Our selves, other cells

Is it any solace to sentimental mothers that their babies will always be part of them?

I’m not talking about emotional bonds, which we can only hope will endure. I mean that for any woman that has ever been pregnant, some of her baby’s cells may circulate in her bloodstream for as long as she lives. Those cells often take residence in her lungs, spinal cord, skin, thyroid gland, liver, intestine, cervix, gallbladder, spleen, lymph nodes, and blood vessels. And, yes, the baby’s cells can also live a lifetime in her heart and mind.

Here’s what happens.

During pregnancy, cells sneak across the placenta in both directions. The fetus’s cells enter his mother, and the mother’s cells enter the fetus. A baby’s cells are detectable in his mother’s bloodstream as early as four weeks after conception, and a mother’s cells are detectable in her fetus by week 13. In the first trimester, one out of every fifty thousand cells in her body are from her baby-to-be (this is how some noninvasive prenatal tests check for genetic disorders). In the second and third trimesters, the count is up to one out of every thousand maternal cells. At the end of the pregnancy, up to 6 percent of the DNA in a pregnant woman’s blood plasma comes from the fetus. After birth, the mother’s fetal cell count plummets, but some stick around for the long haul. Those lingerers create their own lineages. Imagine colonies in the motherland.