chapter 21

Sperm that cannot readily enter the oocyte may be sucked up into a tiny syringe and microinjected into the female cell. This technique, called intracytoplasmic sperm injection (ICSI), is more effective than IVF alone and has become standard at some facilities. ICSI is very helpful for men who have low sperm counts or many abnormal sperm. It makes fatherhood possible for men who cannot ejaculate, such as those who have suffered spinal cord injuries. ICSI has been performed on thousands of men with about a 30 percent success rate.

Two to five days after sperm wash over the oocytes in the dish, or are injected into them, a blastocyst is transferred to the uterus. If the hormone human chorionic gonadotropin appears in the woman's blood a few days later, and its level rises, she is pregnant. IVF costs from on average $8,158 per cycle. Medications can add $3,000 to $5,000 to the cost. ICSI adds another $1,544 on average. Children born following IVF have a slight increase in the rate of birth defects (about 8 percent) compared to children conceived naturally (about 3 percent). This difference may be due to the medical problems that caused the parents to seek IVF, the tendency of IVF to interfere with the parting of chromosome pairs during meiosis, closer scrutiny of IVF pregnancies, and/or effects on imprinting from the time spent in culture.

A Donated Uterus—Surrogate Motherhood

1) If a man produces healthy sperm but his partner's uterus cannot maintain a pregnancy, a surrogate mother may help by being inseminated with the man's sperm. When the child is born, the surrogate mother gives the baby to the couple. In this variation of the technology, the surrogate is both the genetic and the gestational mother. 2)A problem with surrogate motherhood is that a woman may not be able to predict her responses to pregnancy and childbirth in a lawyer's office months before she must hand over the baby. When a surrogate mother changes her mind, the results are wrenching for all. 3)Another type of surrogate mother lends only her uterus, receiving a fertilized ovum conceived from a man and a woman who has healthy ovaries but lacks a functional uterus. This variation is an "embryo transfer to a host uterus," and the pregnant woman is a "gestational-only surrogate mother." She turns the child over to the biological parents.

Problems can arise in IUI if a donor learns that he has an inherited disease. For example, a man developed cerebellar ataxia, a movement disorder, years after he donated sperm. Eighteen children conceived using his sperm face a 1 in 2 risk of having inherited the mutant gene.

A male's role in reproductive technologies is simpler than a woman's. A man can be a genetic parent, contributing half of his genetic self in his sperm, but a woman can be both a genetic parent (donating an oocyte) and a gestational parent (donating the uterus).

IVF may fail because of the artificial environment for fertilization. A procedure called GIFT, which stands for gamete intrafallopian transfer, improves the setting. (Uterine tubes are also called fallopian tubes.) Fertilization is assisted in GIFT, but it occurs in the woman's body rather than in glassware. In GIFT, several of a woman's largest oocytes are removed. The man submits a sperm sample, and the most active cells are separated from it. The collected oocytes and sperm are deposited together in the woman's uterine tube, at a site past any obstruction that might otherwise block fertilization. GIFT is about 22 percent successful.

A variation of GIFT is ZIFT, which stands for zygote intrafallopian transfer. In this procedure, an IVF ovum is introduced into the woman's uterine tube. Allowing the fertilized ovum to make its own way to the uterus increases the chance that it will implant. ZIFT is also 22 percent successful. GIFT and ZIFT are done less frequently than IVF. These procedures may not work for women who have scarred uterine tubes. The average cost of GIFT or ZIFT is $15,000 to $20,000.

In in vitro fertilization (IVF), which means "fertilization in glass," sperm and oocyte join in a laboratory dish. Soon after, the embryo that forms is placed in a uterus. If all goes well, it implants into the uterine lining and continues development until a baby is born.

A woman might undergo IVF if her ovaries and uterus work but her uterine tubes are blocked. Using a laparoscope, which is a lit surgical instrument inserted into the body through a small incision, a physician removes several of the largest oocytes from an ovary and transfers them to a culture dish. If left in the body, only one oocyte would exit the ovary, but in culture, many oocytes can mature sufficiently to be fertilized in vitro. Chemicals, sperm, and other cell types similar to those in the female reproductive tract are added to the culture. An acidic solution may be applied to the zona pellucida, which is the layer around the egg, to thin it to ease the sperm's penetration.

