Amino Acid Profiles in Dried Blood Spots and Clinical Outcomes in Selective Fetal Growth Restriction: A Twin-Pair Study

Selective fetal growth restriction (sFGR) remains a leading cause of perinatal morbidity in multiple pregnancies; however, its pathogenesis is not yet fully elucidated. Investigating amino acid metabolism in weight-discordant twins may uncover critical metabolic pathways involved in this condition, given the essential roles of amino acids in fetal growth and energy supply. The use of dried blood spots (DBSs) enables the minimally invasive, retrospective evaluation of neonatal metabolic profiles, providing a unique opportunity to identify sFGR-associated signature and clarify differences between monochorionic (MC) and dichorionic (DC) placentation. In the present study, we profiled 23 amino acids in DBS from 23 twin pairs (11 discordant and 12 non-discordant, defined by postnatal birth-weight discordance), stratified by chorionicity, to identify specific metabolic signatures associated with sFGR and to evaluate their temporal dynamics and clinical significance. Our findings suggest that chorionicity is associated with distinct amino acid signatures of postnatal birth-weight discordance. In MC twins, the larger co-twin displayed significantly elevated glycine, α- and γ-aminobutyric acids, serine, asparagine, and citrulline, alongside reduced proline and tryptophan. In DC twins, the larger co-twin exhibited higher α-aminobutyric acid, valine, leucine, arginine, and citrulline, whereas glycine was elevated in the smaller co-twin. Pathway enrichment analysis further suggested the enrichment of amino acid transport and protein synthesis pathways in MC postnatal discordance and nitric oxide (NO)-dependent signaling in DC postnatal discordance. Longitudinal follow-up showed a statistically significant attenuation of intrapair differences for several amino acids by the second time point. All 11 discordant pairs were retrospectively confirmed to fulfil the Delphi criteria for sFGR. These findings are exploratory and hypothesis-generating.