4.21 - birth defects

Question 1

Explain what a congenital birth defect is and indicate how common birth defects are

Answer 1

congenital defect is any physical anomaly which is recognizable at birth
-1 in 33 babies in the US are born with birth defects each year, leading cause of death in first year of life.

Question 2

Describe the three major categories of birth defects and be able to provide and identify examples of each

Answer 2

1. chromosomal defects - too many or too few chromosomes (aneuploidy)
   –> ex: trisomy 21 (down syndrome), trisomy 13 or 18
2. Single gene defects
   –> ex: achondroplasia (form of dwarfism), cystic fibrosis, hemophilia
3. Environmental factors - teratogens

Question 3

Define teratogen

Answer 3

environmental substances that can cause birth defects
–> ex: alcohol, certain drugs/medications, infections

Question 4

*Describe actions that can be taken to reduce the risk of birth defects

Answer 4

• consult genetic counselor if birth defects are present in family history
• avoid smoking, drinking alcohol, using drugs
• STD screening
• take multivitamin with folic acid (recommendations vary from 400 mcg to 4mg)

Question 5

Explain why folic acid is necessary during pregnancy.

Answer 5

folic acid is necessary for DNA synthesis, DNA repair, and DNA methylation, and it acts as a cofactor in biological reactions
- especially important for rapid cell division and growth, as in infancy and pregnancy
- folic acid can help prevent some major birth defects of the baby’s brain and spine (ancephaly and spina bifidia) by 50 to 70%

Question 6

Indicate when neural tube formation occurs and the consequences of malformation (anecephaly and spina bifidia)

Answer 6

occurs between 15-28 days of development (counting from fert)
-often before a woman knows she is pregnant, defects attributed to environmental and genetic factors

Question 7

*anencephaly

Answer 7

-upper part of neural tube does not close all the way
-baby is born without parts of brain and skull

Question 8

*spina bifidia

Answer 8

-can happen anywhere along spine where lower part of neural tube does not close all the way
-causes physical and mental disabilities that range from mild to severe

Question 9

Describe the four basic methods that can detect birth defects prenatally (during pregnancy)

Answer 9

-blood tests
-ultrasound
-chorionic villus sampling
-amniocentesis

Question 10

Explain what non-invasive prenatal testing (NIPT) is, when it is done, and what it can tell you. Include cell free fetal DNA in your discussion

Answer 10

-done as early as 7wks
cell-free fetal DNA:
-primary source in maternal circulation is thought to be apoptosis of placental cells
-most reliably used for sex determination
-most commonly used to diagnose trisomy 13, 18, 21

Question 11

Describe the goals of first, second, and third trimester ultrasound

Answer 11

first trimester:
-establish dates of preg
-detect heartbeat by 7 wks from LMP
-detect fetal movement (7-8wks)
-determine number of fetuses
-diagnose ectopic preg. or miscarriage
second trimester:
-examine fetal anatomy for presence of abnormalities
-discover sex of fetus (~14 wks)
third trimester:
-monitor fetal gowth
-check amount of amniotic fluid
-determine position of fetus and placenta

Question 12

Distinguish between chorionic villus sampling and amniocentesis. Explain how and when they are done, and what they can detect

Answer 12

CVS - checks cells in placenta for chromosome abnormality bc they are the same as the placenta
amniocentesis - tests amniotic fluid from around baby in the uterus
–
CVS
- fetus position in uterus determines which procedure is used (transcervical vs transabdominal)
-performed between 10-12 wks from LMP (placenta fully functional by this time)
-sample of placental tissue is taken under US guidance - it contains same genetic material as fetus to be test for defects
-doesn’t provide info on neural tube defects
–
amniocentesis
-performed between 15th and 20th weeks from LMP (when volume of amniotic fluid is maximized relative to size of fetus)
-sample of amniotic fluid that surrounds the fetus is taken under US guidance
-amniotic fluid contains - cells shed by fetus and alpha-fetoprotein (indicator of neural tube defect)
-provides info about neural tube defects, chromosomal abnormalities, and some other genetic defects

Question 13

Trisomy 18 cannot be detected by:
a. amniocentesis
b. embryo biopsy with Next Gen Sequencing
c. first trimester US
d. Non-invasive prenatal testing

Answer 13

can be detected by: NGS
answer: c i think?

Question 14

trophectoderm of a mosaic blastocyst has some cells that are 47, XY, +21 and some cells that are 46, XY. The inner cell mass if 46, XY. Later in the pregnancy, cells in the amniotic fluid will be:

Answer 14

46, XY

Question 15

Explain why CVS and amniocentesis are generally recommended for women over the age of 35 or any woman with family history of chromosomal problems or history of prior births in which a chromosomal problem was found.

Answer 15

because the percent chance of having a live-born baby with down syndrome increases after age 35

Question 16

Provide arguments for and against prenatal screening

Answer 16

In favor:
-pursue potential interventions that may exist
-begin planning for child with special needs
-start addressing anticipated lifestyle changes
-identify support groups and resources
-make decision about carrying child to term
Against:
-parents should be accepting of results regardless of outcome
-making decision about carrying child to term is not an option because of personal, moral, or religious reasons
-testing may pose risk of harming developing baby

Question 17

Explain what newborn screening is, when it is done, and why it is done

Answer 17

-every state routinely screens newborns before they leave the hospital for certain genetic, metabolic, hormonal, and functional disorders
-most birth defects have no immediate visible effects on a baby but, unless detected and treated early, can cause physical problems, mental retardation and, in some cases, death
-except for hearing screening, all newborn screening tests are done using a few drops of blood from newborn’s heel

Question 18

Explain what PKU is and how it is treated

Answer 18

phenylketonuria
-babies cannot process phenylalanine (amino acid found in nearly all foods)
– not a problem during pregnancy since mother processes phenylalanine
-affects about 1 9n 25,000 babies
-w/o treatment, phenylalanine builds up in blood stream and causes brain damage and mental retardation
-treatment is a low-phenylalanine diet that needs to be followed throughout infancy, childhood, adolescence, and generally, for life