Diagnostic amniocentesis AND Chorionic villus sampling

INDICATION

Previous child with a chromosome abnormality or genetic disorder Parent is a carrier of a balanced translocation or other structural chromosome disorder Parent is a carrier of a monogenic (ie, single gene or Mendelian) disorder Both parents are carriers of autosomal recessive disease Female parent is a carrier of a sex-linked disease Congenital anomaly on first trimester ultrasound examination Abnormal results at aneuploidy screen (eg, maternal serum analytes with/without sonographic markers of aneuploidy, cell-free DNA)

CONTRAINDICATIONS AND TIMING

CVS Maternal alloimmunization Intra uterine device (IUD) is in situ there is a risk of vertical transmission of maternal infection, such as human immunodeficiency virus (HIV), hepatitis B and C.  10 and 14 weeks of gestation CVS

Technique Genetic evaluation Transcervical chorionic villus sampling Transabdominal chorionic villus sampling  Genetic evaluation  Rapid karyotyping can be achieved within 2 to 48 hours of sampling by direct examination of cytotrophoblast (ie, direct method) since these cells have a high mitotic index and can be examined in metaphase Due to the risk of false positive results, long-term (one week) cultures of mesenchymal cells should be performed concurrently as these cells better reflect fetal, rather than the placental, genotype

Diagnostic uncertainty and misdiagnosis The false negative rate with CVS is extremely low In contrast, amniocentesis should be performed to rule out a false positive test when the mosaic karyotype is found in mesenchymal cells. If the chorionic villus sample is inadequate for both direct preparations and long-term cultures, long-term culture appears to be more reliable than a direct preparation 0.03 percent in one series of over 62,000 procedures

Post procedure care  Women may resume normal physical activity after the procedure. We generally advise them to avoid strenuous activity and sexual intercourse for 24 hours. We also inform them that some spotting is normal, but they should call for persistent bleeding, pain, fever, or other concerns.

COMPLICATIONS Total fetal loss rate Perinatal loss Loss of multiple gestation  Failure to obtain a sample Maternal cell contamination  Limb-reduction defects and oro mandibular hypo genesis Bleeding Infection  Feto maternal hemorrhage Rupture of membranes

amniocentesis Amniocentesis for prenatal genetic studies is technically possible at any gestational age after approximately 11 weeks of gestation, but is optimally performed at 15 to 17 weeks of gestation. Procedures performed before 15 weeks (ie, early amniocentesis) are associated with higher fetal loss and complication rates, including culture failure, and should be avoided Test results are available sooner when blood is the source of cellular material: 24 to 48 hours versus 7 to 10 days when amniocytes or chorionic villus cells are cultured. laboratory-related failure rates of karyotyping increase significantly with advancing gestation so that, in the third trimester, karyotyping is more likely to fail than microarray Fluorescence in situ hybridizationInterphase fluorescence in situ hybridization (FISH) provides a limited karyotype within 24 to 48 hours, but only detects aneuploidy of chromosomes 13, 18, 21, X, and Y, which are the most common causes of aneuploidy.

Evaluation of fetal demise Chromosomal abnormalities are more prevalent in stillborn than liveborn infants. Amniocentesis to obtain fetal cells as soon as possible after fetal demise is more likely to yield viable cells for analysis than tissue obtained after delivery. Use of chromosomal microarray appears to increase diagnostic yield because it does not require cell culture. Fetal lung maturity Antibiotic prophylaxis Post-procedural care DISCOLORED SAMPLES  Blood-tinged amniotic fluid green or brown pigment in second trimester amniotic fluid

COMPLICATIONS AND ADVERSE OUTCOMES — The major complications of amniocentesis are rupture of membranes, direct fetal injury, indirect fetal injury, infection, Vertical transmission Innoculation by bowel flora and fetal loss. Maternal complications related to the procedure, such as amnionitis, are rare, occurring in less than 1/1000 procedures.

Mosaicism Cell culture failure Obstetrical complications Amniocytes fail to grow in culture in 0.1 percent of samples Mosaicism  True mosaicism is defined as one or more abnormal cell lines plus a normal cell line in at least two primary cultures from the same individual; it occurs in 0.1 to 0.2 percent of pregnancies undergoing amniocentesis Pseudomosaicism (ie, an abnormal cell line confined to one culture flask) is more common, occurring in up to 8 percent of pregnancies Obstetrical complications Third trimester amniocentesis 

ANEUPLOIDY SCREENING IN MULTIPLE GESTATION  Monozygotic twins are thought to have the same Down syndrome risk per pregnancy as maternal age–matched singletons, and dizygotic twin pregnancies are thought to have twice the risk of at least one affected fetus as maternal age–matched singleton pregnancies.

●Combined test We suggest offering Down syndrome screening with the first-trimester combined test, which can provide fetus-specific risk assessment. Increased nuchal translucency at >10 and <14 weeks of gestation is a marker for Down syndrome, other aneuploidies, congenital malformations, and development of twin-twin transfusion syndrome (TTTS). Maternal serum analyte interpretation is problematic in twin pregnancies since both twins contribute to the analyte concentration and analyte levels may be affected by early loss of one or more embryos of a multiple gestation Measurement of nuchal thickness can improve the detection rate and help identify which fetus is affected

the false-positive rate of nuchal translucency screening is higher in monochorionic than in dichorionic twins because increased nuchal translucency can be an early manifestation of TTTS as well as a marker of aneuploidy in vitro fertilization affects analyte values used in Down syndrome screening and may be considered by some laboratories when calculating screening results in twins conceived by this method An additional factor complicating prenatal diagnosis of monozygotic twins is that rarely these twins have different genotypes due to fetal mosaicism or confined placental mosaicism . They can also be discordant for X-inactivation in females, differential gene imprinting, and smaller-scale genetic abnormalities, such as microdeletions

Noninvasive screening using cell free DNA Noninvasive prenatal screening for Down syndrome using cell free DNA is challenging because the fetal cell free DNA in the maternal circulation derives from each fetus. Testing is commercially available for trisomies 13, 18, and 21, although less validation data are available from twin gestations than from singletons An additional challenge in twin pregnancy is that the amount of cell free DNA contributed by each twin is lower than in a singleton pregnancy and may be quite different for the two fetuses in dizygotic twins

CVS Diagnostic testing amniocentesis Loss rate Most operators perform separate procedures on each sac for genetic studies of multiple gestations Loss rate  The risk of amniocentesis-related loss in twin pregnancies is likely increased by about 1 percent above the baseline risk of loss among twin gestations, but the exact risk is uncertain Sonographic determination of chorionicity of multiple gestations is essential prior to CVS, as chorionicity determines the number of samples that need to be obtained. If the placentas are fused and either dichorionic or of uncertain chorionicity, the tip of the aspirating device should be inserted either close to the insertion of the umbilical cord or at the placental margin, far away from the area of fusion, to minimize the possibility of sampling the same fetus twice