Thursday night, the Kansas legislature passed an anti-abortion bill declaring that life begins "at fertilization." Governor Sam Brownback, a strong abortion opponent himself, is expected to sign the bill into law to make the new restrictions enforceable by July 1.
However, anti-abortion politicians and other activists who want to define human life as beginning at fertilization may have another think coming about the legal use of this term. No one--even top scientists, doctors, or the mother herself--can determine the exact moment when a human egg is fertilized.
The Encyclopedia Britannica defines fertilization of a human egg as the merger of chromosomes from a male gamete (sperm) with those from a female gamete (ovum). It describes the process from the meeting of gametes as follows.
(1) The sperm release enzymes that help disperse the corona radiata and bind to the zona pellucida. (2) The outer sperm head layer is sloughed off, exposing enzymes that digest a path through the zona pellucida. (3) The sperm fuses with the egg cell membrane, causing the zona pellucida to become impenetrable to other sperm [thus ensuring the uniqueness of the father]. (4) The tail separates from the sperm head, and the male pronucleus enlarges and travels to the female pronucleus in the center of the cell. Chromosomes merge to form a fertilized egg.
In the late 1950s, scientists developed the ability to fertilize the eggs of mammals in vitro (within glass, outside the body). The discovery led to the first analysis of the cellular and molecular events in fertilization. The authoritative fourth edition of Molecular Biology of the Cell (2002), a medical textbook cited by the National Center for Biotechnology Information of the National Institutes of Health, describes the process of in detail.
"Of the 300,000,000 human sperm ejaculated during coitus, only about 200 reach the site of fertilization in the oviduct [fallopian tube]."
They normally get there while the egg travels from an ovary through its tube (ampulla). From there, the sperm tiebreaker begins.
While in the tube, the ovum is viable (capable of fertilization) for about 18 to 24 hours. Then it disintegrates. Sperm usually remain viable in a woman's reproductive tract for about 48 hours. This time frame can be "quite variable," says Dr. Harry H. Hatasaka, a professor of medicine at the University of Utah and author of Fertilization, Early Pregnancy and Its Disorders.
The first successful sperm wins the prize, enters the ovum (see graphic), and begins to search for the female genetic nucleus. At the outside, the whole process of haploid fusion takes from several hours to days after intercourse. "Once fertilized, the egg is called a zygote," says the molecular biology text.
"Fertilization is not complete, however, until the two haploid [half] nuclei (called pronuclei) have come together and combined their chromosomes into a single diploid [whole] nucleus. In fertilized mammalian eggs, the two pronuclei do not fuse directly as they do in many other species. They approach each other but remain distinct until after the membrane of each pronucleus has broken down in preparation for the zygote's first mitotic division."
Initial cell division takes place during the time the diploid nucleus remains in the tube. This takes about 72 hours. During this time the zygote does not grow in size. It sheds its protective shell and remains free in the uterine cavity for 60 to 72 more hours after leaving the tube.
By then, a cell mass (blastocyst) has been formed that can finally attach itself to the uterine wall. Until this happens, the cell mass has not yet reached the embryonic stage. In vitro fertility specialists do not usually harvest and freeze embryos until ten days after they implant in the uterus.
So the time of fertilization has little to do with when male and female partners perform their ancient dance.
The speed of haploid fusion is the first limitation and applies to those like the Kansas legislators who appear to be defining fertilization as the formation of a diploid nucleus. However, depending on which physician you talk with, it can take up to 16 days for a viable embryo to form, attach, and be separable from a woman's body. Natural spontaneous abortion (miscarriage) can occur at any time after fertilization without the mother's or a doctor's knowledge, although it usually happens within three months after coitus.
It's important to note here that the makers of emergency contraception only allow a 72-hour window for the use of their drug. This follows a very strict interpretation of the allowable time. Legislators do not always consult with the experts before turning mistaken (i.e., not evidence-based) science into the rule of law. The distinction between scientific theory and measurable results has been recognized since the 17th century.
Based in Chicago, Sandy Dechert has covered healthcare for Examiner.com since the webzine's official startup. Involved in contraceptive science and technology since the late 1980s, she has also followed the creation and progress of health care legislation over the past two decades. Ms. Dechert's work also includes other top health stories, such as the 2012-2013 influenza epidemic and the fungal meningitis outbreaks, and incorporates a focus on sexual and women's health.
This publication is not a substitute for professional medical advice. See a qualified health care professional if you have any questions.
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