Initial and doubling beta-hCG linked to embryo development and quality

A 2024 study found that beta-hCG levels were related to day 3 and day 5 embryo quality and development, with blastocyst expansion having the strongest impact on both initial beta values and their doubling.

Beta-hCG (or simply “beta”) is a hormone secreted by early placental cells after the embryo implants. It’s often referred to as the pregnancy hormone and is measured by a blood test about 12-16 days after embryo transfer as a way to detect pregnancy.

Beta-hCG levels can be tested a second time to measure how the hormone is doubling. The initial beta and how it changes with a second measurement is important information to confirm early pregnancy.

It’s not clear how these beta values change with day 3 or day 5 transfers, and whether or not the quality of the embryo can predict these values.

You can learn more about embryo grading in my Complete Guide to Embryo Grading and Success Rates.

This post is a summary of a study by Chu et al. (2024), who related embryo grades to the initial beta value on day 14, and how it doubled on day 18, after a single day 3 or day 5 embryo was transferred. All the women in this study had a positive beta-hCG from the transfer, and they just wanted to see how embryo grades influenced these beta-hCG values.

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Study details

This section covers key details of how the study was performed, including patient characteristics, how they were treated, and other methods used. For those who aren’t interested in these details, and just want to see the results, you can go ahead and skip this part.

• This is a retrospective study that took place at a single IVF center in China between 2016 and 2020.
• Inclusions/exclusions: Only patients who transferred a single fresh day 3 or day 5 embryo, with a beta of 50 mIU/ml recorded 14 days after transfer were included. No PGT.
• Day 5 embryos were graded by the Gardner system (3AA, 5BC, etc.). Day 3 embryos were graded based on the ASEBIR system. In terms of fragmentation %. Grade I: <10% fragmentation; Grade II: 10-25% fragmentation; Grade III: >25% fragmentation.
• Blood was drawn on day 14 for the beta measurement and again on day 18 for doubling measurements.

In terms of sample size, there were 4434 positive beta-hCG pregnancies (measured on day 14): 1084 from a single day 3 embryo transfer, and 3350 from a single day 5 embryo transfer. There were 2628 doubling values measured on day 18: 628 from day 3 transfers and 2000 from day 5 transfers. In terms of embryo grades for the initial beta measurement:

• About 95% of the day 3 embryos were Grade II quality (10-25% fragmentation), and about 90% had 7-9 cells, 5% had 6 or fewer cells and 5% with 10 or more.
• About 98% of the day 5 embryos had an expansion of 3 or 4. For ICM grades, no blasts had a C grade ICM, but about 30% had an A grade and 70% had a B grade. For trophectoderm grades, about 10% had an A grade, 70% had a B grade and 20% had a C grade.

Day 3 embryo grade and day 14 beta-hCG levels are linked

The first thing the researchers did was a univariate and multivariate regression analysis to understand the relationship between beta-hCG levels and other variables, like age, day 3 embryo grades, BMI, etc. After this test, they found that day 3 embryo cell number and quality grade (by fragmentation %) were important predictors for beta-hCG levels (p= 0.013 and p= 0.047 for the multivariate analysis).

Next, they looked at the average beta-hCG levels 14 days after transferring a single day 3 embryo, based on cell number and quality.

Beta-hCG levels were highest on day 14 for day 3 embryos with 10 or more cells (448.74 mIU/ml). Embryos with less than 10 cells produced beta-hCG values between 318.15-361.41 mIU/ml on day 14. There was a statistical difference between 10 or more cells and <10 cells (lowest p= was 0.001, highest was p= 0.025), and between 7 and 8 cells (p= 0.049), but not between the other groups. This shows that more progressed embryos with 10 or more cells likely implant sooner and start building up beta-hCG levels.

For day 3 embryo quality, they looked at Grade I (<10% fragmentation), Grade II (10-25% fragmentation), and Grade III (>25% fragmentation). Transfer of a single day 3 embryo with <10% fragmentation or 10-25% fragmentation produced the highest beta-hCG values on day 14 (400.5 and 355.78 mIU/ml), compared to embryos with >25% fragmentation (202.41 mIU/ml), which was statistically significant (p= 0.007 and 0.012). There was no difference between <10% fragmentation and 10-25%. This shows that higher quality day 3 embryos are able to produce more beta-hCG than lower quality embryos.

