Prenatal Diagnostic Tests Flashcards
Indications for Prenatal Diagnostic Testing
- To establish baseline information (about fetus)
- Detect congenital abnormalities (of fetus)
- Evaluate fetus in high risk pregnancies
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
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
Factors for Testing - Maternal
* Low or high pre-pregnancy BMI
* Inadequate or excessive weight gain during
* Use of alcohol, drugs, & tobacco
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)
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
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
* Ascertain if anywhere outside the uterus?
* Is there more than 1 fetus?
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
* 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
Advantages of US
* Safe & clear visualization of fetus
* Non-invasive
* Results immediately available
Disadvantages of US
* May not identify every defect
* Consider cost & whether insurance will cover
* Nuchal translucency US to look for ___ ?
* For CVS
* Measurement of fetus from crown to rump
* Anatomy scans are done at 18-20 weeks
Down syndrome
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
3D US
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Is an aspiration of amniotic fluid from the amniotic sac for examination
amniocentesis
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
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
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
* If the infant has a fetal hemolytic disease, infant at risk for erythroblastosis fetalis or hydrops fetalis
Blood & Fluid Screenings
* Alpha-Fetoprotein Screening
* Multiple Marker Screening
* Chorionic Villus Sampling
* Percutaneous Umbilical Blood Sampling (Cordocentesis)
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Often done in conjunction w/AFP screening
Drawn from mother
Gather information about factors from Trisomy 18 or 21
Multiple Marker Screening
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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
Chorionic Villus Sampling
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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
Alpha-Fetoprotein Screening
?
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
Percutaneous Umbilical Blood Sampling (Cordocentesis)
Antepartum [Before Delivery] Fetal Surveillance
* Nonstress Test
* Contraction Stress Test
* Biophysical Profile
* Vibroacoustic Stimulation
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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
Biophysical Profile
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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
Vibroacoustic Stimulation
?
Purpose: to assess if the fetus can tolerate uterine contractions necessary for labor
* Uterine stimulation
* Negative or Positive
* 99% reassurance
Contraction Stress Test
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
* 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
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
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
If we see (2) 15x15 or (2) 10x10 accelerations in that 20 minute period for under 32 weeks, is termed a reactive nonstress test
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