A number of medical tests can identify causes of infertility. The man is checked first, because it is easier, less costly, and less painful to obtain sperm than oocytes.Sperm are checked for number (sperm count), motility, and morphology (shape).

An ejaculate containing up to 40 percent unusual forms is still considered normal, but many more than this can impair fertility. A urologist performs sperm tests. A genetic counselor can evaluate Y chromosome deletions associated with lack of sperm.

In the past, several embryos were implanted to increase the success rate of IVF, but this led to many multiple births, which are riskier than single births. In some cases, physicians had to remove embryos to make room for others to survive. To avoid the multiples problem, and because IVF has become more successful as techniques have improved, guidelines now suggest transferring only one embryo.

Embryos resulting from IVF that are not soon implanted in the woman can be frozen in liquid nitrogen ("cryopreserved" or "vitrified") for later use. Cryoprotectant chemicals are used to prevent salts from building up or ice crystals from damaging delicate cell parts. Freezing takes a few hours; thawing about a half hour. The longest an embryo has been frozen, stored, and then successfully revived is 13 years; the "oldest" pregnancy using a frozen embryo occurred 9 years after the freezing.

Uterine tubes can also be blocked due to a birth defect or, more likely, from an infection such as pelvic inflammatory disease. A woman may not know she has blocked uterine tubes until she has difficulty conceiving and medical tests uncover the problem. Surgery can open blocked uterine tubes.

Excess tissue growing in the uterine lining may make it inhospitable to an embryo. This tissue can include benign tumors called fibroids or areas of thickened lining from a condition called endometriosis. The tissue can grow outside of the uterus too, in the abdominal cavity. In response to the hormonal cues to menstruate, the excess lining bleeds, causing cramps. Endometriosis can hamper conception, but curiously, if a woman with endometriosis conceives, the cramps and bleeding usually disappear after the birth.

A technique called sequential polar body analysis may substitute for PGD and provides genetic information even earlier in development. The approach is based on the fact that meiosis completes in the female only as a secondary oocyte is fertilized.

If a woman is heterozygous for a mutation, then an oocyte would inherit the mutation and its associated polar bodies would inherit the wild type allele, or vice versa. This is in accordance with Mendel's first law, gene segregation. The timetable of female meiosis is important, too. The first polar body forms as the developing oocyte leaves the ovary. That polar body is not accessible, and it would not show the effects of crossing over. A second polar body, however, which forms at fertilization, can be tested

The uterine tubes are a common site of female infertility because fertilization usually occurs in open tubes. Blockage can prevent sperm from reaching the oocyte, or entrap a fertilized ovum, keeping it from descending into the uterus.

If an embryo begins developing in a blocked tube and is not removed and continues to enlarge, the tube can burst and the woman can die. Such a "tubal pregnancy" is called an ectopic pregnancy.

Embryo adoption is a variation on oocyte donation. A woman with malfunctioning ovaries but a healthy uterus carries an embryo that results when her partner's sperm is used in intrauterine insemination of a woman who produces healthy oocytes.

If the woman conceives, the embryo is gently flushed out of her uterus a week later and inserted through the cervix and into the uterus of the woman with malfunction- ing ovaries. The child is genetically that of the man and the woman who carries it for the first week, but is born from the woman who cannot produce healthy oocytes. "Embryo adoption" also describes use of IVF "leftovers."

To avoid the difficulty of freezing oocytes, strips of ovarian tissue can be frozen, stored, thawed, and reimplanted at various sites, such as under the skin of the forearm or abdomen or in the pelvic cavity near the ovaries. The tissue ovulates and the oocytes are collected and fertilized in vitro. The first child resulting from fertilization of an oocyte from reimplanted ovarian tissue was born in 2004. The mother, age 25, had been diagnosed with advanced Hodgkin's lymphoma. The harsh chemotherapy and radiation cured her cancer, but destroyed her ovaries. Beforehand, five strips of tissue from her left ovary were frozen.

