Funding for this research was provided by:
California Preterm Birth Initiative, UCSF
Received: 1 July 2019
Accepted: 15 November 2019
First Online: 2 December 2019
Ethics approval and consent to participate
: The study has been approved by the following ethics committees: University of California, San Francisco (16–19542), Benioff Children’s Hospital Oakland (2017–013), Community Regional Medical Center (2017096), and Kaiser Permanente (00001045). All participants will give written informed consent to participate in this study.
: Not applicable.
: The authors declare that they have no competing interests.