title: Racial and ethnic disparity in male preterm singleton birth.
abstract: OBJECTIVE
  To evaluate the association between male sex and increased preterm birth (PTB) by race and ethnicity among singleton fetuses born in the United States.
  
  
  METHODS
  The 2002 National Center for Health Statistics Natality database was analyzed for known risk factors of PTB by fetal sex and race. Multivariable Cox proportional hazards regression was applied to estimate the hazard ratio by fetal sex for births between 20 and 36 completed gestational weeks. The multivariable model was adjusted for known demographic, medical and obstetric risk factors for PTB. Subgroup analysis was performed using both race and ethnicity.
  
  
  RESULTS
  In the overall analysis 3,853,678 singleton live births were included. PTBs between 20 and 36 completed weeks occurred in 10.9% of male and 9.8% of female infants. The association between PTB and male sex persisted after adjustment for other risk factors and did not vary by gestational age (hazard ratio [HR] 1.13, 95% CI 1.12-1.14). This association was seen in all racial and ethnic groups. This effect was less prominent among black infants (HR 1.06, 95% CI 1.04-1.07). Male fetuses with Hispanic ethnicity had a significantly higher risk of preterm birth (HR 1.15, 95% CI 1.13-1.17) compared to male fetuses of non-Hispanic ethnicity (HR 1.12, 95% CI 1.12-1.13).
  
  
  CONCLUSIONS
  In the U.S. male fetuses are at higher risk for PTB compared with female fetuses at the same gestational age. The etiology of this difference is unclear, but the effect is reduced for black compared to white fetuses and increased for Hispanic fetuses.
authors.affiliation: Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Women & Infants' Hospital of Rhode Island, Providence, RI 02905, USA. echien@wihri.org
authors.forename: Edward K
authors.initials: EK
authors.lastname: Chien
authors.forename: Asha
authors.initials: A
authors.lastname: Jayakrishnan
authors.forename: Tanya L
authors.initials: TL
authors.lastname: Dailey
authors.forename: Christina A
authors.initials: CA
authors.lastname: Raker
authors.forename: Maureen G
authors.initials: MG
authors.lastname: Phipps
mesh_terms: D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data; D001724:Birth Weight; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D005865:Gestational Age; D006630:Hispanic or Latino / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology* / Q000208:ethnology*; D016016:Proportional Hazards Models; D012307:Risk Factors; D012737:Sex Factors; D014481:United States / Q000453:epidemiology; D044465:White People / Q000706:statistics & numerical data