The authors analyzed data on mothers' recalled weights and weight gain for more than 24,000 mother-daughter pairs. The heavier a mother was before her pregnancy, the more likely her daughter was to be obese in later life. For instance, an average-height mother who weighed 150 pounds before pregnancy was twice as likely to have a daughter who was obese at age 18 as a mother who weighed 125 pounds before pregnancy.

Weight gain during pregnancy mattered, too - both too little and too much weight gain increased a daughter's risk of becoming obese, especially if a mother was overweight before she got pregnant.

Using the Nurses' Health Study II, the authors analyzed data for more than 24,000 mother-daughter pairs. The daughters, all registered nurses, are part of the Nurses' Health Study. They reported their weight at age 18 when they joined the study in 1989, and they reported their current weight in 2001.

In 2001, each mother was asked to recall her pre-pregnancy height and weight, her weight gain while she was pregnant with her daughter, and her daughters' weight at birth.

Daughters whose mothers gained 15 to 19 pounds during pregnancy had the lowest risk of obesity. Compared to this group, daughters whose mothers gained more than 40 pounds while pregnant were almost twice as likely to be obese at age 18 and later in life.

Too little weight gain was also linked with a daughter's obesity risk. Pregnancy weight gain of fewer than 10 pounds was associated with a 1.5-fold increase in the odds of being obese at 18 and a 1.3-fold increase in odds of being obese in later life.

The study was published June 16, 2009, in the online version of the International Journal of Obesity.