Mothers, from their genetic makeup to the food they eat, can have a profound effect on the development of the child growing inside them. Consider it part and parcel of sharing the same body for nine months.
But when it comes to a baby's health, it is not only these tangible variables that matter. Now a collection of new research further explores the roots of asthma and allergies, tracing them back to the womb.
"It's almost natural to continue this way," said Dr. Andy Liu, director of Pediatric Allergy and Immunology at National Jewish Medical and Research Center in Denver. "It's where causation starts."
Four studies, presented this weekend at the meeting of the American Thoracic Society in Toronto, explore how some of the less-obvious aspects of a mother's life during pregnancy -- such as her living environment or whether she delivers by Caesarean section -- can affect the baby's developing immune system and the risk of having asthma and allergies.
Among children under 18 years old in the United States, 9 million have been diagnosed with asthma and allergies, according to the American Academy of Allergy, Asthma, and Immunology.
"Increasingly, research suggests that exposures that you might encounter during early development in utero may predict a number of health outcomes," said Dr. Rosalind Wright, assistant professor of medicine at Harvard Medical School.
Wright and colleague Junenette Peters conducted a first-of-its-kind study that examined the effects of a mother's stress levels on the immune system of her babies before they were born.
Wright and Peters used a detailed questionnaire to determine how many stressors, including financial problems, relationship problems and health worries mothers-to-be experienced. They also measured the amount of dust mites, a common allergen, in the mothers' homes. Once the babies were born, the researchers measured blood levels of a particular antibody that acts as a marker for the child's allergic immune response, the IgE antibody.
Wright and Peters found that higher IgE levels correlated with higher stress levels during pregnancy, and the child was more likely to develop asthma and allergies. This effect was even more pronounced when the mother was exposed to low levels of dust mite allergens in her home during pregnancy, suggesting that the stress was the primary factor affecting the child's immune system.
Biologically, a mother has an enormous effect on her child's immune system. The baby is exposed to allergens the mother encounters through the placenta. During the third trimester, the mother begins to transfer her antibodies to the baby as well, building up the baby's immune system so that it has some measure of protection after it is born.
"The genetics are really an important part of asthma," said Dr. Devang Doshi, director of Pediatric Allergy, Immunology, and Pulmonology at William Beaumont Hospital in Royal Oak, Mich., adding that identifying it in children is key. "Research is really shifting in that direction."
But some believe there are other ways to protect the baby and boost its developing immune system even before it is born.