Motherhood is a variable experience. Some women find the nine-month incubation of a pregnancy enjoyable. But when hormones surge and nausea sets in, exhaustion makes the date of delivery seem faraway.

Dramatic physical changes occur. Blood volume doubles. The placenta nourishes the fetus and provides a natural protective barrier.

As the fetus grows, maternal weight increases and endurance wanes. Nausea from day-one often ends at three months but can continue until the birth. The mother wonders when her life will return to normal and if her clothes will ever fit again.

Miscarriages are common, bringing physical and emotional adjustment, but even following an uncomplicated delivery, life doesn’t suddenly normalize. A usually joyous time getting to know the newborn is interrupted by sleepless nights and sometimes complicated by feelings of inadequacy and depression.

A new mother must juggle schedules and if breast feeding, may pump breast milk for months so she can return to work. To communicate with her baby, she may learn and teach the infant sign-language or find herself babbling baby-talk. After an unpredictable adjustment period, a new norm is reached.

Getting back into shape, eating right, sleeping and taking care of mothering tasks prevail, but during the pregnancy, silent changes evolved in the maternal body that may impact her health for life. Fetal and maternal blood circulation are separate except for a nutritional interface. No maternal-fetal blood is exchanged but fetal deoxygenated blood passes through umbilical cord arteries to the placenta. There maternal nutrients and oxygen are exchanged through the mesh of an arterio-capillary-venous system, much like oxygen/carbon dioxide transfer occurs in adult lungs.

Despite clear separation of fetal and maternal circulation, an article published by researchers at the University of Arizona reported some fetal blood cells migrate through the placenta and are carried in the mothers’ blood. The fetal cells lodge in various maternal locations where they exist for years. Foreign cells in maternal tissue turn mothers into chimeras. The term alludes to Greek mythology and creatures built from different animal parts, in this case: fetal microchimerism. Fetal cells are detectable in 90% of healthy women after a pregnancy.

Researchers found fetal cells migrated to damaged tissue following a C-section delivery where they were actively involved in healing. In other cases, fetal cells were swept through the bloodstream into maternal areas including the lungs, where they appeared to be inactive bystanders. Some of the escaped fetal cells were pluripotent, like stem cells, able to change into different cells and impact body processes in both positive and possibly negative ways.

Health issues including autoimmune diseases might be triggered by the foreign fetal cells. In these common diseases, the body’s immune system attacks normal cells. Of note, women are more likely to develop autoimmune disorders such as rheumatoid arthritis, MS and lupus than men.

Male fetal cells are found in women who have not given birth to a male child. How could that happen? This may occur when a male embryo fails to develop properly and aborts or is absorbed by maternal processes but some of the fetal cells live on.

Another field of research has shown a reverse transfer of cells, where maternal cells migrate to the fetus. This may explain autoimmune diseases in offspring, including inflammatory bowel disease and biliary cirrhosis.

Although effects of fetal microchimerism have been studied over decades, their impact remains incompletely understood and vigorously debated within the biological research community.

Betty Kuffel, MD