woman carrying baby at beach during sunset
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You carry your child in your womb for 9 months, in your arms for 3 years, and in your heart forever.”

The first two parts of this sound like pretty accurate descriptions of pregnancy and the early years of motherhood. The last sounds like a figurative description of the immense and overwhelming love that you feel for your child. The desire to hold them close and keep them safe. The way motherhood makes our hearts feel full and like they could break into a million pieces at the same time. We actually do, though. We literally carry our children(‘s fetal cells) in our hearts forever. And, it’s beautiful.

Babies develop from fetal cells during pregnancy. Fetal cells (like stem cells) can grow into many kinds of tissue, which is how different parts of the baby develop in the womb. During pregnancy, some fetal cells cross the placenta and enter the mother’s body. Some of the fetal cells circulate with the mother’s blood unchanged. If you’ve been pregnant in the last few years, you may have been offered a genetic screening test in the first trimester. The screening test is a simple maternal blood draw that takes advantage of this fact. (This was not offered to me when I was pregnant with my 6 year old, but was for the pregnancy of my 3 year old.) The baby’s DNA is isolated from the mother’s blood and screened for genetic information. Other fetal cells that have crossed the placenta will start to grow with the mother’s cells into different types of tissue in her body just like they are growing into different tissue in the womb. After the pregnancy, the mother’s immune system removes fetal cells that are circulating in the blood, but it ignores those that have already started to grow into maternal tissue. These cells – her baby’s fetal cells – can remain in the mother’s body for the rest of her life.

On a clinical and scientific level this is all fascinating. It’s a marvel to be able to do a minimally invasive genetic screen so early in a pregnancy. It’s incredible that fetal cells can grow into all sorts of tissues. Our immune system is impressive at detecting unfamiliar DNA in the blood. It’s interesting that fetal cells growing in tissue aren’t detected by the immune system. The biology of it all is really quite amazing. It’s also a situation where the scientific understanding makes me step back at the beauty of how things actually are. As a species, we’ve historically tried to create explanations for things that we don’t yet understand. This has led to some pretty magical ideas of how things work, but I often find that the truth that we uncover with science is more awe-inspiring than what we could have ever imagined.

We literally carry our children in our hearts forever.

This makes me feel profoundly connected to my children and also to my mother, who is carrying my fetal cells in her heart. I snuggle my children in my arms and am comforted that they are also nestled in my heart. No matter where they go, I will always carry my children with me. And, no matter where I go I am always carried by my own mother. The lineage of love is reinforced by the lineage of cells.

As pregnancy and infant loss is likely on the hearts of many today, I also want to send love to all the mothers that never got to or no longer get to hold their babies in their arms. Fetal cells cross the placenta very early in pregnancy. I hope that you may find some comfort in the fact that your babies are cradled safely in your hearts as well.

Happy Mother’s Day, Friends!