A 2025 study of single-blastocyst transfers found no increase in birth defects or adverse pregnancy outcomes when transferring poor quality embryos compared to good quality ones.
Transferring C-graded embryos can be a difficult choice, especially when higher-grade ones aren’t available.
While embryo grading helps predict pregnancy rates, it’s not clear if there’s any relationship with birth defects (congenital malformations). Previous studies have shown mixed results, but these can be limited by small sample sizes or inconsistent grading criteria.
To clarify whether embryo quality is linked to birth defect risk, Du et al. (2025) examined outcomes of singleton births following frozen embryo transfer.
🔗 Original studies are referenced in this post or within the linked Remembryo posts.
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Study details
- Study type: Retrospective cohort study that took place between 2014 and 2023 at a single IVF center in China.
- Participants: 3,986 first, single-blastocyst FET cycles leading to singleton live births, including 3,023 good quality embryos and 963 poor quality embryos. After propensity score matching, these groups were reduced to 1,162 and 581. After matching, the average maternal age was about 32.
- Exclusions: No donor gametes, PGT-A cycles or patients with chromosomal abnormalities, endometriosis, Müllerian anomalies, diabetes, or thyroid disorders.
- Embryo grading: Gardner system; “good quality” = ≥3BB on day 5 or ≥4BB on day 6 (about 90% were day 5). All others were considered “poor quality,” mostly those with a C grade for the ICM or trophectoderm.
- Primary outcome: Congenital malformations.
- Statistical adjustment: Propensity score matching and multivariate logistic regression were used to minimize confounding, adjusting for maternal age, BMI, infertility type, fertilization method (IVF or ICSI), endometrial preparation protocol, embryo development day (Day 5 or 6), and parity.
No increased risk of birth defects with poor quality embryos
They found no differences in the rate of birth defects for good quality vs poor quality embryos (1.72% vs 2.07%, adjusted odds ratio [95% CI]: 1.14 [0.54–2.41], p= 0.73).
This was based on 15 ICD-10 codes (Q00–Q99), representing a range of congenital malformations such as heart defects (Q21), spina bifida (Q05), cleft palate (Q37), digestive system anomalies (Q42–Q43), limb or musculoskeletal defects (Q79), and chromosomal abnormalities (Q90, Q99).
They found no differences in any of these categories, and birth defects in each category were rare (<1%).
No differences in adverse pregnancy outcomes with poor quality embryos
They found no differences in:
- Neonatal outcomes: including gestational age at birth, preterm birth, birthweight and length, sex, congenital malformations, birthweight categories (very low, low, and high), size-for-gestational-age classifications (very small, small, large, and very large), NICU admission, and stillbirth.
- Obstetric complications: including gestational hypertension, gestational diabetes, fetal distress, amniotic fluid abnormalities, premature rupture of membranes, placenta previa, placental implantation disease, placental abruption, and cervical insufficiency.
- Cesarean delivery.
Conclusions
In this large study, researchers showed that there’s no increased risk of birth defects with poor vs good quality blastocysts.
They also found no differences in a number of adverse pregnancy and birth outcomes, like preterm birth, birthweight, gestational hypertension and gestational diabetes.
There are very limited data on this topic, and large numbers of births are needed to detect rare birth defects, making it hard to draw conclusions.
A larger 2019 study reported a modest increase in congenital malformations from poor-quality day 5 embryos, particularly musculoskeletal and chromosomal anomalies. The authors of the current study noted limitations in that earlier work, including a less standardized grading system and the inclusion of twin births, which may have introduced bias. Other smaller studies have found no link between embryo grade and birth defects, so results remain mixed. It’s possible that the increased risk of aneuploidy in poor quality embryos is related to this, but it’s not clear.
High-quality, large-scale studies are still needed to better understand how embryo grading relates to birth outcomes.
Limitations: Single-center design, possible unmeasured confounders not accounted for in propensity score matching, lack of long-term follow-up beyond infancy, and a larger sample size may be needed to account for rarer birth defects.
Want to read more about poor quality embryos?
This post takes a closer look at what “poor-quality” embryos really mean in IVF. At the cleavage stage, they often have fewer cells or high fragmentation, while at the blastocyst stage, a grade C means the inner cell mass and trophectoderm contain fewer, loosely packed cells. These embryos tend to have lower success rates than good-quality ones, but studies show they can have similar perinatal outcomes. Read more.
Researchers in a 2023 study show that poor quality embryos have acceptable live birth rates compared to good and fair quality embryos, with only a slight increase in pregnancy loss and no differences in perinatal outcomes. Read more.
A 2025 study found that while poor quality blastocysts are less likely to be euploid, some can still lead to healthy live births. Tested poor quality embryos had higher live birth rates and lower miscarriage rates than untested ones, especially when they developed by day 5 instead of day 6. Read more.
Related studies
These additional studies were referenced by the authors of the paper and haven’t been covered on Remembryo. They may be helpful if you’re exploring this topic further. This section is available for paid subscribers.
Reference
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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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