Effect of predominant breastfeeding duration on infant growth: a prospective study using nonlinear mixed effect models.
OBJECTIVE
The aim of this study is to assess the effect of predominant breastfeeding duration on infant growth by means of repeated measurements model.


METHODS
This prospective study is comprised of four follow-up evaluations at approximately 0.5, 2, 6 and 9 months after birth, including structured interviews that simultaneously gathered information regarding infant growth and breastfeeding practices. The study took place in a healthcare center in Rio de Janeiro, Brazil, from 1999 to 2001. Four hundred seventy-nine postpartum women and their newborns were enrolled in the cohort. Body weight and length measurements taken at five different occasions (birth, 0.5, 2, 6, and 9 months) constituted the dependent variables. We expressed the growth process using nonlinear mixed models.


RESULTS
Infants with longer predominant breastfeeding duration, although growing faster in the first months of life, reached an inferior equilibrium body weight and length compared to infants who received nonhuman milk earlier in life. The age at which the rate of weight gain of the formula-fed infants becomes greater than that of the breastfed infants is approximately 6.75 months for boys and 7 months for girls.


CONCLUSIONS
This study confirms the differences observed in infant growth according to different breastfeeding practices starting from the sixth month of life. Use of nonlinear models allowed for a greater precision of parameter estimates. We believe that this approach facilitates the analysis and interpretation of growth data at the individual and population levels.
Departamento de Estatística, Universidade Federal do Rio Grande do Norte, Natal, RN.
Maria Helena Constantino
MH
Spyrides
Cláudio José
CJ
Struchiner
Maria Tereza Serrano
MT
Barbosa
Gilberto
G
Kac
D000293:Adolescent; D000328:Adult; D001942:Breast Feeding / Q000706:statistics & numerical data*; D002657:Child Development / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006128:Growth / Q000502:physiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007407:Interviews as Topic; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D011446:Prospective Studies; D013997:Time Factors