title: Placental weight mediates the effects of prenatal factors on fetal growth: the extent differs by preterm status.
abstract: OBJECTIVE
  Elevated pre-pregnancy BMI, excessive gestational weight gain (GWG), and gestational diabetes mellitus (GDM) are known determinants of fetal growth. The role of placental weight is unclear. We aimed to examine the extent to which placental weight mediates the associations of pre-pregnancy BMI, GWG, and GDM with birth weight-for-gestational age, and whether the relationships differ by preterm status.
  
  
  METHODS
  We examined 1,035 mother-infant pairs at birth from the Boston Birth Cohort. Data were collected by questionnaire and clinical measures. Placentas were weighed without membranes or umbilical cords. We performed sequential models excluding and including placental weight, stratified by preterm status.
  
  
  RESULTS
  We found that 21% of mothers were obese, 42% had excessive GWG, and 5% had GDM. Forty-one percent were preterm. Among term births, after adjustment for sex, gestational age, maternal age, race, parity, education, smoking, and stress during pregnancy, birth weight-for-gestational age z-score was 0.55 (0.30, 0.80) units higher for pre-pregnancy obesity vs. normal weight. It was 0.34 (0.13, 0.55) higher for excessive vs. adequate GWG, 0.67 (0.24, 1.10) for GDM vs. no DM, with additional adjustment for pre-pregnancy BMI. Adding placental weight to the models attenuated the estimates for pre-pregnancy obesity by 20%, excessive GWG by 32%, and GDM by 21%. Among preterm infants, GDM was associated with 0.67 (0.34, 1.00) higher birth weight-for-gestational age z-score, but pre-pregnancy obesity and excessive GWG were not. Attenuation by placental weight was 36% for GDM.
  
  
  CONCLUSIONS
  These results suggest that placental weight partially mediates the effects of pre-pregnancy obesity, GDM, and excessive GWG on fetal growth among term infants.
authors.affiliation: MOE-Shanghai Key Laboratory of Children's Environmental Health, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
authors.forename: Fengxiu
authors.initials: F
authors.lastname: Ouyang
authors.forename: Margaret
authors.initials: M
authors.lastname: Parker
authors.forename: Sandra
authors.initials: S
authors.lastname: Cerda
authors.forename: Colleen
authors.initials: C
authors.lastname: Pearson
authors.forename: Lingling
authors.initials: L
authors.lastname: Fu
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Gillman
authors.forename: Barry
authors.initials: B
authors.lastname: Zuckerman
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D015992:Body Mass Index; D001835:Body Weight; D001900:Boston / Q000453:epidemiology; D015331:Cohort Studies; D016640:Diabetes, Gestational / Q000453:epidemiology; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D009765:Obesity / Q000453:epidemiology*; D010298:Parity; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy; D012307:Risk Factors; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D055815:Young Adult