Pre-embryos

What is it about?

This short letter to Nature (Vol 321, p.376, May 1986) deplored the term "pre-embryo" that had recently been proposed for human embryos in the first 14 days after fertilization.

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Why is it important?

The word "embryo" has always been applied to the developing human from conception (fertilization) until the 8th week of intrauterine life. After 8 weeks, the word "fetus" is used. All the parts of the body are formed in the embryonic period, including the placenta. The fetal period is one of growth and maturation of the structures that were formed in the embryo. The placenta conducts the functions of lungs, kidneys and alimentary tract from implantation (7 days) until the baby is born. In the 1980s scientists involved in experimentation with human embryos invented the specious term "pre-embryo" to suggest that they were not experimenting with real human embryos that might have been able to become real human babies. Their argument was that before Day 14 the products of conception comprised cells destined to generate both the placenta and the baby. I pointed out that the placenta was an essential part of the embryo and fetus - a disposable organ needed until birth.