Babies whose mothers experienced high anxiety while pregnant had stifled immune responses to vaccinations at 6 months old, according to a new study. However, this lowered immune response was only found when infants hadn’t received the full course of the vaccine.
“It’s not as if the experience of stress is going to be more powerful than an immunization,” said study researcher Tom O’Connor, Ph.D., a professor of psychiatry at the University of Rochester Medical Center. “At non-optimal levels of protection from immunization, we do see the effect of prenatal anxiety.”
Therefore, stressed moms don’t need to worry that their vaccinated babies are more prone to infectious disease. What the study does show, however, is that the human immune system is similar to other animals in its response to prenatal stress.
“Both in rat and in monkey studies, stress in pregnancy is associated in the offspring with reduced immune competence,” O’Connor said.
For the study, the researchers recruited 20- to 34-year-old pregnant women to fill out questionnaires regarding their levels of anxiety at eight to 12 weeks of pregnancy. The researchers filtered those women down to the most and least anxious, resulting in a total of 210 women.
These women participated in anxiety interviews at 20 and 32 weeks gestation and also provided saliva samples so researchers could measure their levels of the stress hormone cortisol. After giving birth, the moms gave permission for their babies to be tested for their immune response to the Hepatitis B vaccine.
This vaccine is typically given in three doses — the first is within days of birth, the second is at 2 months of age and the third at 6 months of age.
At two months, no link was found between mom’s pregnancy stress and baby’s immune response. This is likely because the immune system is immature and not particularly responsive at that young of an age, O’Connor said.
At 6 months, however, the babies began to show some differences. Before the third dose of the Hepatitis B vaccine, those with stressed moms showed a weaker immune response to the vaccine than those with relaxed moms.
The immune response was measured by drawing blood and finding the babies’ level of antibodies, proteins used by the immune system to locate specific invaders.
In babies who had received the full three-dose course of the vaccine, however, the effect of mom’s stress during pregnancy disappeared.
In a second experiment, the researchers exposed the babies’ immune cells to molecules designed to evoke a response. They found that in babies of stressed moms, some responses were actually overly aggressive. Therefore, mom’s anxiety during pregnancy doesn’t simply weaken the immune system, it changes the immune system’s components.
These finding may help explain previous studies that have linked maternal stress to children’s asthma and autoimmune disorders, which occur when the body attacks itself, O’Connor said.
The results showed a “dose-response” pattern, O’Connor said, so the more anxiety a pregnant mom experienced, the greater the effects on the child’s immune system.
“The key issue that various folks are struggling with is to find out if interventions in pregnancy can reduce the effects,” O’Connor said. “We just don’t know the answer to that yet.”