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
