role of ultrasound in obstetrics Flashcards
when is it best to perform an ultrasound to detect trisomies ?
from 10-13 weeks
when is it best to perform an ultrasound to detect ectopic pregnancies?
from 5-8 weeks
when is a 1st trimesteric ultrasound performed ?
10-13 weeks
how can we make an accurate evaluation of gestational age ?
using the crown-rump length
what are the indications associated with the bladder when it comes to early pregnancy ultrasound vs early pregnancy trans-vaginal ultrasound ?
early preg abdominal US - full bladder
early preg trans-vaginal US - empty bladder
when checking for an ectopic pregnancy what type of ultrasound is used ?
trans-vaginal ultrasound from week 5-8
in which disease is trans-vaginal ultrasound a gold standard ?
placenta praevia
what is the earliest sign of pregnancy that can be found on ultrasonography ?
gestational sac
how early can a gestational sac be seen on ultrasound ?
from 4 to 5 weeks
how does a gestational sac differ from a pseudogestational sac ?
gestational sac - has a double ring sign/ double decidual sign
and is intradecidual ( embedded into the endometrium rather than appearing centrally as a pseudogestational sac would)
what should you expect after the appearance of a gestational sac ?
appearance of a yolk sac followed by fetal pole followed by cardiac activity
when do you expect to see a yolk sac ?
from 5 to 6 weeks or with a b-hcg level of 7000m IU/ml
what mainly differentiates a pseudogestational sac from a pseudo sac ?
the yolk sac
when do we expect to see a developing embryo ?
at 6-7 weeks
at what CRL length is a heart beat or a pulse seen ?
at 5mm vaginally
what is the most common cause of embryonic death ?
chromosomal abnormality
when do we consider a pregnancy non-viable on trans-vaginal ultrasound
if there is no fetal heart rate whilst having a CRTL of more than 7
or
if there is no fetal pole where the MSD is more than 25 mm with no embryo
by how much are the fetus and gestational sac expected to grow per day ?
1 mm
what is the discriminatory zone of b-hcg ?
relies on BHCG increasing by more than 66% in 48 hours if not and there is no bleeding and the uterus is empty
consider ectopic pregnancy
what is a blighted ovum ?
a blighted ovum or an anembryonic sac is intra decidual but has reached a diameter of 25 or more with no yolk or fetal pole
what is the best thing to do if you are not sure if the sac is anembryonic or not ?
repeat in a week
what does a molar pregnancy look like on ultrasound ?
snow storm appearance
what is commonly found in the ovaries in association with molar pregnancies ?
theca lutein cysts , secondary to BHCG
which type of ultrasound is used to detect a gestational sac ?
trans-vaginal ultrasound
before the formation of the placenta how does exchange between the embryo and the mother happen ?
through the yolk sac
what is the natural course of the yolk sac ?
yolk sac disappears and is sonographically undetectable by week 14
what is the earliest sign of a polyamniotic pregnancy ?
multiple yolk sacs
when is the CRL measurement made ?
between 7 to 13 weeks
what are the second trimesteric biometric measurements ?
bi-parietal occipito-frontal diameter head circumference abdominal circumference femur length
how can we monitor growth of long bones ?
femur length
which part of the femur is used for measurement of the femur length ?
entire diaphysis without the epiphysis
what is the most important function of measuring FL?
excluding dwarfism
what is the most important measurement to take in late pregnancy ?
abdominal circumference
when is the fetal biophysical profile assessed ?
third trimester
how can fetal death be confirmed ?
absence of cardiac activity for at least 2 to 3 minutes , which should ideally be confirmed by 2 or more examiners
what is the most ideal time to determine fetal sex ?
17-20 weeks
what are the components of biophysical profile ?
fetal breathing movement fetal tone fetal movement amniotic fluid volume non-stress test
what is the modified BPP ?
combines the non stress test with amniotic fluid assessment
what three blood vessels are assessed using doppler ?
umbilical artery
middle cerebral artery
ductus venosus
which of the three arteries can be used to decide the timing of delivery ?
ductus venosus
how is liquor assessed ?
measure the dimensions of the largest vertical pocket of amniotic fluid
which measure is the most accurate measure of amniotic fluid ?
amniotic fluid index
how is the amniotic fluid index measured ?
uterus is divided into four quadrants and sum of all four measurements are taken
