Prenatal Diagnostic Tests

Question 1

Indications for Prenatal Diagnostic Testing

1. To establish baseline information (about fetus)
2. Detect congenital abnormalities (of fetus)
3. Evaluate fetus in high risk pregnancies

Answer 1

Factors for Testing - Medical

* Have DM or gestational DM; chronic or pregnancy-induced HTN; have acute or non-acute infections; have STI’s; severe anemia; women or their partners who are carriers of genetic disorders like sickle cell or cystic fibrosis

Question 2

Factors for Testing - Demographic

* Are under 16 or over 35

* Those living in poverty; are non-White clients

* Are those w/inadequate prenatal care where it started 20 weeks >gestation

Answer 2

Factors for Testing - Maternal

* Low or high pre-pregnancy BMI

* Inadequate or excessive weight gain during

* Use of alcohol, drugs, & tobacco

Question 3

Factors for Testing - Obstetric

* h/o low birth weight infants

* preterm infant

* multi-fetal pregnancy

* Fetus in malpresentation; prior fetal loss or baby born w/a congenital anomaly

* Infant weight >4000g

* Polyhydramnios (too much) or oligohydramnios (too little)

Answer 3

Factors for Testing - Obstetric cont’d

* Decreases or absences of fetal movement

* Doesn’t know gestational age or date of LMP

* If suspect intrauterine growth restriction

* If unequal growth between 2 twins

* Gestation >42 weeks

* Experiences preterm labor

* Grand multiparity = more than 5 pregnancies

Question 4

Ultrasound - First Trimester Ultrasounds

* To estimate fetal gestational age based on measurements obtained

* Lets us confirm viability in that we can see fetal HR

* Identify need for follow-up testing & chromosome abnormalities

* Transvaginal looks up through the cervix

> Done to determine if there’s a pregnancy

Answer 4

* Ascertain if anywhere outside the uterus?

* Is there more than 1 fetus?

Question 5

Ultrasound - 2nd & 3rd Trimester Ultrasounds

* Typical transabdominal US; uterus has moved up & out of pelvis

* Have a full bladder ready

* Confirm viability & assess fetal HR

* Evalulate fetal anatomy

* Assess growth & compare growth within multi-fetal pregnancies

* Evaluate amniotic fluid volumes

Answer 5

* Determine location of placenta & umbilical cord

* Assess fetal presentation in utero

* To help guide needle placement for invasive procedures

* Using biparietal diameter, femur length, & abdominal circumference

* >32 weeks gestation is subject to major error

Question 6

Advantages of US

* Safe & clear visualization of fetus

* Non-invasive

* Results immediately available

Answer 6

Disadvantages of US

* May not identify every defect

* Consider cost & whether insurance will cover

Question 7

* Nuchal translucency US to look for ___ ?

* For CVS

* Measurement of fetus from crown to rump

* Anatomy scans are done at 18-20 weeks

Answer 7

Down syndrome

Question 8

Doppler US blood flow assessment or a color Doppler assessment

* Can assess blood flow through the umbilical artery & identify any abnormalities in diastolic flow

* 1 vein & 2 arteries

Answer 8

3D US

Question 9

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Is an aspiration of amniotic fluid from the amniotic sac for examination

Answer 9

amniocentesis

Question 10

Second Trimester

* Examine fetal cells present in amniotic fluid to identify chromosomal or biochemical abnormalities

* Could be done at 11-14 week mark

* For mothers > 35

* Determine gender to look for maternal carrier or X-linked disorders like hemophilia

* Also evaluates fetal condition if mom is sensitized to Rh+ blood, presence of amniotic infections, & to test the AFAFP in setting of MSAFP abnormalities

Question 11

Fetal Lung Maturity

* At 3rd trimester

* Recommended when non-emergent delivery is considered prior to 38 weeks gestation

* Used to reduce risk of respiratory distress in the newborn

* L/S ratio: 2 lipoproteins, lecithin & sphingomyelin, are what comprises surfactant; a 2:1 ratio is adequate

Question 12

Fetal Hemolytic Disease

* Determines fetal bilirubin levels if mom is Rh- & sensitized

* Level of bilirubin in amniotic fluid reflects RBC destruction

* Mom has created antibodies against Rh+ RBC’s

> Will attack infant RBC’s

* Only in mom’s who aren’t sensitized

* Provide RhoGAM at delivery

Answer 12

* If the infant has a fetal hemolytic disease, infant at risk for erythroblastosis fetalis or hydrops fetalis

Question 13

Blood & Fluid Screenings

* Alpha-Fetoprotein Screening

* Multiple Marker Screening

* Chorionic Villus Sampling

* Percutaneous Umbilical Blood Sampling (Cordocentesis)

Question 14

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Often done in conjunction w/AFP screening

Drawn from mother

Gather information about factors from Trisomy 18 or 21

Answer 14

Multiple Marker Screening

Question 15

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Tells us about fetal chromosomal issues or metabolic abnormalities