Later, several pieces of ovarian tissue were thawed and implanted in a pocket that surgeons crafted on one of her shriveled ovaries, near the entrance to a uterine tube. Menstrual cycles resumed, and shortly thereafter, the woman became pregnant with her daughter, who is healthy. Freezing ovarian tissue may become routine for cancer patients of child- bearing age. Women who have no oocytes or wish to avoid passing on a mutation can obtain oocytes from donors, who are typically younger women. Some women become oocyte donors when they undergo IVF and have "extra." The potential father's sperm and donor's oocytes are placed in the recipient's uterus or uterine tube, or fertilization occurs in the lab- oratory and a blastocyst is transferred to the woman's uterus.

Infertility in the male is easier to detect but sometimes harder to treat than female infertility. Four in 100 men in the general population are infertile, and half of them do not make any sperm, a condition called azoospermia. Some men have difficulty fathering a child because they produce fewer than the average 20 to 200 million sperm cells per milliliter of ejaculate. This condition, called oligospermia, has several causes. If a low sperm count is due to a hormonal imbalance, administering the appropriate hormones may boost sperm output. Sometimes a man's immune system produces IgA antibodies that cover the sperm and prevent them from binding to oocytes. Male infertility can also be due to a varicose vein in the scrotum. This enlarged vein emits heat near developing sperm, which prevents them from maturing. Surgery can remove a scrotal varicose vein.

Most cases of male infertility are genetic. About a third of infertile men have small deletions of the Y chromosome that remove the only copies of key genes whose products control spermatogenesis. Other genetic causes of male infertility include mutations in genes that encode androgen receptors or protein fertility hormones, or that regulate sperm development or motility.

Oocytes can be stored, as sperm are, but the procedure may create problems. Because an oocyte is the largest type of cell, it contains a large volume of water. Freezing can form ice crystals that damage cell parts. Candidates for preserving oocytes include women who wish to have children later in life and women who will contact toxins or teratogens in the workplace or in chemotherapy.

Oocytes are frozen in liquid nitrogen at -30°C to -40°C, when they are at metaphase of the second meiotic division. At this time, the chromosomes are aligned along the spindle, which is sensitive to temperature extremes. If the spindle comes apart as the cell freezes, the oocyte may lose a chromo- some, which would devastate development. Another problem with freezing oocytes is retention of a polar body, leading to a diploid oocyte.

Like most ARTs, use of PGD has expanded as it has become more accurate and more familiar. Today it has taken on a quality-control role in addition to being a tool to detect and prevent rare diseases. PGD is increasingly being used to screen early embryos derived from IVF for normal chromosome number before implanting them into women. This selection process should increase the chances of successful live births, but in the first large trial, PGD actually lowered the birth rate—perhaps intervention harmsembryos.

PGD can introduce a bioethical "slippery slope" when it is used other than to ensure that a child is free of a certain disease. Some people may regard gender selection using PGD as a misuse of the technology.

prenatal diagnostic tests such as amniocentesis and chorionic villus sampling can be used in pregnancies achieved with assisted reproductive technologies. A test called preimplantation genetic diagnosis (PGD) detects genetic and chromosomal abnormalities before pregnancy starts. The couple selects a very early "preimplantation" embryo that tests show has not inherited a specific detectable genetic condition. "Preimplantation" refers to the fact that the embryo is tested at a stage prior to when it would implant in the uterus.

PGD is possible because one cell, or blastomere, can be removed for testing from an 8-celled embryo, and the remaining seven cells can complete development normally in a uterus. Before the embryo is implanted into the woman the single cell is karyotyped, or its DNA amplified and probed for genes that the parents carry. It may soon be more economical to sequence the exome or genome in place of these more specific tests. Embryos that pass these tests are selected to complete development or are stored. At first, researchers implanted the remaining seven cells, but letting the selected embryo continue developing in the dish until day 5, when it is 80 to 120 cells, is more successful. Obtaining the cell to be tested is called "blastomere biopsy" . Accuracy in detecting a mutation or abnormal chromosome is about 97%. Errors generally happen when a somatic mutation affects the sampled blastomere but not the rest of the embryo. Amplification of selected blastomere DNA may cause such somatic mutation

In another technology, cytoplasmic donation, older women have their oocytes injected with cytoplasm from the oocytes of younger women to "rejuvenate" the cells. Although resulting children conceived through IVF appear to be healthy, they are being monitored for a potential problem— heteroplasmy, or two sources of mitochondria in one cell.

Researchers do not yet know the health consequences, if any, of having mitochondria from the donor cytoplasm plus mitochondria from the recipient's oocyte. These conceptions also have an elevated incidence of XO syndrome, which often causes spontaneous abortion.

