[1] Baylor Coll Med, Dept Pediat, Sect Hematol Oncol, Houston, TX USA
[2] Univ Texas Hlth Sci Ctr Houston, Sch Publ Hlth, Houston, TX USA
[3] Baylor Coll Med, Dept Med, Sect Epidemiol & Populat Sci, Houston, TX USA
[4] Texas Dept State Hlth Serv, Birth Defects Epidemiol & Surveillance Branch, Environm Epidemiol & Dis Registries Sect, Austin, TX USA
[5] Baylor Coll Med, One Baylor Pl, MS BC M622, Houston, TX 77030 USA