For many, the answer to “How long does pregnancy last?” is nine months, or thereabouts. (Ask a tired, and very cranky pregnant woman near the end of her pregnancy, and she may understandably answer “Way too long!”)

But if you ask a mother when she stops truly carrying her child - at least, if you ask me - the answer is a simple one: never.

The biology of motherhood and nutrition, particularly as it intersects with omega-3 and brain health, has been my primary topic of research, writing, inspiration and interest for much of my career. It’s a topic that may seem exceptionally common - after all, every person walking around today and that has ever come before us has been born and mothered by a woman.

And yet its ordinariness doesn’t diminish the marvelous chain of events that take place in a woman’s body and its highly nuanced systems which suddenly shift in order to grow and nurture another life from within. Breastmilk, for example, is a dynamic living food which is tailor-made for each individual and contains hundreds, perhaps even thousands of constituents “that are bioactive in the infant in ways we just don’t know,” according to human evolutionary biologist Dr. Katie Hinde of Harvard University (Frederick, 2014).

Calico kitten with blue eyes sitting on the floor
Chimerism can happen on a large scale as in this case when embryos from two cats – one black, one calico – merged in the womb. Microchimerism between human mother and baby is more subtle and far more common; in fact, it’s universal.

And one of the deepest, yet little-known, marvels of pregnancy and motherhood is the fact that cells from the fetus take up residence and in a sense meld with the mother’s body – a phenomenon called microchimerism. Some of those cells are cleared after the baby’s birth, but others persist for a lifetime.

And microchimerism works the other way as well – some wholly maternal cells live on in the child.

The mysteries of motherhood

While the many brain adaptations brought on by pregnancy are well-documented (deLange, 2012) thanks to sophisticated DNA sequencing, researchers have established that male DNA can reside in the brains of adult women until their death, traced back to the time when they were pregnant with boys (Chan, 2012).

Pregnancy is a physically taxing process, and there is a delicate balance to be achieved. While the progression of pregnancy is an evolutionary priority, the health of the infant must not come at the expense of the mother. Often, the demands of pregnancy seem to hit mom the hardest - for example, a pregnant woman who doesn’t have sufficient dietary intake of DHA from oily fish will not only deplete her own fat stores reserved for pregnancy since puberty, but will unknowingly become deficient as well, which is why eating plenty of salmon, sardines, and the like is so critical during pregnancy and postpartum, as Dr. William Sears recently reminded our readers.

Human babies are particularly vulnerable at birth compared to other mammals, due partially to their brain size, which then quadruples over the next three years (Dekaban, 1978). So it’s to our evolutionary advantage for moms to stick around, “both parties having an interest in the other's survival and well-being” (Boddy et. al, 2015).

Perhaps that’s why some of the key areas to which fetal cells migrate in the two-way street of cellular exchange between mother and baby seem to uniquely benefit mother’s health. Interestingly, the transfer is “asymmetrical, with more fetal cells being transferred to the mother than vice-versa” (Boddy et. al, 2015).

Fetal Cells and Maternal Healing

Some scientific papers have suggested the accumulation of a mother’s baby’s cells in her own body may be harmful, since greater amounts of fetal microchimeric cells have been found in tumors, as well as associated with autoimmune disorders and certain cancers.

However, it is not fully understood whether this is due to the fetal cells contributing to these conditions negatively by helping the disease begin or grow, or positively, by assisting the body’s defense systems. Some researchers feel the evidence favors the latter theory, and say microchimerism ought to be “associated with enhanced maternal health” (Boddy et. al, 2015).

3D rendering of DNA structure
Microchimeric cells bearing her child’s unique DNA may contribute to a mother’s health in a variety of ways.

After all, fetal cells are pluripotent, similar to certain stem cells - they can grow into a variety of tissue types, and fetal microchimeric cells have been found actively migrating to injury sites in their mother’s body.

Fetal cells have been identified in the mother’s brain cells, healed C-section scar tissue, breast cells, thyroid cells, maternal immune cells, cells lining blood vessels, neurons, smooth muscle cells, and cardiomyocytes - or heart cells (Boddy et. al, 2015). So perhaps this exchange of fetal-maternal cells is not contributing to a mother’s pathology - but rather, to her healing.

Fleeting, but Forever

In late July of 2018, I experienced a common event which had a profound impact on my life. The delight of an unanticipated pregnancy left my husband and I scrambling to accommodate a rush of new childcare needs for our third baby and all the schedule reshuffling it would require - the usual family chaos which feels so stressful in the moment and seems, in retrospect, so precious and fleeting.

Until another unexpected event occurred: an ultrasound revealed that the precious heart I carried in my womb had stopped beating. No explanation - it just stopped. And everything else stopped, too.

Suddenly, the calendar, with all its crazed scribbling of schedule shifts and planned midwife appointments was going to be empty. As empty as an uninhabited shell. As empty as my womb would be.

I carried my grief after that. It seemed that I carried it alone, until I was captivated by an image which made me feel suddenly less solitary in my small and private tragedy: The image of a whale carrying her baby who died shortly after birth - a new orca mother unwilling to let her baby descend to the murky ocean floor after carrying her for 17 months, only to hold her for a few brief hours. “Take all the time you need, sweet mama,” I whispered to Tahlequah, and to myself. She carried her baby for 17 days and 1000 miles; some people marveled and people wondered why. But some people knew why. I knew why.

And when the world celebrated, as Vital Choice founder Randy Hartnell and editor Brad Lemley joyfully and beautifully wrote when Tahlequah became a mother again last year, I wept again - this time for joy, as I held my own new baby in my arms.


here is the deepest secret nobody knows

(here is the root of the root and the bud of the bud

and the sky of the sky of a tree called life; which grows

higher than soul can hope or mind can hide)

and this is the wonder that's keeping the stars apart


i carry your heart (i carry it in my heart)


e.e. cummings


How long does a mother carry her child? We never stop. Tahlequah still carries her babies in her heart, as do I.



  • Boddy, A. M., Fortunato, A., Wilson Sayres, M., & Aktipis, A. (2015).  Fetal microchimerism and maternal health: A review and evolutionary analysis of cooperation and conflict beyond the womb. BioEssays,  37,  1106– 1118.
  • Chan, W. F., Gurnot, C., Montine, T. J., Sonnen, J. A., Guthrie, K. A., & Nelson, J. L. (2012). Male microchimerism in the human female brain. PloS one, 7(9), e45592.
  • Dekaban A. S. (1978). Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights. Annals of neurology, 4(4), 345–356.
  • de Lange, A. G., Barth, C., Kaufmann, T., Anatürk, M., Suri, S., Ebmeier, K. P., & Westlye, L. T. (2020). The maternal brain: Region-specific patterns of brain aging are traceable decades after childbirth. Human brain mapping, 41(16), 4718–4729.
  • Frederick R. (2014). Mother's milk mysteries. Proceedings of the National Academy of Sciences of the United States of America, 111(20), 7165.
  • Mahmood U, O'Donoghue K. 2014. Microchimeric fetal cells play a role in maternal wound healing after pregnancy. Chimerism 5:  40– 52