Childhood obesity doesn’t start in elementary school — it often begins much earlier, sometimes even before a child is born. A new study published in JAMA Network Open reinforces what health experts have long suspected: Prenatal and early-life conditions significantly shape a child’s risk for obesity later in life. These findings emphasize the importance of early intervention to encourage healthy growth patterns from the very start.
Early clues to a long-term problem
The study analyzed data from nearly 9,500 children between the ages of 1 and 9, tracking more than 53,000 BMI (body mass index) measurements. Researchers used a sophisticated modeling approach to uncover how BMI changes over time, not just whether a child is overweight at a certain age, but how and when those changes occur.
Children were categorized into two groups: those with a “typical” BMI pattern and those with an “atypical” trajectory — a group at higher risk for long-term obesity.
In a typical pattern (89% of children), BMI rose in infancy, dropped to its lowest point around age 6, then steadily increased through age 9 — a process known as adiposity rebound. In an atypical pattern (11% of children), these kids had stable BMIs from ages 1 to 3.5, followed by a steep increase through age 9. By age 9, their average BMI reached 26.2 — well above the 99th percentile.
The researchers noted that the timing of adiposity rebound is crucial. When this rebound happens earlier than normal, it’s considered a red flag for accelerated growth and increased risk of obesity and cardiometabolic conditions later in life.
Risk factors start before birth
The study also explored what environmental and biological factors were most predictive of a child following an atypical BMI trajectory. Several key prenatal and birth-related factors stood out:
- High maternal BMI before or during pregnancy
- Excessive weight gain during pregnancy
- Smoking during pregnancy
- High birth weight
- Preterm birth
Each of these increased the odds of a child ending up in the high-risk BMI group.
What’s happening inside the womb can also influence a child’s long-term health in less obvious ways. For example, maternal obesity and weight gain have been linked to disturbances in the development of the infant’s gut microbiome — the ecosystem of bacteria that affects digestion, metabolism, and immune response. A separate study in Clinical and Experimental Pediatrics found that children born to mothers with high BMIs were more likely to have microbiota profiles associated with obesity by the time they turned one, especially if delivered via cesarean section.
Why this study stands out
Most past research could only offer snapshots — a child’s weight at one age, compared with a benchmark. What makes this new study different is the ability to chart the shape of growth over time and detect deviations from normal development earlier than ever.
The researchers used a novel modeling technique called multiphase latent growth mixture modeling, which captures not just the amount of weight gain, but its timing and rate of change. While the method is more complex and computationally demanding, it provides a clearer, more personalized picture of how and when a child might be veering off a healthy growth path.
A call for early action
The key takeaway? Obesity prevention may need to start far earlier than preschool. By understanding the early-life factors that shape growth trajectories, parents and healthcare providers have an opportunity to intervene during critical windows, even before birth.
Whether it’s supporting maternal nutrition and prenatal care, encouraging breastfeeding, promoting gut health, or simply monitoring weight gain more closely during early childhood, the message is clear: The earlier we address the risk factors, the better the long-term outcomes for children.
As the authors concluded:
We identified modifiable early-life factors that may place children at risk for or protect children from childhood obesity.
What can parents do?
Here are some actionable steps to reduce the risk of early-onset obesity:
- Maintain a healthy weight during pregnancy. Work with a healthcare provider to stay within recommended gestational weight gain guidelines.
- Avoid smoking during pregnancy. It’s a known risk factor for various childhood health problems, including obesity.
- Encourage breastfeeding. It can support a healthy gut microbiome and reduce obesity risk.
- Watch for early signs of rapid weight gain. Regular pediatric visits with growth monitoring are essential.
- Support a healthy diet and active lifestyle from the start. Good habits formed early are more likely to stick.
While genetics and lifestyle are part of the equation, this study reminds us that environmental and prenatal factors play a powerful role. The good news? Many of those factors are modifiable. With greater awareness and proactive care (starting before birth), families and communities can help change the trajectory for the next generation.
Your responses and feedback are welcome!
Source: “Prenatal and Early-Life Contributors to Childhood and Adolescent Obesity,” The American Journal of Managed Care, 7/10/25
Source: “Early-Life Factors and Body Mass Index Trajectories Among Children in the ECHO Cohort,” JAMA Network Open, 5/22/25
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