Study population
We recruited 8 pregnant women between December 2011 to May 2012 using flyers placed in health centers, doctor's offices, and in public settings around Chapel Hill, North Carolina. Women provided demographic information and urine samples during pregnancy. In the 18th week of pregnancy each woman collected a 24-hour urine specimen as well as 2 first morning voids, approximately 48-hours apart. Women were also asked to provide a first morning void in the 28th week of pregnancy and a spot urine sample after their child's birth. All 8 women provided urine samples during the first 4 sample collection time points and 7 women provided urine samples after the birth of their child (samples collected 1 to 10 days post-birth). Our final sample consisted of 39 urine specimens. All study protocols were approved by the institutional review board at the University of North Carolina–Chapel Hill and all women provided informed consent.