What is “conception”? It’s not as clear as many people think

Marvin JS Ferrer

Out of millions of sperm, only one will fertilize an egg. The term “conception” is commonly used to describe this specific moment, and is also often treated as synonymous with the beginning of “pregnancy.” Many people think conception is a clearly defined moment, and pro-life positions are underpinned by the idea that, after conception, a human being with legal rights is created.

Premised on this idea of conception, many pro-life organizations regularly hold protests and “life chains” across Canada, with an aim to reduce women’s access to reproductive choices, and end the alleged mistreatment of human embryos and fetuses. Yet the actual process that leads to the creation of distinct humans is more gradual and complex than most people expect, weakening the apparent clarity of the idea that conception is a defined boundary.

First, a sperm cell must penetrate the egg’s tough outer coating. Once it passes through this layer, it is actually still outside of the egg. It must subsequently fuse its outer surface with the egg’s outer surface so that its genetic material can enter the egg (Figure 1 A).


Human cells generally contain a complete set of genetic material: 23 chromosomes with a copy from each the sperm and the egg for a total of 46. But when the sperm enters the egg, the egg has not yet finished maturing, and still has too many chromosomes of its own. A signal from the newly fused sperm triggers it to complete maturation.

When the egg receives this message, it divides unevenly into two, and the sperm’s genetic material remains within the bulk of the egg (Figure 1 B). The other part of the egg then dies. The sperm’s genetic material begins to disperse in the egg, but remains distinct from the egg’s genetic material until the egg finishes this division. At the completion of this step, there should be 46 chromosomes present.

It’s only following this step that maternal and paternal genetic material combine, and the single-celled embryo begins to divide rapidly (Figure 1 C).

The resulting embryo can have some strange fates. A commonly known outcome occurs when the embryo splits, thus creating two people – identical twins. There are, however, other fates that may befall the embryo in this stage. If there are multiple embryos present, such as if the embryo has a twin (identical or fraternal), it could fuse together to create a single embryo, called a chimaera. The chimaera normally has the genes of two siblings in one person, but it could also have three or four (or more!) genetic parents in the case of embryos created through in vitro fertilization, which is part of assisted reproductive technology. Chimaera can be formed by taking some early cells from embryo 1 and placing them with embryo 2’s cells. Embryo 2 will be a chimaera, and both this and embryo 1, will develop normally. After some time, the embryo’s cells begin to specialize (Figure 1 D).

pregnancyPeople who claim embryos have rights following conception also tend to believe that pregnancy begins at conception – a belief that is simply not supported by the meaning of the word “pregnancy.” Until the embryo attaches itself to the walls of the uterus, the embryo is free-floating and pregnancy has not taken place (Figure 1 E). Artificially-created embryos exist, but no one is pregnant until these embryos are introduced into a woman. Additionally, a significant proportion of embryos never implant, with no indication that an egg was ever fertilized in the first place.

The Assisted Human Reproduction Act, passed in 2004 by the Parliament of Canada, is informed by these facts. It forbids the maintenance of a human embryo for longer than 14 days outside of a uterus. After this time, the cells of the embryo are specialized enough that they can only become one individual. The Act disallows the creation of human-non-human hybrids for reproductive purposes. The Act forbids the creation of chimaeras, although they occur. However, since health care is under provincial jurisdiction, the Act uses the Criminal Code as its mechanism for regulation. Sections of the law were struck down in 2010 by the Supreme Court of Canada for encroaching on provincial jurisdiction. Health Canada has recently started to review the Act and related regulations regarding surrogacy, the donation of reproductive material, and health and safety. However, it is not thought to be reviewing rules regulating the creation, modification, or destruction of embryos.

supreme_court_of_canada_building_-_winter2012With regards to reproductive freedom, in 1988 the Supreme Court of Canada struck down laws restricting access to abortion, saying they breach women’s right to security of the person. No law or policy marks conception as a specific point where rights deserve consideration. As a medical procedure, it is publicly funded, but access is severely limited in some areas by a lack of facilities. As a result of the Supreme Court ruling, and the absence of further action from Parliament, Canada has no laws or regulations regarding abortion, and no policy in Canada currently exists other than professional guidelines by medical organizations. These guidelines are evidence-based and, most importantly, leave healthcare decisions and the promotion of well-being to the discretion of medical professionals and their patients.

When people demand policy changes recognizing that embryos deserve legal rights following conception, it is important to understand the science underpinning (and likely undermining) their claims:

  1. Conception is not pregnancy
  2. Following immediate sperm entry, the egg has too much genetic material
  3. The early embryo can become multiple distinct individuals (twins, triplets, etc.), or merge with other eggs to form one individual (chimaeras)
  4. Embryo formation is not guaranteed to initiate a pregnancy

At the very least, it is important to recognize that conception is not a line separating black-and-white states of being.

Marvin is a member of the Master of Public Policy Class of 2018 at the University of Toronto. He completed his undergraduate degree in Life Sciences and a master’s and doctoral degree in the cell biology of reproduction and fertility at Queen’s University. His policy interests include science and research policy, and health policy, and he would like to advance the use of the scientific method to improve evidence-based decision making. Marvin is now old enough to be a senator, and would appreciate it if someone mentioned this to the Prime Minister.

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