Conclusion
These findings suggest that prenatal anxiety is associated with low birthweight and short gestational age. This association was robust following consideration of controlling for shared family confounding, and exposure to alcohol and smoking during pregnancy. It is therefore important to consider maternal mental health during pregnancy, as these women may need extra psychological attention and support during prenatal care.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors declare that they have no conflict of interest.
The Author Contributions: MB developed the research question and prepared the first draft of the manuscript together with SO, YL, REB and PM. MB have been the main author of all sections of the paper, while REB has written the introduction. YL has conducted all analyses together with SO. All authors has contributed to the interpretation of the data and analyses for the work, and all authors revised the manuscript critically and approved the version to be published.
Ethical approval: The MoBa have approval from the committee for medical research ethics in 2009 (REK- 2009/1899-7), and 12th of October, 2016 (REK-2016/1424).
Funding : The Norwegian Mother, Father and Child Cohort Study is supported by the Norwegian Ministry of Health. This work was partly supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number 262700, and was also supported by the Research Council of Norway, NRC, grant nr 288083.
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