Strengths and limitations
The main limitation of this study is the small sample size; it is likely that higher sample sizes may have led to the conclusion that both trait anxiety and state anxiety are associated with lower birth weight percentiles. Nevertheless, this study was designed around specific stressful circumstances, during the COVID-19 pandemic lockdown, which represented an ideal scenario for investigating the effects of anxiety on birth weight, despite the reduced sample size. Another limitation of this study may be the selection bias due to including different anxiety symptoms according to the trimester of pregnancy. However, in a previous study conducted by our group, no statistically significant differences were found when analyzing STAIs and STAIt scores according to trimester of pregnancy. Finally, anxiety cannot be induced in an experimental research setting for ethical reasons. Therefore, the fact that this study included patients that were exposed to stressful circumstances in real life is the major strength of the present study.