Day 5 embryo grade and day 14 beta-hCG levels are linked

Again, the researchers did a univariate and multivariate regression analysis to understand the relationship between beta-hCG levels and other variables, like age, day 5 embryo grades, BMI, etc. After this test, they found that blastocyst expansion, inner cell mass grade and trophectoderm grade were important predictors for beta-hCG levels (p< 0.001, p= 0.014, p= 0.003 for the multivariate analysis).

Blastocyst expansion refers to how developed a blastocyst is. It goes from 1-6 and is the number portion of the blastocyst grade. In this study, they only transferred blastocysts with expansion 3-6.

The highest beta-hCG on day 14 was produced when a single day 5 blastocyst with an expansion of 4 or 5 was transferred (904.63 mIU/ml, 885.95 mIU/ml). Beta-hCG for expansion 3 was lower than 4 or 5, but there was no difference between 4 and 5. This was statistically significant (p< 0.001 and p= 0.040). Expansion 6 was also lower, but there was a very low sample size for this (only 3 transfers) so it probably isn’t representative. This shows that more advanced blastocysts likely implant sooner to produce more beta-hCG that accumulates by day 14.

They also compared the quality of the ICM and trophectoderm with beta-hCG values. An A grade ICM produced a higher beta-hCG on day 14 vs a B grade ICM (942.43 vs 826.46 mIU/ml, p< 0.001). There were no C grade ICM embryos in this study. Both A and B grade trophectoderms produced a similar beta-hCG on day 14 (904.82 and 900.57 mIU/ml), which was higher than a C grade trophectoderm (727.34). This was statistically significant (p< 0.001). This shows that higher quality ICM and trophectoderm could lead to higher production of beta-hCG.

They also provided values for specific blastocyst grades:

• 3BB: 766.25 mIU/ml
• 4BB: 903.86 mIU/ml
• 5BB: 947.02 mIU/ml
• 6BB: 1457 mIU/ml
• 3BC: 641.40 mIU/ml
• 4BC: 785.71 mIU/ml
• 5BC: 606.26 mIU/ml
• 4BA: 987.49 mIU/ml
• 3BA: 928 mIU/ml
• 4BA: 902.94 mIU/ml

Doubling beta-hCG values related to day 5 expansion, not day 3 quality

They also looked at how embryo quality related to beta-hCG doubling on day 18. Day 3 or day 5 embryo quality wasn’t linked to doubling, but day 5 expansion was. Expansion 3 had a higher doubling value compared to expansion 4 (4.814 vs 4.633, p= 0.033).

This seems weird because a more developed blastocyst had a lower doubling value. The authors explain that more expanded blastocysts might start off strong, with higher initial beta-hCG levels that don’t increase as dramatically later on. With less expanded blastocysts, they might try to “catch up” and show quicker increases in hormone levels as they develop.

The authors also explain that by day 18, factors other than just the embryo’s initial quality and development (like how well the placenta is functioning, the mother’s uterine environment, blood flow, and hormonal support) start influencing the hormone levels significantly. These factors can dilute the impact of embryo quality and development on hormone doubling rates.

Conclusions

Since all the beta measurements were done on day 14, regardless of a day 3 or day 5 transfer, the day 5 blastocysts produced higher levels of beta-hCG because they had a head start compared to the day 3s.

For day 3 transfers, higher quality embryos or 10 or more cells resulted in a higher beta-hCG on day 14. 

For day 5 blastocysts, higher quality or a higher blastocyst expansion also resulted in a higher beta-hCG on day 14.

Of all the factors examined in this study, the authors note that blastocyst expansion was most strongly linked to day 14 beta-hCG values.

This suggests that more developed embryos implant sooner to produce more beta-hCG that accumulates by day 14. The data also suggests that better quality embryos are able to produce more beta-hCG compared to lower quality embryos.

They also looked at how embryo quality related to beta-hCG doubling on day 18. Day 3 or day 5 embryo quality wasn’t linked to doubling, but day 5 expansion was. Expansion 3 had a higher doubling value compared to expansion 4, possibly due to more expanded blastocysts not producing beta-hCG as quickly as less expanded blastocysts.

Related studies

To learn more about this topic, you can check out a number of studies referenced in this study below (3 links):

Reference

Chu, Junting, Shanyue Guan, Ruonan Ma, Xiangyang Zhang, Song Ning, Wenyan Song, Guidong Yao, Senlin Shi, and Haixia Jin. 2024. “Relationship between Fresh Single Embryo Morphology Scores and Serum HCG Values at 14 Days and 14–18-Day Doubling Values.” Reproductive BioMedicine Online 49 (5): 104325.

 

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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.

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