The study is the first to examine the effect of adolescent maternal nutrient intake on the development of fetal bone length during pregnancy. The researchers note that pregnant teens face dramatic nutritional demands because they have not achieved peak bone mass, and must simultaneously accrue bone and accommodate the skeletal development of their fetus. Competition for calcium between the teenage mom and her baby may influence fetal skeletal consolidation. "The femur is the longest and fastest growing bone in the fetus. Its length is typically measured during routine fetal sonograms and is a good indicator of overall bone development," said principal investigator Kimberly O'Brien, PhD, associate professor with CHN and the School's Department of International Health. "With more than one million teenage girls becoming pregnant in the United States each year and a half million of these pregnancies resulting in live births, this study could provide critical new data to help improve health in this at-risk population."
Shih-Chen Chang, a PhD candidate in the Department of International Health who conducted the retrospective cohort study for his doctoral thesis, analyzed extensive data on pregnant teens collected from the Maternity Center East Clinic between 1990 and 2000.
A registered dietician who worked at the clinic, which is affiliated with the Johns Hopkins Hospital, evaluated dietary intake for all girls who entered prenatal care. Using a 24-hour dietary recall to estimate the number of dairy products the girls consumed daily, the dietician ranked their calcium intake as either "adequate" (4 or more servings per day), "fair" (2-3 servings per day) or "poor" (0-1 serving per day), with each serving contributing approximately 300 milligrams of calcium. The study found that more than 75 percent of this Baltimore cohort consumed inadequate calcium. Since 1998, the Institute of Medicine has recommended that adolescents consume 1,300 milligrams of calcium daily. The recommendation is the same for pregnant adolescents, despite their increased nutritional demands, due in part to a scarcity of data on this population.
Among the Baltimore teens studied, they found that high maternal dairy intake at entry into prenatal care was associated with significantly greater fetal femur length. They also found that high dairy consumption was associated with better overall nutrition among these teen mothers. These mothers had significantly higher protein, vitamin A and iron intakes than those who consumed less dairy. Researchers also examined the effect of individual nutrients other than calcium on fetal femur length and found no significant relationship.
"This study showed that increasing dairy intake in this vulnerable population should have beneficial effects for the developing fetus," Dr. O'Brien explained. "It also shows that we need further studies to determine the long-term effect of nutrition during adolescent pregnancy on adolescent bone health, fetal femur development and bone density in the neonate at birth."
"Fetal femur length is influenced by maternal dairy intake in pregnant African American adolescents" was written by Shih-Chen Chang, Kimberly O'Brien, Maureen Schulman Nathanson, Laura E. Caulfield, Jeri Mancini and Frank R. Witter.
Funding for this research study was provided by National Institutes of Health/NICHD.
News releases from the Johns Hopkins Bloomberg School of Public Health are available at www.jhsph.edu/Press_Room.
Information about the Johns Hopkins Center for Human Nutrition is available at www.jhsph.edu/chn.
Journal
American Journal of Clinical Nutrition