What We Offer

Prenatal Diagnosis via Amniocentesis and Chorionic Villus Sampling (CVS)

Many inherited conditions can be diagnosed prenatally, via CVS or amniocentesis. These procedures have identified chromosomal abnormalities, such as Down's syndrome, and neural tube defects, such as spina bifida. Recently, however, explosive growth in DNA testing technology has made it possible to detect hundreds of additional genetic disorders, including Tay-Sachs, cystic fibrosis, Duchenne muscular dystrophy, and sickle-cell anemia, to name a few.

We employ molecular technologies that allow us to achieve results for certain conditions such as for Down Syndrome usually within one day after the procedure.

Amniocentesis

Amniocentesis was the first method developed for prenatal diagnosis. It is usually performed between 15 and 20 weeks from the beginning of the last menstrual period. Under the guidance of ultrasound, a very fine needle is inserted through the woman's abdominal wall and into the uterus. Approximately one ounce of fluid is withdrawn and sent to the laboratory for analysis. In experienced hands, genetic amniocentesis is a very safe test. A limitation of amniocentesis is that reassurance or diagnosis of problems does not occur until the second trimester.

Chorionic Villus Sampling (CVS)

Chorionic villus sampling or CVS is the first-trimester procedure for prenatal diagnosis of fetal chromosomal and genetic disorders, usually performed 11 to 13 weeks from the beginning of the last menstrual period. The procedure can be done one of two ways. In singleton pregnancies, most of the time the patient is placed in stirrups, and a speculum is inserted just as for a Pap smear. A small catheter (similar to a straw) is passed painlessly through the cervix and maneuvered into the placental tissue under ultrasound guidance. A syringe is then attached to the end of the catheter, and a very small amount of tissue is aspirated. In some cases (about 30% of the time), depending upon the position of the placenta, a needle may be inserted trans abdominally and maneuvered into the placenta (not the fluid). In either case several milligrams of tissue are sent to the lab. Tests can then be performed for chromosomal (e.g. Down Syndrome) molecular diagnosis (such as cystic fibrosis, or FISH for a quick read of chromosomes such as Down Syndrome), or enzymatic analysis (for some biochemical disorders).

We commonly perform CVS for diagnosis of singleton pregnancies at elevated risk for birth defects; for diagnosis in multiple pregnancies prior to reduction, to help ensure the health of fetuses remaining after the procedure; and for patients who have undergone preimplantation genetic diagnosis (PGD) with in vitro fertilization, who need post-implantation confirmation of the normalcy of the fetus.

Laboratory Testing

There has been a virtual explosion in the sophistication of laboratory testing available both for screening tests as described above and for direct evaluation of fetal health from CVS, amniocentesis, fetal skin, and fetal tissues.

The traditional test is the karyotype in which cells from tissue specimens are cultured and then organized into groups based upon their size and the centromere which connects a "long" and a "short" arm. There are normally 46 of these – actually 23 pairs. Each of us normally inherits one of each of our parent's chromosomes which pairs up with one from the other parent. When we make our sperm or eggs, one of each of our pairs goes into the sperm or egg. The first 22 pairs are independent of our gender. The last pair, the sex chromosomes, determines gender. Women have two X chromosomes; men have one X and one Y.

There are 23 pairs of chromosomes. The first 22 are numbered and one of each pair comes from each parent. The last pair are the sex chromosomes. Women have 2 "X" chromosomes, and men have one "X" and one "Y."

Unfortunately, mistakes sometimes happen. The most common scenario is that in the process of creating eggs for fertilization, the splitting of one of the mother's pair doesn't occur such that the egg has two copies instead of one. Then with fertilization, the embryo/fetus has three instead of two.

Below are two karyotypes. The first is of a male with Trisomy 21 more commonly known as Down Syndrome. The second karyotype below is a female with Trisomy 18 – a condition with a very high mortality rate and severe disabilities in surviving infants.

Trisomy 21

Trisomy 18

Because our patients are "average New Yorkers" who want their answers yesterday, we also run molecular testing with a technique called fluorescent in situ hybridization (FISH) that gives rapid answers for chromosome 21 (Down Syndrome), trisomies 13 and 18, and the sex chromosomes looking for abnormalities but which gives gender as a byproduct. The two figures below show a normal male. The first picture has two copies of Chromosomes 18, one "X" and one "Y." The second shows two copies of chromosomes 13 and 21.

 

The emerging laboratory technique of microarrays is used when more precise identification of additions or deletions of material are needed. Microarrays can identify changes far too small to be seen on karyotype. We anticipate that eventually microarrays will replace karyotypes. For the moment, however, there are still numerous instances in which deletions or additions are seen for which there is no clinical information as to whether they are clinically significant or not. Thus, it is not yet ready for routine use on everyone, and the technology is expensive. Below are array depictions of a normal female – 2X chromosomes and no Y chromosomes. The second shows three copies of chromosome 21.

Fetal Tissue Sampling

Tests utilizing the DNA in fetal tissues have made possible via CVS the diagnosis of disorders such as Duchenne muscular dystrophy. Sometimes, however, DNA tests cannot give a definitive answer, and the only way to get the answer is by obtaining a piece of fetal muscle, or liver. Over the past 20+ years, we have performed more fetal muscle biopsies than anyone else, worldwide.

Similarly, some skin abnormalities and certain chromosomal abnormalities can only be diagnosed by obtaining a piece of fetal skin. Fetal skin biopsy is the optimal way to evaluate ambiguity that occasionally arises in the interpretation of amniocentesis data. These biopsies are performed without a hospital stay, and under ultrasound guidance.

Fetal Therapy

The diagnosis of a serious disorder in a fetus is a devastating event for all involved. In many cases, there may be little that medicine can offer, aside from help in preparing for the birth of child with special needs, or the option to terminate the pregnancy. In some situations, however, there is another alternative: treating the disorder before birth.

We can also provide you with world-class expertise in this area. Dr. Evans:

• •developed the first method for preventing a congenital defect before birth (congenital adrenal hyperplasia);


• •performed the first successful stem cell transplant to cure a baby with SCIDS (the "bubble babies");


• •was a member of the team that did the first successful open fetal surgery (for congenital diaphragmatic hernia); and


• •is one of the most experienced at performing fetal shunt procedures, such as for obstructed fetal bladders. We work with colleagues all over the country to provide cutting-edge therapies in pregnancies with correctable problems.

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