Funding for this research was provided by:
the National Natural Science Foundation of China (81571453; 81771607)
Article History
Received: 8 May 2019
Accepted: 30 October 2019
First Online: 11 November 2019
Ethics approval and consent to participate
: This study used data from the Chongqing National Population-Based Birth Defects Surveillance System. The patients whose data were included gave informed consents and agreed to the usage of their data for research.
: Not applicable.
: The authors declare that they have no competing interests.