienced a second cycle with similar ratios.

They also found that age, days of stimulation before trigger, the type of trigger used and the total amount of gonadotropins used had no impact on egg maturity ratios. The authors were surprised that a longer stimulation time didn’t have any effect on egg maturity, as many centers will prolong stimulation in an attempt to yield more mature eggs.

Reference

Capper E, Krohn M, Summers K, Mejia R, Sparks A, Van Voorhis BJ. Low oocyte maturity ratio is associated with a reduced in vitro fertilization and intracytoplasmic sperm injection live birth rate. Fertil Steril. 2022 Oct;118(4):680-687. doi: 10.1016/j.fertnstert.2022.07.008. Epub 2022 Sep 6. PMID: 36085173.

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.