Class 12: OB 2nd & 3rd Trimester Flashcards
the gestational period in the human usually lasts ___ days, ___ weeks, ___ months
280 days, 40 weeks, 9 months
weeks of first trimester? significance of first trimester?
weeks 1-12; period of organogenesis
weeks of 2nd trimester? significance of 2nd tri?
weeks 13-26; period of organ development & differentiation
weeks of 3rd trimester? significance of 3rd tri?
weeks 27-40; fetal growth & weight gain
what is embryonic age?
embryologists consider the day of conception as the first day of pregnancy
what is another name for gestational age?
menstrual age
what is gestational/menstrual age?
the first day of LMP as the 1st day of pregnancy
gestational age is ___ weeks more than embryonic age
2 weeks
3 structures seen in 1st trimester
- gestational sac
- yolk sac
- fetal pole with FHM
when can the gestational sac be seen by?
5 weeks from LMP (TV)
when can the yolk sac be seen by?
5.5 weeks from LMP (TV)
when can the fetal pole be seen by?
6 weeks from LMP (TV)
when do the amnion & chorion merge by?
16-17 weeks
the placenta can be seen as crescent echogenic area by ___ weeks
7-8 weeks
placenta can be clearly visualized by ___ week
12th week
placenta borders can be identified by ___ week
20th week
how much does the fetal pole grow each day in 1st trimester?
1 mm/day
when is the fetus most susceptible to injury?
1st tri
amniotic fluid volume increases until ___ weeks
36-38 weeks
US appearance of amniotic fluid in 1st & 2nd tri?
anechoic
US appearance of amniotic fluid in 3rd tri?
may contain small echogenic particles (vernix)
5 functions of amniotic fluid
- cushions fetus
- allows movement
- prevents adherence of amnion to embryo
- allows symmetrical growth
- maintains constant temp
when is most of the amniotic fluid made by the mother?
prior to 20 weeks
the amount of amniotic fluid is ___ related to ___ function
directly; kidney
normal lung development depends on the exchange of ___ within the lungs
amniotic fluid
severe oligohydramnios may lead to ____ hypoplasia
pulmonary hypoplasia
oligohydramnios is idiopathic 60% of the time. T/F?
false – there is usually a cause
what are the most common causes of oligohydramnios (3)
- PROM
- IUGR/FGR
- abnormalities in fetal genituourinary tract (blockage, no renals, no renal function)
polyhydramnios is idiopathic 60% of the time. T/F?
true
when may the sonographer see amniotic membrane floating in amniotic cavity?
after 16 weeks
what can floating amniotic membranes cause?
amniotic band syndrome
what is amniotic band syndrome?
bands/tears from amnion may entangle fetal structures and cause defects
what is another name for uterine contractions?
braxton hicks contractions
what are braxton hicks contractions?
smooth contractions of the myometrium
when can braxton hicks contractions occur?
throughout pregnancy
how long do uterine contractions occur?
about 30-45 minutes
U/S appearance of contractions?
homogenous
what is cervical incompetence?
cervical dilation prior to term
what is an abnormal endocervical canal length?
< 2.5 cm
what is a cerclage?
loop placed in cervix to hold it closed
what condition is considered normal in 2nd or 3rd trimester with the maternal kidneys?
some degree of hydronephrosis
which kidney is maternal hydronephrosis more common in?
right kidney
what does EDC stand for?
estimated date of confinement (due date)
how is EDC calculated?
by the 1st day of LMP
what 4 measurements are used for dating fetus in US?
BPD, HC, AC, FL
what week do the 3 primary brain vesicles start developing? what are these vesicles called?
~ week 6
prosencephalon
mesencephalon
rhombencephalon
what cystic structure can be seen in the posterior aspect of the fetus around 6-8 weeks?
rhombencephalon
what do the lateral ventricles look like around 11-12 weeks?
butterfly appearance
the choroid plexus can be seen at the ____ of the lateral ventricles
roof
function of the choroid plexus?
makes CSF
what week can the fetal head by well appreciated by?
12th week
by what week does the appearance of each brain structure remain relatively the same?
18th week of gestation
which plane do we check the contour of the skull bones?
long axis
the 4 levels to assess when checking brain development
- most superior level with IHF
- forebrain – lateral ventricles
- midbrain – thalamus, CSP, 3rd ventricle
- hindbrain – cerebellum, 4th ventricle, nuchal fold
another name for interhemispheric fissure
falx cerebri
what is the IHF/falx cerebri?
membrane that separates the brain into 2 hemispheres
the IHF ensures the separation of the ___ occured
cerebrum
the lateral ventricles shouldn’t exceed ___ mm or ___ cm
10 mm/1cm
which part of the brain is the lateral ventricle a part of?
forebrain
where is the widest diameter of the skull?
midbrain
3 midbrain landmarks?
