Chapter 11: Ultrasonography Flashcards
Ultrasonography
use of high-frequency sound waves to detect differences in tissue density and visualize outlines of structures in the body
-first trimester, used to confirm the viability and age of the pregnancy, determine the number, size, and location on gestational sacs, identify uterine abnormalities (and rule out ectopic pregnancies), and locate presence of an intrauterine contraceptive device
-FHR activity can be observed as early as 6 to 7 weeks via real-time echo sonography
-during second and third trimesters, used to confirm fetal viability and gestational age, fetal growth, AFV, placental location and maturity, and assess uterine fibroid tumors and CL
>ultrasound is an essential component of the biophysical profile and fetal Doppler studies
Kick Counts
counting fetal movements or “kick counts” is a primary method of fetal surveillance
-easy to perform, readily available to the woman, and has so cost
-instructed to lie on her side and count the number of times that she feels the fetus move
>2 Major Methods:
1. first method is done while the woman lies on her side. She counts and records 10 distinct movements in a period of up to 2 hours. Once 10 movements have been perceived, the count may be discontinued
2. second method, patient counts and records fetal movements for 1 hour three times per week. The count is to be considered reassuring if it equals or exceeds the woman’s previously established baseline
Doppler Ultrasound Blood Flow Studies (Velocimetry)
used to study blood flow in the umbilical vessels of the fetus, placental circulation, fetal cardiac motion, and maternal uterine circulation
-useful in managing pregnancies at high risk because of hypertension, diabetes mellitus, intrauterine growth restriction (IUGR), multiple fetuses, or PTL
>a noninvasive Doppler wave measures the velocity of red blood cell movement through the uterine and fetal vessels
-assessment of the blood flow through the uterine vessels is useful in determining vascular resistance in women at risk for developing placental insufficiency
>decreased velocity= poor neonatal outcome
Fetal Biophysical Profile (BPP)
noninvasive “fetal physical examination” that is more accurate in predicting fetal well-being than any physical assessment
- combines electronic FHR monitoring with ultrasonography to evaluate fetal well being
- fetus responds to central hypoxia by alterations in movement, muscle tone, breathing, and heart rate patterns; finding of normal fetal biophysical parameters indicates that the CNS is functional and therefore the fetus is not hypoxemic
- based on 30 minute time period
- has 5 components:
1. nonstress test (NST)
2. fetal breathing movements (one or more episodes of rhythmic fetal breathing movements for 30 seconds)
3. fetal movement (three or more discrete body or limb movements)
4. fetal tone (one or more episodes of extension of fetal extremity with return of flexion, or opening or closing of hand)
5. Determination of the amniotic fluid volume
Nonstress Test (NST)
involves the use of electronic fetal monitoring (EFM) for approximately 20 minutes
-based on that normal fetus moves at various intervals and that the CNS and myocardium responds to movement
-response is demonstrated by an acceleration of the FHR
>loss of heart rate activity is associated with a fetal sleep cycle but may result from any cause of CNS depression including fetal hypoxia, acidosis, and some congenital anomalies
-32 to 34 weeks is appropriate age for reactivity to occur
-acceptable criteria: FHR acceleration of 15 bpm that lasts for 15 seconds
-for preterm: a FHR acceleration of 10 bpm that lasts for 10 seconds is acceptable at 32 weeks
Preparing the Patient for A Nonstress Test
- explains procedure and asks to void
- semi-fowlers or lateral tilt position
- nurse performs Leopold maneuvers to determine fetal position and to guide proper placement of the external fetal heart ultrasound transducer (U/S) and tocodynamometer (toco)
- nurse applies the U/S and toco on maternal abdomen and obtains baseline vital signs
- tracing then observed for evidence of FHR accelerations of at least 15 bpm above the baseline HR; during this time the patient may or may not be aware of fetal movement
Results for A non-stress test
-in a term fetus, at least 2 FHR accelerations sustained for at least 15 seconds (from beginning to end of the acceleration) should occur over a 20 minute time period =”reactive test”
-test may be extended for another 40 minutes if needed
-for preterm, reactive= 2 or more FHR accelerations at least 10 bpm above the baseline occur; the accelerations must last for more than 10 seconds within a 20 minute period; testing time may be increased to 60 to 90 minutes
>if criteria not met = “nonreactive”; this should indicate further evaluation with a contraction stress test or a biophysical profile (BPP)
>”unsatisfactory”= inadequate fetal activity or if the data cannot be interpreted
Selected Indications for Nonstress Testing/ Biophysical profile
> Maternal:
- hyperthyroidism (poorly controlled)
- trauma/bleeding
- diabetes mellitus (type 1 or 2)
- chronic renal disease
- prior stillbirth or intrauterine fetal demise (IUFD)
- hemoglobinopathies
- cyanotic heart disease
- systemic lupus erythematosus
- hypertensive disorders
> Pregnancy-related:
- intrauterine growth restriction (IUGR)
- polyhydramnios
- oligohydramnios
- multiple gestation
- isoimmunization
- post-term gestation (greater than 42 weeks)
- decreased fetal movement
- hypertensive disorders
Acoustic (sound) Stimulation/ Vibroacoustic (vibration and sound) Stimulation
may be used as an adjunct to the NST to elicit an acceleration of the FHR
-a handheld instrument such as an artificial larynx is positioned on the maternal abdomen near the fetal head (Leopold maneuvers), and a low-frequency vibration and a buzzing sound are emitted
-stimulus applied for 1 to 2 seconds in an attempt to awaken the fetus and may ne repeated up to 3 times with a 1-minute rest period between attempts
>once a fetal response is achieved, no additional stimulus
>fetus showing no response= neurologically compromised or acidotic and requires further evaluation
Contraction Stress Test (CST)
evaluates FHR response to uterine contractions
-nurse uses electronic fetal monitor to obtain a baseline FHR tracing for 20 minutes; if spontaneous uterine contractions do not occur during this time, uterine stimulation is produced though IV oxytocin infusion or patient nipple self-stimulation until three contractions of at least 40 seconds duration occur within a 10 minute frame
>CSTs evaluated according to the presence or absence of late FHR decelerations
-Test is negative= no evidence of late or significant variable decelerations
-positive= (abnormal) there are late decelerations with contractions, even if the frequency is less than three in 10 minutes
Electronic Fetal Heart Rate Monitoring (EFM)
uses electronic techniques to give an ongoing assessment of fetal-well being
- provides info related to response of the fetal HR in the presence or absence of uterine contractions
- internal or external
Results of a contraction stress test
If the contraction test results turn out as abnormal (positive) then it is called the positive test which means that there are chances for the baby to have problems during normal delivery. In a positive test results case, the heart rate of the baby decelerates and remains slow even after the contractions
