radiology in OB Flashcards
safety of x-rays depends on what?
“all-or-none” phenomenon
location of irradiation
amt of radiation
timing (during pregnancy) of exposure
harmful effects of ionizing radiation
cell death & teratogenicity
carcinogenesis
genetic effects or mutations in germ cells
high dose radiation 5.5-6 days after ovulation, before implantation
spontaneous abortion
high dose radiation (>200 rad) effects after implantation
growth restriction
microcephaly
mental retardation
when does high dose radiation have the greatest effect
8-15 weeks
no proven effect of high dose radiation when
25 wks
risk of severe mental retardation occurs at what level of rads?
40% at 100 rad
60% at 150 rad
with doses < 5 rads, no increase in
fetal growth restriction
fetal anomalies
spontaneous abortion
-threshold may exist at 20-40 rad
genetic effects of radiation
may increase frequency of natural mutations, NOT create de novo mutations
no increased risk of genetic d/o’s has been noted in any human pop at any dose
MRI & pregnancy
magnets alter E state of H+
may be helpful in Dx of fetal CNS defects, IUGR, placenta accreta
some people advise against use in 1st trimester
nuclear medicine & pregnancy
“tagging” a chemical agent w/ radioisotope-fetal exposure depends on radioisotope’s physical & biochemical properties
Tc 99m nuclear medicine
used in brain, bone, renal, CV scans
exposure < 0.5 rads
VQ scans Tc 99m for
perfusion
VQ scan 127Xe or 133Xe for
ventilation
exposure ~ mrads (o.05 rads)
ULS in pregnancy
sound waves, not ionizing radiation
no reports of adverse fetal effects
FDA arbitratily limits E exposure to 94mW/cm2
no CI in pregnancy
indications for 1st trimester ULS
confirming fetal viability "dating" the pregnancy by crown-rump length ruling out extrauterine pregnancy diagnosing multifetal pregnancy guidance for removal of IUD r/o molar pregnancy guidance for chorionic villous sampling nuchal translucency testing
pregnancy dating
accuracy of ULS varies by trimester error of ULS -1st trimester: 4 day- 1 wk -2nd trimester: 10 days- 2 wks -3rd trimester: 2-3 wks assessment of fetal growth patterns linked to ULS error
ectopic pregnancy & ULS
most ectopics are tubal presentation: 7-8 wks triad: pain, bleeding, +UPT ULS cannot definitively r/o ectopic, but can rule in intrauterine pregnancy less common sites: cornual, cervical
pregnancy w/ IUD
miscarriage risk is 10% greater w/ IUD in situ
string may retract into cervix as uterus enlarges
molar pregnancy & ULS
molar gestation-neoplactic placental growth
fetus present (partial) or absent (complete)
inheritance: uniparental disomy
Lab: high levels of hCG
Sx’s: hyperemesis, hyperthyroidism
ULS: “snowstorm” or “grape-like” clusters
high incidence of fetal CNS anomalies
CVS & ULS
bx of placental tissue at 10-13 wks
Dx’s chromosomal or genetic d/o’s for which DNA testing is available
ULS guides needle/catheter into placental tissue
fetal nuchal translucency- edema in the fetal neck
11.5 & 14.5 wks
abnormal edema assoc. w/ chromosomal & fetal structural abnormalities
-down syndrome (T21) detection rate: 80% w/ NT alone, 90% w/ assoc. biochemical markers
Assessment by absolute size (>3.5 mm) for structural defects. Gest age dependent nmls (2.2-2.8 mm) for chromosomal abnormalities
2nd trimester ULS uses
assessing gestational age multifetal pregnancy detection screening for fetal anomalies placental localization & eval amniotic fluid eval guidance for amniocentesis
components of a 2nd trimester ULS
gestational age/ fetal growth fetal position fetal # placental location amniotic fluid vol. uterine eval- fibroids, anomalies cervical evaluation fetal anatomy