Fertility drugs can stimulate ovulation, but they can also cause women to "superovulate," producing and releasing more than one oocyte each month. A commonly used drug, clomiphene, raises the chance of having twins from 1 to 2 percent to 4 to 6 percent. If a woman's ovaries are completely inactive or absent (due to a birth defect or surgery), she can become pregnant only if she uses a donor oocyte.

Some cases of female infertility are due to "reduced ovarian reserve"—too few oocytes. This is typically discovered when the ovaries do not respond to fertility drugs. Signs of reduced ovarian reserve are an ovary with too few follicles (observed on an ultrasound scan) or elevated levels of follicle-stimulating hormone on the third day of the menstrual cycle.

For many men with low sperm counts, if they have at least 60 million sperm cells per ejaculate, fertilization is likely eventually. To speed conception, a man with a low sperm count can donate several semen samples over a period of weeks at a fertility clinic. The samples are kept in cold storage, then pooled.

Some of the seminal fluid is withdrawn to leave a sperm cell concentrate, which is then placed in the woman's body. It isn't very romantic, but it is highly effective at achieving pregnancy. Men who actually want a very low sperm count—those who have just had a vasectomy for birth control—can use an at-home test kit to monitor their sperm counts.

Infertility is the inability to conceive a child after a year of frequent intercourse without the use of contraceptives.

Some specialists use the term subfertility to distinguish those individuals and couples who can conceive unaided, but for whom this may take longer than average.

Sperm quality is more important than quantity. Sperm cells that are unable to move or are shaped abnormally cannot reach an oocyte. Inability to move may be due to a hormone imbalance, and abnormal shapes may reflect impaired apoptosis (programmed cell death) that normally removes such sperm.

The genetic package of an immobile or abnormally shaped sperm cell can be injected into an oocyte and sometimes this leads to fertilization. However, even sperm that look and move normally may be unable to fertilize an oocyte.

Abnormalities in any part of the female reproductive system can cause infertility. Many women with subfertility or infertility have irregular menstrual cycles, making it difficult to pinpoint when conception is most likely. In an average menstrual cycle of 28 days, ovulation usually occurs around the 14th day after menstruation begins. At this time a woman is most likely to conceive.

The hormonal imbalance that usually underlies irregular ovulation has various causes. These include a tumor in the ovary or in the pituitary gland in the brain that controls the reproductive system, an underactive thyroid gland, or use of steroid-based drugs such as cortisone. If a nonpregnant woman produces too much prolactin, the hormone that pro- motes milk production and suppresses ovulation in new mothers, she will not ovulate.

The oldest assisted reproductive technology is intrauterine insemination (IUI), in which a doctor places donated sperm into a woman's cervix or uterus. The success rate is 5 to 15% per attempt. The sperm are first washed free of seminal fluid, which can inflame female tissues. A woman might seek IUI if her partner is infertile or has a mutation that the couple wishes to avoid passing to their child. Women also undergo IUI to be a single parent without having sex, or a lesbian couple may use it to have a child

Today, donated sperm are frozen and stored in sperm banks, which provide the cells to obstetricians who perform the procedure. IUI costs on average $865 per cycle A couple who chooses IUI can select sperm from a catalog that lists the personal characteristics of donors, such as blood type, hair and eye color, skin color, build, educational level, and interests. Some traits have nothing to do with genet- ics. If a couple desires a child of one sex—such as a daughter to avoid passing on an X-linked disorder—sperm can be separated into fractions enriched for X-bearing or Y-bearing sperm.

secretions in the vagina and cervix may be hostile to sperm. Cervical mucus that is thick or sticky due to infection can entrap sperm, keeping them from moving far enough to encounter an oocyte. Vaginal secretions may be so acidic or alkaline that they weaken or kill sperm. Douching daily with an acidic solution such as acetic acid (vinegar) or an alkaline solution such as bicarbonate, can alter the pH of the vagina so that in some cases it is more receptive to sperm cells.

Too little mucus can prevent conception too; this is treated with low daily doses of oral estrogen. Sometimes mucus in a woman's body has antibodies that attack sperm. Infertility may also result if the oocyte does not release sperm-attracting biochemicals.