CHORIONIC VILLUS SAMPLING (CVS)
CVS is a diagnostic outpatient office procedure performed under ultrasound guidance without anesthesia. Procedure-related pregnancy loss rate is 0.7%.
• The catheter is placed directly into the placental tissue without entering the amniotic cavity. Chorionic villi, which are placental precursors, are aspirated from a pregnant uterus between 10 and 12 weeks’ gestation.
• The tissue is sent to the laboratory for karyotyping. The chromosomes of the villi are almost always identical to those of the embryo.
• The procedure can be performed either transcervically or transabdominally. Since the fetus and chorionic villi are both derived from a common origin (the zygote), their karyotype is identical more than 99% of the time.
AMNIOCENTESIS
Amniocentesis is a diagnostic, outpatient office procedure performed after 15 weeks under ultrasound guidance without anesthesia. Pregnancy loss rate is 0.5%
• A needle is placed into a pocket of amniotic fluid under direct ultrasound guidance, aspirating amniotic fluid containing desquamated living fetal cells (amniocytes).
• Fetal karyotyping is performed on amniocytes. NTD (Neural tube defect) screening is performed on amniotic fluid with biochemical analysis (AFP and acetylcholinester-ase).
Amniotic
fluid
Cervix
Amniocytes
Figure I-3-1. Amniocentesis
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Chapter 3 l Obstetric Procedures
PERCUTANEOUS UMBILICAL BLOOD SAMPLE (PUBS)
This transabdominal procedure, performed under ultrasound guidance, aspirates fetal blood from the umbilical vein after 20 weeks’ gestation.
• The procedure can be diagnostic (e.g., blood gases, karyotype, IgG and IgM antibodies) as well as therapeutic (e.g., intrauterine transfusion with fetal anemia).
• Procedure-related pregnancy loss rate is 1–2%.
FETOSCOPY
A fetoscopy is a transabdominal procedure performed with a fiberoptic scope in the operating room after 20 weeks under regional or general anesthesia.
• Indications for fetoscopy include intrauterine surgery or fetal skin biopsy.
• Laser is used for coagulating placental vessels in twin−twin transfusion syndrome (TTTS). Skin biopsy may be performed for suspected fetal ichthyosis.
• Risks are bleeding, infection, membrane rupture, fetal loss.
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• The pregnancy loss rate is 2−5%.
PRENATAL DIAGNOSTIC TESTING
Table 3-1. Prenatal Diagnostic Testing
| CVS | 10-12 wks | 0.7% pregnancy loss rate |
| Placental precursor | ||
| First Trimester | 10-14 wks | 0% pregnancy loss rate |
| Nuchal T, PAPP-A | ||
| Amniocentesis | >15 wks | 0.5% pregnancy loss rate |
| Amniocytes; amniotic fluid AFP | ||
| Expanded X-AFP | 15-20 wks | 0% pregnancy loss rate |
| MS-AFP, b-hCG, estriol, inhibin | ||
| Sonogram | 18-20 wks | 0% pregnancy loss rate |
| Non-invasive anatomy scan | ||
| Fetoscopy | 18-20 wks | 3-5% pregnancy loss rate |
| Laser in TTTS, fetal biopsy | ||
| PUBS | >20 wks | 1-2% pregnancy loss rate |
| Umbilical vein blood | ||
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| Normal Pregnancy |
DIAGNOSIS OF PREGNANCY
Presumptive signs of pregnancy include amenorrhea, breast tenderness, nausea and vomiting,increased skin pigmentation, and skin striae.
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Probable signs of pregnancy include enlargement of the uterus, maternal sensation of uterinecontractions or fetal movement, Hegar sign (softening of the junction between the corpus and cervix), and positive urine or serum b-human chorionic gonadotropin (b-hCG) testing.
Positive signs of pregnancy include hearing fetal heart tones, sonographic visualization of a fetus, perception of fetal movements by an external examiner, and x-ray showing a fetal skeleton.
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