Click here to view next page of this article

Chorionic Villus Sampling

Indications for CVS are essentially the same as those for amniocentesis, except for analyses that require amniotic fluid rather than amniotic fluid cells. The primary advantage of CVS is that results are available much earlier in pregnancy, which decreases parental anxiety when results are normal and, when they are abnormal, allows earlier and safer methods of pregnancy termination. Earlier diagnosis may also be required for prenatal treatment (eg, prevention of female virilization in fetuses affected with 21-hydroxy-lase deficiency by administration of dexamethasone to the mother).

Placental villi may be obtained through transcervical, transabdominal, and transvaginal access to the placenta. Active infection is a contraindication to transcervical CVS. Later in pregnancy, when a fetal malformation or IUGR.

There have been three major collaborative studies comparing CVS and amniocentesis. Trials at the National Institute of Child Health and Human Development and in Canada had similar results, with more than 99% cytogenetic analysis success and total pregnancy loss rates of 0.6-0.8% in excess of amniocentesis. A European study reported an excess loss rate in the CVS group that was different both clinically and statistically from the results of the other two large needles.

Prenatal cytogenetic diagnosis is occasionally complicated by the finding of more than one distinct cell line obtained from a single chorionic villus sample. When this occurs, it may be the result of fetal karyotypic mosaicism, confined placental mosaicism, or pseudomosaicism. Fetal mosaicism represents two distinct cytogenetic cell lines in the fetus. Confined placental mosaicism is defined as two cell lines that occur only in the placenta and not in the fetus. Pseudomosaicism represents two or more cell lines that have arisen in cell culture but are not representative.

Poor pregnancy outcome and perinatal loss have been reported in association with confined placental mosaicism. The utility and method of antepartum.

There have been reports of an association between CVS and limb reduction and oromandibular defects. Cavernous hemangiomas have also been reported. The risk for these anomalies is unclear. According to the World Health Organization, the global 10-year experience with CVS reveals an incidence of limb reduction defects.

Amniocentesis

Amniocentesis for prenatal diagnostic testing is usually offered between 15 and 20 weeks of gestation. Under ultrasound guidance, a 20-22-gauge spinal needle is passed into the amniotic fluid. The initial aspirate of 1-2 mL.

Amniocentesis with twins is possible in 95% of pregnancies. Amniotic fluid is aspirated from the first sac. Before the needle is removed, 2-3 mL of indigo carmine (methylene blue is not recommended) diluted 1:10 in bacteriostatic.