title: A prospective longitudinal study of growth velocity in twin pregnancy.
abstract: OBJECTIVE
  Fundamental research into the growth of twins is lacking. Twin growth in utero is commonly assumed to follow similar patterns of growth as that of singletons. This preliminary descriptive study on twin pregnancy aimed to define growth velocity as gestation advances, and to study if twin order, fetal sex, zygosity and chorionicity have any relationship to growth velocity.
  
  
  METHODS
  One hundred and sixty-two women with twin pregnancies had an ultrasound examination at fortnightly intervals from 16 weeks until delivery. Fetal measurements of biparietal diameter, abdominal circumference and femur length were performed at each examination. Growth velocity for each parameter was defined as the difference in measurements for that parameter divided by the time interval between measurements. Postnatally, zygosity and chorionicity were determined by genetic fingerprinting and inspection of the placenta, respectively.
  
  
  RESULTS
  Growth velocity for all parameters decreased as gestation advanced, with the downward trend more noticeable after 32 weeks. Maximum and minimum growth occurred at 22-23 weeks and 36-37 weeks, respectively. Maximum and minimum growth velocities for the abdominal circumference were 1.7 and 0.8 cm/week, respectively. Birth order, fetal sex, chorionicity and zygosity were not related to growth velocity.
  
  
  CONCLUSIONS
  These preliminary results suggest that growth velocity in twins decreases after 32 weeks' gestation. It appears that growth velocity is independent of birth order, fetal sex, chorionicity and zygosity.
authors.affiliation: Aberdeen Maternity Hospital, Aberdeen, UK.
authors.forename: A P
authors.initials: AP
authors.lastname: Smith
authors.forename: S
authors.initials: S
authors.lastname: Ong
authors.forename: N C
authors.initials: NC
authors.lastname: Smith
authors.forename: D
authors.initials: D
authors.lastname: Campbell
mesh_terms: D000886:Anthropometry; D005314:Embryonic and Fetal Development; D005260:Female; D005333:Fetus / Q000033:anatomy & histology; D005865:Gestational Age; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000502:physiology*; D011446:Prospective Studies; D014427:Twins; D016216:Ultrasonography, Prenatal