Prenatal Diagnostic Tests- Maternal (OB) Nursing
This post will be covering the prenatal diagnostic tests that nursing students will need to know during their Maternal (OB) rotations. The following diagnostic tests will be covered
- Ultrasound
- Alpha-fetoprotein screening
- Chorionic villus sampling
- Amniocentesis
- Percutaneous umbilical blood sampling (PUBS)
- Nonstress test
- Contraction stress test
- Biophysical profile
Once you are done reading the info in this post, you can download this free PDF cheat sheet/study guide that has all the important information you need to know as a nursing student. You can download them onto your devices or print them out to add to your nursing binder.
Also, be sure to check out these other topics in Maternal (OB) Nursing:
Nursing Care of the Postpartum Mother
Labor and Delivery Complications
Ultrasound
Allows observer to detect fetal heartbeat, fetal breathing activity, and fetal body movement
3-D images can be captured for greater detail
Transvaginal ultrasound during the first trimester
- Gestational age can be configured by measuring the crown-rump length of the embryo
Transabdominal ultrasound during the second and third trimester
- Fetal anatomy is examined to identify any defects
Alpha-fetoprotein screening
Abnormal levels of AFP are associated with serious fetal anomalies
It is a screening; therefore additional testing will need to be done to determine the issue
Causes of increased AFP include
- Trisomy 21 (Down Syndrome)
- Anencephaly
- Spina bifida
Offered between 16-18 weeks gestation
Requires a sample of maternal blood
Chorionic Villus Sampling (CVS)
Used to diagnose fetal chromosomal, metabolic, or DNA abnormalities
Performed between 10-13 weeks
Transcervical-
- Flexible catheter is inserted through the cervix and a sample of chorionic villi is aspirated
Transabdominal-
- Needled is inserted through the abdominal and uterine wall to obtain the sample
Patient should rest for several hours after the procedure
Patient should monitor for heavy bleeding or passage of amniotic fluid, tissue, or clots- could indicate miscarriage
Cervical or vaginal infection is a contraindication
Rh sensitization can occur. All unsensitized Rh negative women should be given RhoGAM after the procedure.
Amniocentesis
Aspiration of amniotic fluid from the amniotic sac
Can be performed in the second and third trimester
Second trimester
- Used to examine fetal cells present in amniotic fluid to identify chromosomal or biochemical abnormalities
- Used to diagnose amnionitis
Third trimester
- Used to determine fetal lung maturity and fetal hemolytic disease
- Lecithin/sphingomyelin (L/S) ratio is used to estimate fetal lung maturity
- L/S ration greater than 2:1 indicates fetal lung maturity
- Phosphatidylglycerol (PG) and phosphatidylinositol (PI) are also tested to ensure lung maturity
Procedure:
- Patient is positioned in a supine position with a wedge under one buttock.
- Ultrasound used to locate fetus and placenta
- Local anesthetic
- 3-4-inch, 20-21 gauge needle inserted
- Approximately 20 mL is aspirated (first 1-2 mL is discarded to avoid contamination)
- Electronic fetal monitoring for 30-60 minutes after
- Patient can resume normal activities after 24 hours
- RhoGAM for unsensitized Rh negative women
Small risk for infection and fetal death (spontaneous abortion)
Percutaneous umbilical blood sampling (PUBS)
Aspiration of fetal blood from the umbilical cord needed for karyotype
Ultrasound to identify fetus, placenta, and umbilical cord
Needle is inserted through abdomen into uterus and sample is taken
Risks include
- Fetal death
- Infection
- Cord laceration
- Preterm labor
- Premature rupture of membranes
RhoGAM given to unsensitized Rh negative women
Antepartum fetal surveillance
Nonstress Test
Identifies whether an increase in fetal heart rate occurs when the fetus moves. This activity indicates adequate oxygenation
Electronic fetal monitoring is applied for the test
Results are either reactive (reassuring) or nonreactive (nonreassuring)
| Reactive (reassuring) | Two fetal heart rate accelerations within a 20-minute period At least 15 beats above baseline |
| Nonreactive (nonreassuring) | Tracing does not demonstrate characteristics for reactive tracing within 40 minutes or longer |
Fetal sleep cycles are a common reason for a lack of fetal movement
Contraction Stress Test
Oxytocin challenge test (OCT)
May be done if NST is nonreactive
Nipple stimulation can be used to stimulate oxytocin release
Lace decelerations and loss of variability may indicate fetal hypoxia and fetal acidosis
Contraindications:
- Preterm labor
- Preterm membrane rupture
- Placenta previa
- History of uterine surgery
Procedure:
- External electronic fetal monitoring is applied
- 3 contractions of 40 seconds each within a 10-minute period are needed
- Nipple stimulation of IV low-dose oxytocin can be used
Results:
- Negative (reassuring): no late or variable decelerations
- Positive (nonreassuring): late decelerations follow 50% or more of contractions
- Equivocal-suspicious: intermittent late or significant variable decelerations
- Equivocal-hyperstimulation: fetal heart rate decelerations occur in the presence of excessive contractions
- Unsatisfactory: fewer than 3 contractions within 10 minutes or tracing cannot be interpreted
Biophysical Profile
5 parameters are assessed
- Nonstress test
- Fetal breathing movements
- Fetal tone
- Amniotic fluid volume
- Gross fetal movements
A scoring technique is used to quantify the data
Each parameter contributes 0 or 2 points out of 10 total points
0-worst; 10-perfect
8/10-10/10= reassuring
4/10 or less= nonreassuring
| 2 points- present | 0 points- absent | |
| Nonstress test | Reactive | Nonreactive |
| Fetal breathing movement | ≥1 episode of rhythmic fetal breathing movement of 30 seconds or more within 30 minutes | Absent fetal breathing movements |
| Gross body movements | ≥3 trunk movements within 30 minutes | ≤2 trunk movements in 30 minutes |
| Fetal tone | ≥1 episode of fetal extremity extension with return to flexion; opening and closing hand within 30 minutes | Absence of flexion; extension with return to partial flexion |
| Amniotic fluid volume | At least one pocket of fluid measuring 2 cm in two planes perpendicular to each other | Amniotic fluid does not meet criteria |
I hope this was helpful for all the nursing students out there in their OB rotation.
If you have any questions be sure to reach out to me. I’m here to help. 🙂
Happy Nursing!