● Observed data

Between different embryos

Heteroplasmy levels in embryos, by mtDNA variant and source

Each point represents a published or derived heteroplasmy value for one embryo. Hollow markers indicate derived values. Diamonds indicate 1PN/3PN embryos, which are not candidates for transfer. Within each variant, separate columns show the sources.

Key finding. The proportion of embryos with heteroplasmy at or below 18% varies widely between variants: m.8993T>G — 24 of 26; m.3243A>G — 41 of 88; m.14487T>C — 6 of 28; m.3697G>A — 1 of 20. These proportions describe published series; they do not estimate the probability for an individual family.

Select a point to view its source and provenance. hollow marker — value calculated by averaging or digitised from a published figure.

Background bands: up to 18%, pale green; 18–30%, pale blue; 30–100%, pale red. The 18% reference point was estimated from muscle measurements (Hellebrekers et al., 2012); it is not a threshold for an embryo biopsy sample. The Newcastle programme predominantly used <30% (Hyslop et al., 2025). Proportions include values ≤ the selected boundary. These are not universal clinical thresholds.

Only intervals were published for two m.10197G>A embryos. They are shown as bars; no midpoint is imputed. An interval is included in the proportion ≤ the cut-off only when its upper bound is at or below that cut-off.