Background and aims 
The main aim of the study is to identify the primary trajectories of Body Mass Index (BMI) development. More speciﬁc, the aim is to identify the trajectories that may lead to overweight or obesity for children at later stages of life and which factors are affecting this abnormal growth.
Methods
The longitudinal data consists of growth measurements from 6906 Finnish children from six birth cohorts: 1974 (n=1108), 1981 (n=977), 1991 (n=586), 1995 (n=786), 2001 (n=765) and 2004 (n=2684). The anthropometric data was collected from birth up to age 15 in the health records as well as the pregnancy health data for birth cohorts 1991, 1995, 2001 and 2003-04. From 624 children in birth cohorts 1995 and 2001 lifestyle factors and other background determinants were collected.
A trajectory analysis was used to identify trajectories for BMI development. A trajectory analysis was used to identify trajectories for BMI development. Factors that lead to abnormal growth tracks were analyzed using using logistic regression models.
Results
Trajectory analysis identiﬁed four main trajectories of BMI growth. Two of these trajectories doesn’t seem to follow the normal growth pattern. The highest growth track appears to lead to overweight while the low growth track differs among the sexes. 
Pre-pregnancy BMI, gestational diabetes mellitus (GDM) and gestational weight gain (GWG) are associated with higher risk for overweight growth track.
Conclusion 
Trajectory analysis provides a powerful tool to analyse longitudinal data and the development of BMI. Study results suggest that primary prevention strategies for child obesity should start early by targeting maternal pre-pregnancy BMI and gestational weight gain.

Factors that predict abnormal growth