2025 – PAGE 92 – OB/GYN AND SOME STDs

CHORIONIC VILLUS SAMPLING

A chorionic villus sampling is a fetal karyotype obtained from a placental biopsy. This has to do with CHROMOSOMES. This is the test that is most helpful for early detection (usually around 12 weeks) of any genetic/cytogenetic abnormalities you’re concerned about. For very high-risk pregnancies, the test may even be considered in the first trimester.

MNEMONIC: “CHROMOSOMIC” Villus Sampling. Also, imagine standing outside of a CVS at 12 midnight and craving a bag of chips. They’re closed, so throw a DOZEN EGGS at the CVS in anger (midnight and eggs representing 12 weeks).

PEARL: “CHROMOSOMIC” Villus Sampling has to do with chromosomes, so it SHOULD NOT be performed for suspected neural tube defects. (Those are usually due to a folate deficiency.)

AMNIOCENTESIS

An amniocentesis screening is offered at 15–18 weeks but may be performed at the very beginning of the 2nd trimester or after 12 weeks for high suspicion or concern. Like “CHROMOSOMIC” Villus Sampling, this helps look for identifiable genetic issues. This test can also help identify neural tube defects (via AFP levels leaked into the amniotic fluid from the neural tube defect).

* There’s really only one 3^rd trimester indication for amniocentesis: to assess fetal lung maturity.

MATERNAL SERUM TRIPLE SCREEN AND QUADRUPLE SCREEN

The maternal serum triple screen and quadruple screen are other 2^nd trimester options and are done with a simple serum sample. They screen for DOWN’S SYNDROME but can also help with screening for abdominal wall issues and even some renal anomalies. For the test, they would only expect you to know what pattern of lab values is considered positive for Down Syndrome (Trisomy 21). The screen is positive for DS if the following pattern is present:

• LOW AFP: Low = “Down” = Down Syndrome
• LOW Unconjugated EstrioL = “estrioLow”
• HIGH HCG Subunit
• HIGH InhibinA: This is part of the quadruple screen. HIgh inHIbin

FIRST TRIMESTER SCREENING OPTIONS FOR DOWNS SYNDROME

First trimester screening options for Down’s syndrome include:

• ­Chorionic Villus Sampling
• ­HCG subunit: High. This is usually done along with an ultrasound to look for nuchal translucency.

NON-STRESS TEST

A non-stress test measures fetal heart rate in response to fetal movements and is used as a measure of the “integrity of the fetal nervous system.” If a mom says that her baby is not moving, GET A NON-STRESS TEST.

• ­REACTIVE: GOOD
• ­NONREACTIVE: That’s BAD. If this occurs, get a Biophysical Profile.
• ­PEARL: A non-stress test has NOTHING to do with maternal contractions.