Frozen Blastocyst Quality and Child Growth

A new study finds the microscopic quality of a frozen blastocyst does not predict a child's physical growth from birth to age five. The research, published in August 2026 in the journal Fertility and Sterility, followed 1,365 children born after single frozen blastocyst transfers.

Researchers from Asada Ladies Clinic and the Asada Institute for Reproductive Medicine in Japan conducted the analysis. They aimed to see if the morphological grade assigned to an embryo before freezing was linked to long-term health outcomes. The team reviewed data from children born between 2013 and 2018.

Study Design and Methods

The study was a retrospective cohort analysis. It included 1,365 singletons born from single frozen-thawed blastocyst transfers. Embryo quality was graded at the blastocyst stage using a standard system that evaluates expansion and the appearance of inner cell mass and trophectoderm cells.

Children's growth was measured using standard World Health Organization parameters. These included weight, height, and head circumference at birth and at routine check-ups up to five years old. The researchers then compared the growth trajectories of children from top-grade blastocysts with those from non-top-grade blastocysts.

Key Findings on Growth

The analysis revealed no significant differences in growth patterns. Children born from top-quality blastocysts grew at the same rate as those from lower-graded embryos. This held true across all measured parameters from infancy through early childhood.

The study's authors, led by Dr. Kazuma Onishi, state the findings are reassuring. They suggest that while blastocyst morphology is useful for selecting embryos with high implantation potential, it may not be a marker for postnatal physical development. The child's growth environment after birth appears to be far more influential.

Embryo Grading Categories

The blastocysts in the study were categorized by their expansion grade and cell quality. The following table outlines the grading system used, as described in the source research.

This grading was performed prior to the vitrification freezing process. All embryos were transferred in single-embryo transfer cycles to avoid the confounding effects of multiple births.

The research provides evidence for patients considering frozen embryo transfer. It indicates that using a non-top-graded blastocyst does not condemn a child to poorer growth. The study did not investigate other developmental outcomes like neurodevelopment or metabolic health. The authors note that further research is needed to explore those areas. The final data point shows consistent growth curves, regardless of the embryo's starting grade.