Chapter 21Reproductive Technologies

CHAPTER OVERVIEW

Assisted reproductive technologies provide several ways for people to have children who might not otherwise be able to do so. This chapter investigates the biological basis of male and female infertility, tests used to diagnosis infertility, and the technologies used to produce babies in the laboratory. Combining the technique of IVF or ZIFT with preimplantation genetic diagnosis (PGD) allows genetic screening of an early embryo prior to the transfer to the uterus. Polar body biopsy enables eggs to be screened before fertilization. The use of reproductive technologies presents new ethical considerations and moral dilemmas. For example, one issue that has arisen is what should be done with unwanted frozen embryos from fertility clinics? Another concern is that new technologies such as PGD will potentially lead to eugenics.

Chapter Outline

21.1 Savior Siblings and More

  1. Assisted reproductive technologies (ARTs) provide several ways for people to have children who might not otherwise be able to do so.
  2. Countries vary in the extent of their regulation of ARTs.

21.2 Infertility and Subfertility

1.Infertility is the inability to conceive a child after one year of trying.

2.The cause of infertility can be determined about 90% of the time. The male contributes about 30% of the time, the female 60%, or both partners may be involved.

3.Subfertility is used to describe couples that can conceive unaided, but require a longer time to succeed.

Male Infertility

  1. Male infertility may be due to low sperm count, sperm that are immobile or abnormal in structure.
  2. Around one third of the cases of male infertility involve deletions of genes involved in spermatogenesis located on the Y chromosome.
  3. Infertility affects about 4% of men.

Female Infertility

  1. Female infertility can be due to an irregular menstrual cycle or blocked fallopian tubes.
  2. Fibroid tumors, endometriosis, or a misshapen uterus may prevent implantation of a fertilized ovum, and secretions in the vagina and cervix may inactivate or immobilize sperm.
  3. Oocytes may fail to release a sperm-attracting biochemical.
  4. Early pregnancy losses due to abnormal chromosome number may be mistaken for infertility; this is more common among older women.

Infertility Tests

  1. Medical tests to identify the cause of infertility are conducted on the male first.
  2. Sperm are checked for number, motility, and morphology.
  3. Genetic analysis of the Y chromosome may reveal deletions.
  4. If the male is fertile, a gynecologist will examine the structures of the woman’s reproductive system and conduct tests to assess female infertility.

21.3 Assisted Reproductive Technologies

Donated Sperm—Intrauterine Insemination

  1. In artificial insemination, donor sperm are placed into a woman's reproductive tract.
  2. X-bearing and Y-bearing sperm can be enriched to enhance sex selection.

A Donated Uterus—Surrogate Motherhood

  1. A genetic and gestational surrogate mother is artificially inseminated with sperm and provides her uterus for nine months.
  2. A gestational surrogate carries a fetus conceived in vitro with gametes from the genetic parents.

In Vitro Fertilization

  1. In IVF, a sperm and an oocyte meet in a laboratory dish and an early embryo is then transferred to the uterus.
  2. Intracytoplasmic sperm injection (ICSI) can enable immobile sperm to fertilize an oocyte.
  3. Preimplantation embryos can be frozen for later use.

Gamete and Zygote Intrafallopian Transfer

  1. In GIFT, sperm and oocytes are placed together in a fallopian tube past a blockage.
  2. In ZIFT, a preimplantation embryo conceived in vitro is placed in a fallopian tube.

Oocyte Banking and Donation

  1. The oocytes used for IVF can be donated.
  2. Embryo adoption involves an oocyte donor who is artificially inseminated.
  3. The donor then has a preimplantation embryo washed out of her uterus and transferred to the gestational mother.
  4. Cytoplasmic donation is a technology that is used to rejuvenate the oocytes of older women with the injected cytoplasm of oocytes from a younger woman.
Preimplantation Genetic Diagnosis

1.Cells can be removed from early embryos and screened for genetic and chromosomal abnormalities in a procedure termed preimplantation genetic diagnosis (PGD).

21.4 Extra Embryos

1.Extra oocytes, fertilized ova and embryos from IVF procedures are stored indefinitely, donated, discarded or used in research.

