Athens, Greece ? Being fat at one of three stages in your life may be critical in predicting whether you will have a weight problem as an adult, researchers said this week, citing several studies.

A person’s weight at birth, as a preschooler and as a teen seem to have a strong connection to weight problems in adulthood, said scientists at Europe’s annual conference on obesity research. If the evidence holds up, it could signal public health experts when to intervene.

In the case of infants, it will be hard to convince parents, and even nurses, to move away from the idea of aiming for a big baby, experts predict.

“They like to see them get high up on those (growth) curves, particularly in those early days. It’s pretty ingrained in the maternal and child health nursing system to have a big baby, and it’s probably not a smart idea,” said Dr. Boyd Swinburn, an obesity expert from Deakin University in Melbourne, Australia. “And this under-recognition by parents is huge. It’s going to be a major stumbling block.”

However, scientists don’t know exactly what weight is too big, nor is it clear just how much control a pregnant woman could have on the size of her developing fetus.

Studies have shown that babies who are born large are more likely to end up fat as adults. On the other hand, being born very small also seems to increase the risk of obesity in adulthood, especially if such infants are then fed intensively to allow rapid growth so they catch up with their peers.

“There are data from several different countries, including Israel, America, Europe and Southeast Asia” that demonstrate the birth weight effect, said Tim Lobstein, a childhood-obesity specialist at the International Obesity Task Force.

“The optimum is to try and have a baby around the 6 pounds or 7 pounds mark,” he said.

The next stage that may be important is the preschool period, research suggests. Several studies indicate that children who gain weight before gaining height between toddlerhood and elementary school seem to have a higher chance of being fat adults.

Rapid weight gain due to overfeeding in the first year of life may be particularly risky for later obesity, experts say.

Major studies over the last few years indicate that about one in three children who are fat in early childhood end up as overweight adults. Children who get fat before age 8 tend to end up more severely obese as adults than those who gain weight afterward.

But being fat in the teenage years seems to be even more predictive of later obesity, research indicates. About 70 percent of fat adolescents end up obese later in life.