THURSDAY, Jan. 30, 2003 (HealthDayNews) -- The length and head size of a baby girl when she is born can affect the risk that she will have breast cancer decades later, a European study indicates.
Looking through the many years of data about the more than 5,000 women born at the Uppsala Academic Hospital in Sweden between 1915 and 1929, British researchers say breast cancer was at least three times more likely to occur in longer babies with bigger heads, especially if their time in the womb was short.
Girl babies weighing more than 4,000 grams (8.8 pounds) were 3.5 times more likely to have breast cancer than those weighing less than 3,000 grams at birth, says a report in this week's issue of the British Medical Journal by researchers at the London School of Hygiene and Tropical Medicine. However, the increased risk was concentrated in the longest babies with the largest heads, the report says.
And gestation time also predicted risk, the researchers say. Babies born after less than 39 weeks in the womb were three times more likely to have breast cancer in their adult years as babies of the same size who spent more than 41 weeks in the womb. "Fetal growth rate, rather than size at birth alone, may be the etiological (causal) factor," they write.
The increased risk was found only in women who had breast cancer before menopause, they say.
How could size and length of pregnancy time affect breast cancer risk after may years? One theory is based on the knowledge that the mammary gland starts to develop before birth, they say. Exposure to high concentrations of growth factor might result in development of cells that are likely to turn cancerous over the years, they say. And the fast growth of babies who are ready for the outside world after a relatively short pregnancy might also affect risk, they say.
Whatever the reason, "if the findings are real, large birth size would be responsible for only a small proportion of the total number of cases of breast cancer in any population, as the incidence in premenopausal years is low," they say. And the breast cancer risk is balanced by the known fact that heavier babies are less likely to develop heart disease as adults, they say.
The study is interesting but necessarily flawed, says Dr. Julia A. Smith, a clinical assistant professor of medicine at New York University Medical Center.
"This is not the first time this has been postulated and looked at, but it is the first time researchers have looked at this size population," she says.
And while Sweden has the best population records of any country, the database did not include many of the important risk factors for breast cancer, such as family history and genetics, Smith says.
While it is true that the mammary gland does begin to develop before birth, it is unclear what role the mother's circulating estrogens play in that development, and the study does not address that point, she says.
More information
You can get comprehensive information about breast cancer from the National Cancer Institute. Meanwhile, the March of Dimes has tips on making your pregnancy a successful one.
