A new study published in the Journal of Affective Disorders aimed to determine the relationship between plasma-tryptophan concentrations during pregnancy and sleep quality and mood, during and after pregnancy. In this study, pregnant women from the Growing Up in Singapore Towards Healthy Outcomes study completed the Pittsburgh Sleep Quality Index (PSQI), the Edinburgh Postnatal Depression Scale (EPDS), and the State-Trait Anxiety Inventory (STAI) at 26-28 weeks gestation and three months post-delivery. Plasma tryptophan concentrations were measured at 26-28 weeks gestation. The findings showed that the mean plasma tryptophan concentration was 48.0µmol/L (SD: 8.09). Higher plasma tryptophan concentrations were associated with a lower prevalence of antenatal poor sleep quality, especially in those who also suffered from anxiety symptoms. While no associations were observed between tryptophan concentrations during pregnancy and postnatal sleep quality or mental well-being. From the results, it was inferred that higher plasma tryptophan concentrations were associated with a 12% lower prevalence of poor sleep quality during pregnancy, specifically among those with anxiety symptoms. These findings emphasized the importance of having adequate tryptophan concentrations during pregnancy.