Rewarding though pregnancy may be, any mom can attest that carrying a baby into the world can take a toll on the body.
And researchers just keep adding to the list of ways that nine months of companionship can leave a lasting health impact on mother and child.
While it's a common complaint from new moms that babies scramble their brains, a new study from the Fred Hutchinson Cancer Center in Seattle shows that being pregnant with a boy typically leaves women with a dollop of male DNA in their heads.
Scientists have long known that genetic material and cells are exchanged between fetus and mother during pregnancy, but the study is the first to show that fetal cells can cross the human blood-brain barrier and thrive.
The study, published in the Journal PLOS One, reviewed brain autopsy specimens from 59 women who had died between the ages of 32 and 101. Male cells were detected in 63 percent of the subjects, in multiple brain regions. The oldest female in whom male fetal DNA was detected in the brain was 94.
Among the subjects, 33 had Alzheimer's disease and 26 had no neurological disease. The brains of the women with Alzheimer's had a slightly lower prevalence of male DNA, but the researchers cautioned against any linkage, since the numbers were so small and the pregnancy history of the women was largely unknown.
Other studies at Hutchinson and elsewhere have linked the swaps between fetus and mother to a greater or lesser risk of developing some types of cancer and autoimmune disease.
For instance, cells of fetal origin are thought to offer some protection against breast cancer, while they're associated with increased risk for colon cancer. Women who have given birth at least once have a lower risk for rheumatoid arthritis compared to women with no children.
Another study, reported in June by scientists at Tufts University in Boston, examined lung tissue from late-term pregnant mice to identify three different types of fetal cells.
They found a mixed population of cells that provide nutrients to the fetus through the placenta, stem cells that can later develop into fat, cartilage or bone, and immune-system cells.
Researchers suspect the fetal cells in the mom's bloodstream help regulate the mother's immune system to not attack the fetus, for one thing, but that stem cells are present to help repair injured maternal organs.
Studies also show that a mom's condition during pregnancy can have long-lasting effects on the baby.
One report from the University of Helsinki, Finland, published online in the journal Neurology, showed that a mother's high blood pressure during pregnancy can impact the thinking skills of a child even into old age.
The study used medical records to find blood pressure for the moms of 398 men born between 1934 and 1944. The men's thinking skills had been tested at age 20 and again when they reached an average age of 69, with the tests measuring language skills, math reasoning, and visual and spatial relationships.
They report that men whose mothers had high blood pressure while pregnant scored significantly lower at age 69 than did men who mothers did not have high blood pressure. They also scored lower at age 20 and had a greater decline in scores over the decades, particularly for math-related reasoning.
Another study, published last spring by scientists at the University of California, Davis, showed that mothers who had fevers during pregnancy were more than twice as likely to have a child with autism or developmental delay than were mothers of children who reported no fever.
The report, which appeared online in May in the Journal of Autism and Developmental Disorders, also showed that controlling fevers with Tylenol or Advil countered any negative effect on the fetus.
Other studies have pointed to various infections during pregnancy, such as the flu or measles, as possible factors in autism, but this study, based on responses to questionnaires by the mothers of more than 1,100 children in California, is the first to look at the effect of fever from any cause.
The researchers note that other research has linked inflammation from chronic illnesses to autism and that fever is the result of acute inflammation as the immune system reacts to infection or injury.