Ultrasonography in Pregnancy Clinical management guidelines for Obstetrician-Gynecologists Number...

Ultrasonography in Pregnancy

Clinical management guidelines forObstetrician-Gynecologists

Number 58, December 2004

Background Instrumentation : real-time, 2-dimensional image sector or convex array abdominal transducer 3~7 MHz (vaginal transducer: 5~9 MHz) linear and circumference measurement store the images : thermal index- tissue temperature mechanical index- microscopic gas bubbles : 3-dimension – advantage ↓

Type of examinations ; standard limited specialized ( during the second & third trimesters) -first trimester obstetric ultrasonography is distinct from this

<Standard Examination> : fetal presentation, amniotic fluid volume cardiac activity, placental position, fetal biometry anatomic survey, and uterus & adnexa : after 16~20 weeks of gestation : can be difficult to visualize because of fetal size, position, movement, abdominal scar, increased maternal wall thickness

Head and neck cerebellum choroid plexus cisterna magna lateral cerebral ventricles midline falx Chest cadiac exam: 4-chamber if feasible: both outflow tract

Abdomen stomach (presence,size,situs) kidneys, bladder umbilical cord vessel number & insertion site into fetal abd. Spine C-,T-,L-,S-spine Extremities legs ans arms Sex evaluation of multiple gestation

<Limited Examination> : when a specific question requires

investigations ex) fetal heart activity in a bleeding patient fetal presentation in a laboring patient

<Specialized Examination> : anomaly is suspected on the basis of history, biochemical abnormalities or clinical evaluation, or suspicious results from standard, limited exam

: fetal Doppler, biophysical profile, fetal echocardio -graphy, additional biometric studies

: by an operator with experience and expertise

<First-Trimester Ultrasonography> Indications : the presence of IUP suspected ectopic pregnancy and H-mole the cause of vaginal bleeding pelvic pain, estimate gestational age evaluate multiple gestations cardiac activity , pelvic mass, uterine abnormality villus sampling, embryo transfer, IUD remove

Imaging Parameters : transvaginal, transperineal > transabdominal 1. presence of a G-sac in uterus or adnexa →evaluates a yolk sac or embryo →CRL check (gestational age, more accurate) if, without these finding- R/O ectopic pregnancy

2. cardiac activity – when embryo > 5 mm

3. fetal number (amnionicity, chorionicity) 4. uterus – presence, location, size of leiomyoma adnexal masses fluid collection of PCDS

<Second-Trimester Ultrasonography> Indication : estimation of gestational age evaluation of fetal growth vaginal bleeding incompetent cervix abdominal and pelvic pain fetal presentation multiple gestation

amniocentesis uterine size pelvic mass H-mole cervical cerclage placement ectopic pregnancy fetal death uterine abnormality biophysical evaluation

polyhydramnios or oligohysramnios abruptio placentae fetal weight, presentation in preterm labor abnormal serum screening value follow up fetal anomaly placeta previa previous congenital anomaly fetal condition

Imaging Parameters 1. fetal cardiac activity (abnormal rate or rhythm) fetal number (chorionicity, amnionicity, size) AFV (increased, decreased) genitalia

2. qualitative or semiqualitative AFV (amniotic fluid index, deepest pocket)

3. placenta (location, appearance, relationship to the internal cervical os) umbilical cord vessel number

4. assess gestational age by BPD, AC, FL fetal growth abnormality, IUGR, macrosomia BPD- thalami and cavum septi pellicidi level outer edge~ inner edge head circumference (more reliable) head circumference- outer margin of calvarium FL- after 14 weeks accurately femoral diaphysis length AC-umbilical vein, portal sinus, stomach level at the skin line estimate fetal weight (IUGR, macrosomia)

5. Interval measurement shoud be evaluated no less than 2 weeks

6. maternal uterus and both adnexa (leiomyomata, adnexal masses) not possible to image the ovaries

Ultrasound Facility accreditation : physician- familiar with the anatomy, physiology, and pathophysiology of the pelvis, the pregnant uterus, and the fetus : undrego specific training regularly review, update their expertise

: physician are responsible for the quality and accuracy of ultrasound examinations performed in their names

Documentation : appropriate documentation of fetal biometry, maternal and fetal anatomy → clinical assessment & decision making : use preprinted template (biometry & anatomy)

: image stere- thermal paper videotape

Quality control, Performance improvement, safety, and Patient education : quality control- careful recordkeeping reliable archival of report & image clinical correlation with outcome : transducer- microbial transmission (transabdominal- wiping) (endovaginal- cover) : practitioner- update and review their skill counseled the limitation of ultrasound

Clinical Consideration and Recommendations How safe is ultrasonography for the fetus? : safe but, cannot be completely innocuous : when there is a valid medical indication the lowest possible ultrasonic exposure setting casual use should be avoided : physical effect- mechanical vibration increased tissue temperature

Should all patients be offered ultrasonography? : for example, 90% of fetal anomaly are born to no risk mother : detection rate- 16~85%

: not obligated to perform ultrasonography in low risk or no indication

What gestational age represents the optimal time for an obstetric ultrasound examination? : 16~20 weeks : if first trimester- ovulation induction reproductive technology bleeding, hyperemesis previous ectopic preg abdominal pain, aneuploidy

How may ultrasonography be used to detect chromosomally abnormal fetuses in the second trimester in the women at high risk? : be targeted to detect fetal aneuploidy (minor anatomic features) : advanced age, multiple marker screening : no randomized controlled trial -evidence is insufficient to support or refute the general use of a specialized ultrasound examination to evaluate the entire at risk obstetric population

How is ultrasonography used to detect disturbance in fetal growth?

: intrauterine growth restriction : macrosomia

<Intrauterine growth restriction> : multitude of etiologies depending on the etiology, time of onset, severity of the growth restriction : <10th percentile (<5th or <3rd ) 10% of infants in any population not pathologically but familial & ethnic

: abdominal circumference, head circumference, biparietal diameter, femur length →caculates on the basis of formulas

: IUGR suspected→ serial measurements of fetal biometric parameters→ detailed ultrasound survey→ confirm diagnosis & severity

: amniotic fluid volume -oligohydramnios→ IURG (77~83%)

: Doppler velocimetry (umbilical arteries) -not useful as a screening useful in diagnosis & fetal evaluation

: identification of IUGR -by recording growth velocity (2~4 weeks apart)

<Macrosomia> : variability of the estimate (plus/minus 16~20%) most formulas- greater error (ex. >4,500g 12.6% , <4,500g 8.4%) : accuracy of the ultrasound estimation -sensitivity 22~44% specificity 99% positive predictive value 30~44% negative predictive value 97~99%

Conclusions Ultrasound examination : accurate method of gestational age (1st half) fetal number ,viability, placental location Diagnose major fetal anomalies Diagnosis of fetal growth abnormalities Safe for the fetus when used appropriately Specific indication are the best basis for the use of ultrasonography in pregnancy Optimal timing for single ultrasound examination : 16~20 weeks

Summary of Recommendations Serial ultrasonograms to determine the rate of growth –

every 2~4weeks Casual use of ultrasonography should be avoided Before examination, counseled the limitation of ultrasonography for diagnosis