placenta on ULS
where is it? -anterior -posterior -fundal -covering the cervical os is it normal? -molar pregnancy -separated? abruptio placenta
placenta previa
complete, partial or marginal
common in 2nd, rare in 3rd trimester
higher incidence in multipares, elderely, previous c-section or abortion
may detect retroplacental or retromembranous clot- abruptio placenta
amniotic fluid assessment
increased= polyhydramnios
- DM
- upper GIT obstruction
- chromosomal abnormalities
- muscular lesions affecting swallowing
decreased: oligohydramnios - rupture of the membranes
- absent fetal renal tissue/ lower UT obstruction
- intrautering growth restriction
uterine eval w/ OB sonography
overall shape & size presence of anomalies -uterus didelphys (including double cervix) -uterine septa, bicornuate uterus presence of tumor-leiomyoma
cervical eval during 2nd trimester
nml cervical length: >2.5 cm
borderline area: 2.0-2.5 cm
abnormally short: membranes
placement of cervical cerclage
fetal anatomic survey: “the level II ULS”
systemic survey for fetal anomalies
performed usually bet. 16-22 wks
“the level II ULS” survey- what it looks at
CNS cardiopulmonary GI GU MS umbilical cord fetal exterior
CNS & spine
cerebral ventricles
posterior fossa & cerebellum
cavum septum pellucidum
cranium- encephalocele, hypo & hypertelorism
spina bifida- myelocele, myelomeningocele
cardiopulmonary assessment
4 chamber hear, outflow tracts
echogenic foci
cardiac masses-myoxoma, rhabdomyoma
pulmonary evaluation-diaphragmatic herniation
-masses: cystic adenomatoid malformations (CCAM), bronchopulmonary sequestration
-effusions
GI assessment
GI tract obstruction
-absence of ST “bubble”- tracheo-esophageal fistula
-“double bubble”- duodenal atresia
-anal atresia
Ascites
Echogenic bowel-brightness=bone brightness
-T21, CF, intrauterine bleeding, infxns (CMV, toxoplasmosis)
GU assessment
nml anatomy- kidneys & bladder seen, ureters & urethra not seen
Abnormal: dilated renal pelvis-obstructive, “flaccid”
obstructions: UPJ, UVJ, urethral (bladder outlet), hydronephrosis
renal, ovarian cysts
hypospadias, penile anomalies
cystic renal changes
umbilical cord assessment
# of vessels- 2 vessel cord associated w/ chromosomal, skeletal, GU tract abnormalities insertion site into abdomen- defects gastroschisis, omphalocele
MS assessment
calvarium
long bones- presence/absence, length, bowing, fractures
digits- # & orientation
abnormalities: skeletal dysplasias, spondylolystheses, ichythyoses
fetal exterior/integument assessment
craniofacial- cleft lip & palate, cystic hygroma
teratomas- sacrococcygeal
3rd trimester assessment
fetal growth- biometry, fluid assessment: AFI
fetal well-being- biophysical profile, doppler studies
fetal pulmonary maturity studies-LBC, SA ratio, LS ratio, PG level
Macrosomia: > 90th % for GA
often assoc. w/ DM
CPD/ shoulder dystocia
US widely used to est. fetal wt
C-section recommended for 4750 gm (non-diabetic), 4250 gm (diabetic)
IUGR < 10th % for GA
chromosomal abnormalities renal dz & HTN connective tissue dz- SLE perinatal infxns- CMV, toxoplasmosis, etc thrombophilia- clotting abnormalities placental abnormalities
fluid assessment
amniotic fluid vol. is an indicator of fetal renal output
decreased amniotic fluid is assoc. w/ increased rate of perinatal mortality
biophysical profile
excellent predictor of fetal well being 4 ULS parameters +NST -fetal breathing -fetal tone -fetal mvnt -amniotic fluid vol. (2 cm pocket) 2 pts for each nml parameter nml:>/= 7 points
