title: Human embryonic growth trajectories and associations with fetal growth and birthweight.
abstract: OBJECTIVE
  How do human embryonic growth trajectories evolve in the first trimester, and is first-trimester embryonic growth associated with fetal growth and birthweight (BW)?
  
  
  CONCLUSIONS
  Human embryonic growth rates increase between 9 and 10 weeks of gestation and are associated with mid-pregnancy fetal growth and BW.
  
  
  BACKGROUND
  Fetal growth is associated with health and disease risks in later life. Until recently, prenatal care and research have been focused predominantly on fetal growth in the second and third trimesters of pregnancy. Longitudinal first-trimester data remain scarce.
  
  
  METHODS
  We recruited 201 pregnancies before 8 weeks of gestation in a prospective periconception cohort study conducted in a tertiary center.
  
  
  METHODS
  We performed weekly 3D ultrasound scans from enrollment up to 13 weeks of gestation. To create embryonic growth trajectories, serial crown-rump length (CRL) measurements were performed using the V-Scope software in the BARCO I-Space. Mid-pregnancy fetal growth parameters and BW were obtained from medical records. Z-scores were calculated for CRL, mid-pregnancy estimated fetal weight (EFW) and BW. Associations between embryonic and fetal growth parameters were investigated using Pearson's correlation coefficients.
  
  
  RESULTS
  During the early first trimester (up to 9 weeks of gestation), we observed a constant absolute mean embryonic CRL growth rate of 0.99 mm/day (SD 0.10), while the relative growth rate decreased. Between 9 and 10 weeks of gestation, the absolute growth rate increased, and during late first trimester (from 10 weeks of gestation onward), we observed a constant mean relative growth rate of 4.1% (SD 0.006) per day. Overall, early and late first-trimester median CRL Z-scores were strongly correlated with mid-pregnancy EFW (r overall/early/late = 0.57/0.57/0.54, P < 0.001) but only overall and late CRL Z-scores were correlated with BW (r overall = 0.15, P = 0.04; r early = 0.10, P = 0.17; r late = 0.17, P = 0.02).
  
  
  CONCLUSIONS
  This study was conducted in a tertiary hospital. Therefore, future studies in other populations are warranted to confirm our results.
  
  
  CONCLUSIONS
  This study shows differences between early and late first-trimester embryonic growth coinciding with changes in intrauterine nourishment. The established associations between first-trimester embryonic growth and fetal size in mid-pregnancy and at birth emphasize that more research is warranted to establish the importance of these results for preconceptional and early pregnancy care.
authors.affiliation: Department of Obstetrics and Gynaecology, Erasmus MC, University Medical Centre, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands.
authors.forename: Evelyne M
authors.initials: EM
authors.lastname: van Uitert
authors.forename: Niek
authors.initials: N
authors.lastname: Exalto
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Burton
authors.forename: Sten P
authors.initials: SP
authors.lastname: Willemsen
authors.forename: Anton H J
authors.initials: AH
authors.lastname: Koning
authors.forename: Paul H C
authors.initials: PH
authors.lastname: Eilers
authors.forename: Joop S E
authors.initials: JS
authors.lastname: Laven
authors.forename: Eric A P
authors.initials: EA
authors.lastname: Steegers
authors.forename: Régine P M
authors.initials: RP
authors.lastname: Steegers-Theunissen
mesh_terms: D000328:Adult; D001724:Birth Weight; D015331:Cohort Studies; D047108:Embryonic Development; D005260:Female; D047109:Fetal Development; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011295:Prenatal Care; D016216:Ultrasonography, Prenatal
keywords: 3D imaging; crown–rump length; embryonic development; first trimester; pregnancy