M3. Indication of cytogenetic test

The more common forms of aneuploidy that are sufficient viable to survive to term include:

• Trisomy

  • 13, 18, and 21

• Sex chromosome aneuplodies

  • 45, X

  • 46,XXY (relatively benign)

What are some prenatal cytogenetic tests?

• Percutaneous umbilical blood sampling (PUBS)

• Chorionic Villus Sampling (CVS)

• Amniocentesis

(all are invasive and could cause risk of miscarriage, only if high risk for chromosome abnormality)

What are transvaginal scans?

Specially designed probe transducers are used inside the vagina to generate sonogram images.

• Most often used during the early stages of pregnancy

What are standard US?

Traditional ultrasound exam which uses a transducer over the abdomen to generate 2-D images of the developing fetus.

What is a doppler US?

This imaging procedure measures slight changes in the frequency of the ultrasound waves as they bounce off moving objects, such as blood cells.

What a 3D US?

Uses specially designed probes and software to generate 3-D images of the developing fetus.

What is AFP?

A plasma protein initially produced by the fetal yolk sac in small quantities, then produced by the fetal liver in larger quantities

When is MSAFP done?

Most often done between 15 and 18 weeks after the last menstrual period, but first detectable around 12 weeks

How much does MSAFP increase/decrease from gestation until birth?

• About 15%/week until 25th week peak

• Starts to decline at 26 weeks

• At birth, <2 ng/mL

High levels of AFP may suggest …

The developing baby has a neural tube defect due to leakage of fetal plasma into the amniotic fluid

Low levels of AFP may suggest …

• Trisomy 21( Down syndrome)

• Trisomy 18 (Edwards Syndrome)

• Another type of chromosome abnormality

What is anencephaly?

The neural tube fails to close properly at the base of the skull

What is spina bifida?

The neural tube fails to close properly at the bottom of the spine

What factors can affect MSAFP?

• Gestational age (although could be corrected s/p US)

• Mother’s age

• Maternal weight

  • Lower levels: Obese and insulin dependent diabetics

• Maternal ethnicity

  • Higher levels: African American

  • Lower levels: Asian

• Multiple fetuses

What is hCG?

Human chorionic gonadotropin, a hormone produced within the placenta

When can hCG first be detected? When is it’s peak?

First detection:

• Blood test: 11 days s/p conception

• Urine test: 12-14 days s/p conception

Peak:

• 8-11 weeks then decrease after

A low hCG can indicate …

• Miscalculation of pregnancy dating

• Ectopic pregnancy

• Possible miscarriage

• Trisomy 18

A high hCG can indicate …

• Miscalculation of pregnancy dating

• Multiple pregnancies

• Molar pregnancy

• Trisomy 21

What is uE3?

Unconjugate estriol, an estrogen produced by both the fetus and placenta

A low level of uE3 can indicate …

Trisomy 18 or 21

What is inhibin A?

A protein produced by the placenta and ovaries

A high inhibin-A level can indicate

Trisomy 21 (inhibin-A)

What does a low PAPP-A level indicate?

Trisomy 21 (PAPP-A)

What are some indications for prenatal cytogenetic test for AFP

• Advanced maternal age

• Positive family history

• Abnormal US scan result

• Positive result from 1st trimester screening

• Positive result from 2nd trimester maternal serum screening