title: Comparison of multiple methods to measure maternal fat mass in late gestation.
abstract: BACKGROUND
  Measurements of maternal fat mass (FM) are important for studies of maternal and fetal health. Common methods of estimating FM have not been previously compared in pregnancy with measurements using more complete body composition models.
  
  
  OBJECTIVE
  The goal of this pilot study was to compare multiple methods that estimate FM, including 2-, 3- and 4-compartment models in pregnant women at term, and to determine how these measures compare with FM by dual-energy X-ray absorptiometry (DXA) 2 wk postpartum.
  
  
  METHODS
  Forty-one healthy pregnant women with prepregnancy body mass index (in kg/m(2)) 19 to 46 underwent skinfold thickness (SFT), bioelectrical impedance analysis (BIA), body density (Db) via air displacement plethysmography (ADP), and deuterium dilution of total body water (TBW) with and without adjustments for gestational age using van Raaij (VRJ) equations at 37-38 wk of gestation and 2 wk postpartum to derive 8 estimates of maternal FM. Deming regression analysis and Bland-Altman plots were used to compare methods of FM assessment.
  
  
  RESULTS
  Systematic differences in FM estimates were found. Methods for FM estimates from lowest to highest were 4-compartment, DXA, TBW(VRJ), 3-compartment, Db(VRJ), BIA, air displacement plethysmography body density, and SFT ranging from a mean ± SD of 29.5 ± 13.2 kg via 4-compartment to 39.1 ± 11.7 kg via SFT. Compared with postpartum DXA values, Deming regressions revealed no substantial departures from trend lines in maternal FM in late pregnancy for any of the methods. The 4-compartment method showed substantial negative (underestimating) constant bias, and the air displacement plethysmography body density and SFT methods showed positive (overestimating) constant bias. ADP via Db(VRJ)and 3-compartment methods had the highest precision; BIA had the lowest.
  
  
  CONCLUSIONS
  ADP that uses gestational age-specific equations may provide a reasonable and practical measurement of maternal FM across a spectrum of body weights in late pregnancy. SFT would be acceptable for use in larger studies. This trial was registered at clinicaltrials.gov as NCT02586714.
authors.affiliation: Oregon Health & Science University, Portland, OR; marshani@ohsu.edu.
authors.forename: Nicole E
authors.initials: NE
authors.lastname: Marshall
authors.affiliation: University of California, San Francisco, San Francisco, CA; and.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Murphy
authors.affiliation: Children's Hospital Oakland Research Institute, Oakland, CA.
authors.forename: Janet C
authors.initials: JC
authors.lastname: King
authors.affiliation: Oregon Health & Science University, Portland, OR;
authors.forename: E Kate
authors.initials: EK
authors.lastname: Haas
authors.affiliation: Oregon Health & Science University, Portland, OR;
authors.forename: Jeong Y
authors.initials: JY
authors.lastname: Lim
authors.affiliation: Oregon Health & Science University, Portland, OR;
authors.forename: Jack
authors.initials: J
authors.lastname: Wiedrick
authors.affiliation: Oregon Health & Science University, Portland, OR;
authors.forename: Kent L
authors.initials: KL
authors.lastname: Thornburg
authors.affiliation: Oregon Health & Science University, Portland, OR;
authors.forename: Jonathan Q
authors.initials: JQ
authors.lastname: Purnell
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000273:Adipose Tissue / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D001823:Body Composition; D015992:Body Mass Index; D001834:Body Water; D003903:Deuterium / Q000378:metabolism; D017097:Electric Impedance; D005240:Feasibility Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007201:Indicator Dilution Techniques; D016014:Linear Models; D010865:Pilot Projects; D010991:Plethysmography / Q000379:methods; D011247:Pregnancy; D011446:Prospective Studies; D012885:Skinfold Thickness; D055815:Young Adult
chemical_list: D003903:Deuterium
keywords: air displacement plethysmography; dual-energy X-ray absorptiometry; maternal body composition; maternal fat mass; maternal obesity; pregnancy; skinfold thickness; total body water