This blood disorder occurs if the woman’s blood is Rh negative and she is carrying a baby whose blood is Rh positive and she has previously been sensitized to Rh-positive blood. The woman can be sensitized through miscarriage, elective abortion, amniocen­tesis, a previous full-term pregnancy, or a blood transfusion of Rh-positive blood. In each situation except the last, Rh-positive blood has passed from the fetus to the Rh-negative woman. During subse­quent pregnancies, the woman produces antibodies directed against the fetus’s Rh-positive blood cells because her immune system recognizes the Rh-positive blood cells as “foreign.” The maternal antibodies, resulting in the development of profound anemia, destroy the fetal blood cells.

If the fetus is found to be severely anemic before he or she is mature enough to be delivered safely (about 30 weeks’ gestation), one or more blood transfusions are given via a fetoscope (fiberoptic viewing tube). The blood is transfused into one of the blood vessels in the umbilical cord. Alternatively, blood may be injected directly into the heart of the fetus via a needle passed through the mother’s abdominal wall and into the uterus. This obstetrical technique is called intracardiac transfusion and relies on accurate visualization of the fetus with ultrasound scanning. Although these measures carry some risk of inducing a miscarriage, the risk is usually justified because the ultimate outlook is excellent if the fetus can be kept alive long enough for birth to be feasible.

Sometimes, ultrasound tests show the presence of a defect in the fetus’s urinary system, causing obstruc­tion and pressure on the kidneys. In these circum­stances, a fetoscope may be used to perform a simple operation to relieve the pressure and thus limit any damage to the kidneys.

Ultrasound scanning

Ultrasound scanning is an obstetrical equipment or instrument that is part of the care given to many pregnant women. The scanning technique, which uses the echoes of high-pitched sound waves to con­struct an image of the fetus, is considered harmless and causes no discomfort. The ultrasound image enables the obstetrician to identify multiple pregnan­cies, to measure the size of the fetus (enabling its age to be assessed), and to detect certain physical and developmental defects (such as anencephaly, spina bifida, or some congenital heart abnormalities) early in the pregnancy.

Fetoscopy

Ultrasound provides relatively clear images of a developing fetus, but in some cases it is necessary to examine the fetus directly or to carry out minor procedures on him or her. These procedures can be performed by fetoscopy, in which a fetoscope (a type of endoscope, or fiberoptic viewing tube) is passed into the woman’s uterus through a small inci­sion in her abdomen.

The direct access that fetoscopy gives allows any external fetal abnormalities, such as spinal column defects, facial clefts, or limb defects, to be assessed; it also enables samples of skin or blood to be taken from the fetus for tests. By attaching special instruments to the fetoscope, the physician can perform a variety of procedures, such as transfusing blood into the fetus to treat anemia. The fetoscope also allows some types of disorders (such as obstruction of the urinary tract) to be surgically corrected.

Amniocentesis and chorionic villus sampling

Amniocentesis and chorionic villus sampling can be used to diagnose certain fetal abnormalities early enough in pregnancy for elective abortion to remain a feasible option. However, because these procedures carry a small risk of inducing miscarriage, they are recommended only when there are good medical reasons for doing so, such as when the woman is older than 35 or when there is a family history of a chromosomal abnormality.

Amniocentesis involves removing and testing a sample of the amniotic fluid that surrounds the fetus. The procedure cannot be done before about the 16th to 18th week of pregnancy because there is not enough amniotic fluid before this time.

The amniotic fluid contains fetal cells that can be examined under a microscope, which are cultured to provide chromosomes for a karyotype analysis (a preparation of the chromosomes suitable for identifying chromosomal abnormalities). It may take two to three weeks to culture a chromosome sample using a high-powered microscope, which means that results are not usually available until the 18th to 20th week of pregnancy. The amniotic fluid also contains various chemicals, the levels of which may be measured to test for other, nonchromosomal disorders of the fetus. For example, raised levels of alpha-fetoprotein may indicate a neural tube defect, such as spina bifida.

Chorionic villus sampling is another method of diagnosing fetal abnormalities due to chromosomal defects. Unlike amniocentesis, it is not suitable for detecting nonchromosomal abnormalities. In chorionic villus sampling, a small sample of tissue from the fetal side of the placenta is removed using obstetrical instruments; the cells in the sample (which are genetically identical to those of the fetus) then undergo chromosomal analysis, which can usually be done immediately. Chorionic sampling can be done as early as eight to nine weeks into pregnancy (or later, if necessary). It gives results earlier than amniocentesis and permits a safer elective abortion if this course of action is chosen.

Genetic counseling

About one child in 50 is born with a physical, metabolic, or mental defect. Many of these defects are due to an abnormality in one or more of the genes inherited from the parents. In some cases, the parents are unaware that one (or, rarely, both) of them carries a defective gene, usually studied under a high-powered microscope. Occasionally, the defect is a new one that is caused by a genetic mutation occurring during the formation of the sperm or ovum. Sometimes, however, a couple planning a family knows that one or more of their relatives have had children with a gene­tic disorder. In such cases, the couple should seek genetic counseling before their first pregnancy. The counselor can often perform tests to determine if there is a risk of a genetic disorder being passed on to the children and, if that is a possibility, may be able to quantify the risk involved. This allows the couple to make an informed decision as to whether they wish to continue with the pregnancy.

Treating infertility

Approximately one in every 10 couples finds it difficult to have children. In about 40 percent of such cases, the man is subfertile or infertile; in another 40 percent, the woman has a fertility disorder. In the remaining 20 percent, both partners have some degree of infertility. Methods employed to improve the likelihood of pregnancy include microsurgery using obstetrical instruments to repair damaged fallopian tubes in women or to reverse vasectomy in men; drugs or hormones to stimulate ovulation in women or improve male fer­tility; and in vitro fertilization (”test-tube baby”) techniques, although the success rate for this pro­cedure remains low.