Can’t tell us about neural tube defects

A lot more invasive; going into the placenta

Answer 15

Chorionic Villus Sampling

Question 16

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A main protein in fetal plasma

Diffuses into fetal urine & gets excreted in amniotic fluid

Can cross the placental membranes & end up in the maternal circulation

Is how we do a blood test on mother to determine gender of baby; gets a protein from the plasma

High levels correlate w/neural tube defects like omphalocele or spina bifida

16-18 weeks gestation

Answer 16

Alpha-Fetoprotein Screening

Question 17

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Aspirating umbilical cord blood near the placenta

* Direct line to baby

Used for diagnosis & management of Rh disease or infection where mom has sensitized against her baby

Can detect infection in the fetus as we’re getting fetal blood from the cord; give RhoGAM following

Risk of fetal loss/infection; uterine infection; fetal bradycardia; could be a cord laceration, cord hematoma, or thrombosis

* Thromboembolisms could occur; ⇒ preterm labor

Answer 17

Percutaneous Umbilical Blood Sampling (Cordocentesis)

Question 18

Antepartum [Before Delivery] Fetal Surveillance

* Nonstress Test

* Contraction Stress Test

* Biophysical Profile

* Vibroacoustic Stimulation

Question 19

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Purpose: provide acute & chronic markers of fetal well-being. Normal values indicate adequate neurological function & oxygenation

* Ultrasound

* Prevent fetal injury

* Scoring system

Answer 19

Biophysical Profile

Question 20

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Purpose: used to confirm whether NST findings are reassuring & shorten time to obtain a quality NST

* Predict well-being

* Preterm responses

* 3 attempts

• Done in 1 min intervals

* Prior to about 26-28 weeks, the brain doesn’t yet know how to respond to auditory stimulation, so this wouldn’t work

Answer 20

Vibroacoustic Stimulation

Question 21

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Purpose: to assess if the fetus can tolerate uterine contractions necessary for labor

* Uterine stimulation

* Negative or Positive

* 99% reassurance

Answer 21

Contraction Stress Test

Question 22

Contraction Stress Test

Use nipple stimulation or a low dose oxytocin/pitocin

Do we see late decelerations?

Is unsatisfactory if there are <3 contractions in 10 min

> Don’t do if preterm; there’s a h/o extensive uterine surgery; if there was a premature rupture of membranes or placenta previa

> If mother shouldn’t deliver vaginally

Answer 22

* Negative if there’s no late or variable decelerations (no drops in the FHR are occurring)

* Positive if there are drops in the FHR occurring w/50% or more of the contractions; can be equivocal

Question 23

Nonstress Test

Purpose: to identify if an increase in FHR occurs in response to fetal movement, indicating adequate oxygenation

* Specialized training

* Reactive vs Nonreactive

* False positives

For 28 weeks & above

Placed on a continuous fetal monitor

Answer 23

An acceleration is an increase by 15 bpm that lasts for at least 15 sec

* Have to see 2 accelerations with or without fetal movement within a 20 min period

* A 29 week fetus who shows a 15x15 will set that as the marker for them

If fetus is 32 weeks of age or younger, looking for an increase by 10 bpm by 10 sec

If 28 weeks or less not likely to see acceleration because CNS is not developed

• Called a 15x15 or 10x10

Question 24

If we see (2) 15x15 or (2) 10x10 accelerations in that 20 minute period for under 32 weeks, is termed a reactive nonstress test

Answer 24

If these things are missing, this is a nonreactive nonstress test

* We give at least an hour on the monitor when we set up mother because fetuses have sleep cycles & typical cycle lasts up to 40 minutes

> Stimulate mother w/food to provide glucose to fetus; give a cold drink to stimulate fetus

> If this does not show anything, proceed to vibroacoustic stimulation

Question 25

Nonstress Test

Answer 25

Contraction Stress Test

Question 26

! Fetal monitoring to assess oxygenation status; monitor for signs of hypoxia

Late ___ appear (first sign)

Accelerations disappear (next sign) [i.e. 15x15 or 10x10]

Fetal ___ movement stops (see on US)

Fetal movement ceases (late sign)

Fetal ___ absent (fetus already compromised) [may have hypoxic injury]

Answer 26

decelerations

breathing

tone

Question 27

Biophysical Profile - BPP

Scored out of 10 or out of 8 (out of 8 if we exclude the NST)

“8 is great”

All done via US (except for the NST)

> Fetal ___ movements

> Gross body movements

> Fetal ___ (as simple as opening & closing of the hand)

> Amniotic Fluid Volume

Answer 27

breathing

tone

Question 28

Maternal Assessment of Fetal Movement - “Kick Counts”

* Is the maternal assessment of fetal movements

* Note patterns & changes

* Perception can vary

* Be mindful of doing kick counts during fetal sleep cycles

* Maternal rx’s can have an effect on activity