[1] Univ S Florida, Dept Obstet & Gynecol, Div Gen Obstet & Gynecol, Tampa, FL 33620 USA
[2] Univ N Carolina, Dept Obstet & Gynecol, Div Gen Obstet & Gynecol, Chapel Hill, NC 27515 USA
[3] Univ N Carolina, Dept Obstet & Gynecol, Div Maternal Fetal Med, Gillings Sch Global Publ Hlth, Chapel Hill, NC 27515 USA
[4] Univ N Carolina, Dept Maternal & Child Hlth, Gillings Sch Global Publ Hlth, Chapel Hill, NC 27515 USA