Indications Maternal age > 35 (increased risk of some chromosomal anomalies) abnormal MSS or ultrasound past history of pregnancy w...
Indications
- Maternal age > 35 (increased risk of some chromosomal anomalies)
- abnormal MSS or ultrasound
- past history of pregnancy with chromosomal anomaly or genetic disease
- either parent a known carrier of a genetic disorder or balanced translocation
- three or more miscarriages
- family history of chromosomal anomaly, genetic disorder, birth defect,
or undiagnosed mental retardation - consanguinity
- ultrasound-guided transabdominal extraction of amniotic fluid at
- 15-16 weeks gestation to identify genetic problems such as trisomies
- during 3rd trimester for assessment of fetal lung maturity
L/S ratio: if > 2:1, fetal lungs are mature enough that RDS less likely to occur
- used to quantitate amniotic fluid bilirubin concentration in Rh-isoimmunized pregnancies advantages
- screen for NTD (acetyl cholinesterase and amniotic AFP)
- more accurate genetic testing
- disadvantages
- 0.5% risk of spontaneous abortion
- results take 10-14 days,FISH (Fluorescent In Situ Hybridisation)available in 72 hours
- in women over 35 years, the risk of chromosomal anomaly (1/180) is greater than the increased risk of miscarriage from the procedure, so it
is offered routinely
.
.
Chorionic Villus Sampling (CVS)
- needle through abdomen or catheter through cervix at 10-12 weeks
- advantages
- enables pregnancy to be terminated earlier
- more rapid karyotyping, DNA tests, chromosome status, biochemical assay (results in 48 hours; do not have to wait for culture)
- increasing availability of probes to allow diagnosis of genetic abnormalities (i.e. FISH)
- disadvantages
- 1-2% risk of spontaneous abortion
- does not screen for neural tube defects (NTD)
- risk of limb injury
- poor test because of genetic mosaicism
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