What Is The Difference Between An Embryo And A Fetus?


Bring up embryo adoption at your next dinner party and I promise you it will elicit questions. But some of those questions won’t be easy to answer. I recently ran smack into this situation in my interview with Eric Metaxas when the biology of embryo development came up. (Sidebar: Audio is now posted, and I hope you’ll give it a listen starting around the 15-minute mark. Bravo, Eric! Your smart questions fueled this blog post to help me better understand how we all began.) Meanwhile, a fetus is a larger version of that little person starting from Week 8 onto the end of the pregnancy, according to the American Pregnancy Association.

Why did the “what is an embryo” question stump me? I’m no scientist, for one thing. I married a scientist so I wouldn’t have to heed that special life calling. I can barely describe the difference between a man and a mushroom. But as a former high school jazz saxophonist, I sure know how to improvise. Or punt. In this particular case, I leaned on the expertise of our adoption agency’s embryo adoption program director — who stood just a few feet away during the interview.

It turns out an embryo is basically the earliest stage of human development. This overview from the Cleveland Clinic is especially instructive to anyone trying to get a plain English rundown of an embryo. The life of an embryo is characterized by rapid growth.

But here’s what an embryo really is, in the Cleveland Clinic’s own words: “At the moment of fertilization, your baby's genetic make-up is complete, including its sex. If a Y sperm fertilizes the egg, your baby will be a boy; if an X sperm fertilizes the egg, your baby will be a girl”. (emphasis added)

In my view, this means we in the embryo adoption community should consider two definitions to clarify the difference between an embryo and a fetus:

  • First, an embryo is a human being at its earliest stage of life. A fetus, by contrast, is a more mature human being. (Some get particularly nitpicky and break down the definition of “embryo” into an even earlier stage of “pre-embryo,” meaning babies younger than 14 days old. While I realize that term is intended to be technical and not a moral diagnosis, it strikes me as clinical at best. I reject words that explicitly or implicitly de-humanize my fellow man. Embryos have all of the biological materials necessary for life. They have unique DNA. That point cannot be argued.

  • Second, you can have an embryo without a fetus. But you cannot have a fetus without an embryo.

That last point is perhaps the most important for anyone remotely concerned about the fate of the estimated 1 million embryos in frozen storage in the U.S. It’s especially crucial at a time when movies such as “Unplanned,” which spotlight the sanctity of life, are generating more attention than anticipated. You know something is stirring across the land when The Hollywood Reporter leads with, “Controversial Anti-Abortion Pic Surprises With Strong $6M Debut”. Americans still care about the question of when life begins and whether it is morally OK to terminate a nascent life.

But very few Americans — or any of the other societies around the world — recognize that the gap that exists between embryo and fetus is a pressing moral concern. It is deeply concerning for families who have been through in vitro fertilization and are faced with the painful decision of what to do with their remaining embryos. It is deeply concerning for families facing infertility and seeking to experience pregnancy, to bring a child to term. It should concern those of us who believe all are created in God’s image.

Yet the vast majority of the people you know aren’t concerned. And I suspect a good deal of that has to do with the fact that they have accepted an embryo is different than a fetus is different than a baby. This is strikingly true among most people who identify as Christians.

A Rutgers Law School associate professor captured this irony in a 2015 guest post for The Washington Post spurred by her and her husband’s decision to donate an embryo to medical research. Her clarity on this subject ought to give all of us pause.

“If life begins at conception,” Margo Kaplan wrote, “then anti-choice groups have every reason to put the estimated 400,000 to 1 million frozen embryos in the United States at the forefront of their efforts.”

But we do not. And that might be the result of forgetting that the difference between an embryo, a fetus and a baby is this: There is no difference at all.