we tanner stage pubic hair. if it's a boy, we actually measure testicular volume.the end of the visit, we can decide what if any tests are needed. >> so this is part of the camera, and i'm gonna bring the camera over, and this is what's going to take your picture. >> the first test that i find most useful is the skeletal maturation, which is a film of the wrist to the tip of the fingers called a bone age x-ray. skeletal maturation will show an advancement over the chronological age in a kid who has a true rise of the hormones. >> and then the second thing typically involves blood tests, and here we're measuring hormone levels. and the most important one in terms of evaluating puberty is called lh, or latinizing hormone. this is a hormone produced by the pituitary gland that stimulates the ovaries. then the last thing that the child undergoes would be a brain mri scan. and here we are looking specifically at the hypothalamus and the pituitary to make sure that there's no structural abnormality. >> mcfarland: joshua kellogg underwent a bone age x-ray that revealed hi

study, at age 7, 15% of girls had breast development and 10% of girls were developing hair already, pubic hairby age 8, which used to be the lower limit of normal, it was a much higher rate with 27% of the girls having breast development and about 19% having hair. >> so i know that that is alarming to a lot of families who aren't used to this. it kind of changes our brains. we have to think about this differently. so in your study, i know it's a long-term study, it's been going on for years. what are you learning so far. what are some of the triggers do you think? >> we are looking at a lot of different things. so the things that we're examining are environmental or chemical determinants that may promote early puberty. so for example, we are looking at nutrition, including breastfeeding. our girls at kaiser were girls that were born within keiser. we're able to lock at what kind of feeding their mothers were able to do. and then moving on to asking questions about what they eat on a regular basis now. so we're looking at nutrition. we're looking at location of homes. is your home next to a fre