Funding for this research was provided by:
National Institute of Environmental Health Sciences (Z1AES103325-01)
Maternal and Child Health Bureau, Health Resources and Services Administration, US Department of Health and Human Services (T71-MC-00009, T76-MC-00001)
Received: 6 October 2017
Accepted: 22 November 2017
First Online: 19 December 2017
Ethics approval and consent to participate
: Written informed consent was obtained from all study participants, and the National Institute of Environmental Health Sciences Institutional Review Board’s need for approval was considered waived for our analysis of publicly-available, secondary data.
: Not applicable.
: The authors declare that they have no competing interests.
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