2.Polar body biopsy can be used to genotype the oocyte.

3.Oocytes free of genetic disorders can be fertilized in vitro. PGD can confirm the "health" of the embryo.

IDEAS FOR CLASSROOM DISCUSSION

Have students research bioethical issues of designer families. A technique called MicroSort is being used in clinical trials as a way to separate Y and X bearing sperm. The MicroSort technique makes use of the fact that Y chromosome bearing sperm contain 2.8% less DNA than X bearing sperm. Sperm are mixed with a fluorescent dye that reversibly binds DNA, and X bearing sperm are separated from Y bearing sperm by laser activated flow cytometry. This technique is being used to select for X chromosome bearing sperm for patients with X-linked diseases (to prevent the birth of a male “affected” child) and for family balancing purposes. Ask students to break into small groups, prepare answers to the following questions, and then share their conclusions with the class.

1.Assuming this technique is safe, should it be made available to all couples?

2.Should sperm banks offer to separate donor sperm so customers can choose the gender of a child as a menu option?

INTERNET RESOURCES AND ACTIVITIES

  1. “Bioethics Discussion Pages.” 2004. Moderated by Maurice Bernstein, M.D. These pages contain numerous bioethical questions and comments from readers. Many questions are relevant to reproductive technology. For example: “Should society have a role in regulating multiple fetal births? What are the ethical implications of becoming a 63-year-old mother? Is it ethical to commercialize and sell eggs and sperm for reproduction?”

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  1. “Human Reproduction Problem Set.” 2004. The Biology Project, University of Arizona. This problem set is designed to help students understand the human reproductive system. It covers such topics as the anatomy of the male and female reproductive systems, the hormones that influence these systems, fertilization, sterilization, and transmission of HIV.
  1. Stuben, J.1996. “The Smokescreen of Preimplantation Diagnosis.” Biomedical Ethics, 1(2). What are the ethical and moral considerations of using preimplantation genetic diagnosis (PDG). Paper examines attitudes toward PGD and PND and how this ethical and moral climate may affect the future use of reproductive technologies. <

ADDITIONAL QUESTIONS

  1. A woman donates oocytes that undergo IVF using sperm from a donor. Three 4-celled embryos are implanted into her uterus. One ceases developing. The child born from this pregnancy has testes and a penis, but internally has an ovary and a fallopian tube. Cells sampled from different parts of the body are either XX or XY. How did this child develop two types of cells, differing in sex chromosome constitution?
  1. In the United Kingdom, the number of embryos that can be implanted into a woman following IVF has been limited to three. Why would this be done?
  1. What are the ethical arguments for and against using sperm from a deceased man to fertilize ova in vitro?
  1. Of all births resulting from assisted reproductive technologies, 37% are multiple. Among natural pregnancies, only 2% are twins, and less than 1% are higher multiples. Cite sources of multiple gestations in assisted reproductive technologies.
  1. What would be the biological advantage of a woman freezing oocytes when in her twenties, for use when she is in her forties?
  1. Identical twin boys are born 7 years apart. How is this possible?
  1. Researchers delete the genes that cause disease from Salmonella bacteria, and add a gene that encodes a protein that is normally on the zona pellucida of cats. They put these bacteria into bait, where they function as birth control for wild cats that eat the bait. Explain how this works.

ANSWERS TO ADDITIONAL QUESTIONS

  1. Two of the embryos fused. One was male, one female.
  1. The number of implanted embryos is limited to prevent too many from developing, which would threaten the survival of all.
  1. Using sperm from a deceased man would be considered unethical if the man did not know he would be fathering a child.
  1. Superovulation drugs; implanting several embryos in ZIFT or IVF; several conceptions occurring with GIFT.
  1. Oocytes taken from younger women would be less likely to undergo nondisjunction, but a woman might not want to have children until her forties.
  1. The younger boy was a frozen embryo for 7 years.
  1. A cat's immune system attacks the genetically engineered Salmonella. It then attacks the animal's oocytes, recognizing the zona pellucida antigen as bacterial.