- CSP
- 3rd ventricles
- thalami
which direction does the apex of the thalami face?
occipital bone
where is the CSP located?
midbrain in front of the thalamus
where do you take the measurements for BPD & HC?
midbrain at the level of the thalamus, CSP & 3rd ventricle
landmarks of the hindbrain?
cerebellum, 4th ventricle, nuchal fold
the cerebellum is at the back of the cerebral ___ within the ___ fossa
peduncles; posterior
what connects the cerebellar hemispheres?
vermis
what is the space in the posterior fossa that is filled with CSF?
cisterna magna
a normal cisterna magna may exclude almost all spinal defects. T/F?
true
what is the normal measurement of the cisterna magna?
cisterna magna shouldn’t exceed 10 mm/1 cm
what is the nuchal fold?
skin fold
U/S appearance of occipital bone?
echogenic
where are the orbits seen seen in comparison to the cerebellar plane?
inferior to cerebellar plane
5 routine measurements for dating the fetus?
- BPD
- HC
- AC
- FL
- AFI
6 nonroutine measurements for dating the fetus?
- lateral ventricles
- cisterna magna
- cerebellum
- orbits
- nuchal fold
- nuchal translucency
what does the BPD assess?
gestational age
what weeks is the BPD most accurate?
weeks 14-20
How to place calipers for the measurements for BPD?
outer to inner
landmarks for the BPD?
midbrain: thalamus, CSP, 3rd ventricle
what does the HC assess?
gestational age
is the HC or BPD more accurate? why?
HC bc it isn’t affected by head shape
where do you take the measurements for HC?
outer to outer with ellipse or caliper button
what are the 2 variations in head shape?
- brachycephaly
- dolichocephaly
what is brachycephaly?
a more rounded head shape
what is dolichocephaly?
more elongated head shape
why was the cephalic index (CI) created?
it helps determine a normal fetal head size regardless of variations in fetal head shape
formula for CI?
CI = BPD/OFD x 100
what is a normal cephalic index range?
75-85%
what is considered brachycephaly in regards to the CI?
over 85-90%
what is considered dolichocephaly in regards to the CI?
< 70%
the cerebellum measurement can be used up to ___ weeks of gestation
24 weeks
the cerebellum measurement correlates with fetal ___ from ____ weeks of gestational age
fetal age from 16-24 weeks
for the cerebellum measurement, the imaging plane is ___ & ___ to the BPD level
parallel & inferior
U/S appearance of cerebellar hemispheres?
2 hypoechoic hemispheres
U/S appearance of vermis?
hyperechoic
the ___brain is anterior to vermis
midbrain
normal measurement of nuchal fold at the level of the cerebellum shouldn’t exceed ___
6 mm
a nuchal fold measuring 6 mm or more may indicate ___
down’s syndrome
the lateral ventricles can be clearly identified by which week of gestation?
16th week
how do you measure the OFD?
from midpoint of frontal to midpoint of occipital
how do you measure the cisterna magna?
from outer of vermis to the inner of occipital bone (ONLY CM)
both the NT & nuchal fold rule out ___ abnormalities
chromosomal
which trimester is the NT measured in?
1st trimester
which plane is NT measured?
sagittal/long axis
if the NT is equal to or greater than ___, it can indicate ___ abnromality
3 mm; chromosomal abnormalities
which trimester is the nuchal fold measured in?
2nd tri
what plane is the nuchal fold measured in?
transverse or cross-section
the nuchal fold is measured at the level of the ____
cerebellum
how do you measure the nuchal fold?
from outer occipital bone to the outer skin
normal measurement for nuchal fold?
less than 6 mm
if the nuchal fold measures 6mm or greater, this can indicate what 4 conditions?
- chromosomal abnl
- fetal demise
- skeletal dysplasia
- fetal hydrops
2 measurements for the orbits
- OOD/binocular distance
- IOD/interocular distance
what does the OOD measure?
gestational age
when do you measure OOD?
when unable to get BPD or HC
what does IOD rule out?
hyper/hypotelorism
best plane to image cleft lip?
sagittal
most common fetal neck mass?
cystic hygroma
the vertebrae can be well visualized by ___ weeks of gestation
16
what is the preferred plane to image the spine? SAG or COR?
SAG
how does the spine look on U/S in TRV?
3 highly echogenic ossification centers
U/S appearance of the fetal spine in SAG?
railroad sign – 2 curvilinear lines extending from cervical spine to sacrum
U/S appearance of fetal spine in COR?
3 parallel lines that can be imaged from cervical spine to lumbar sacral region
define fetal presentation
the fetal part closest to the cervix
3 types of fetal presentation
- cephalic
- breech
- other
define fetal lie
the long axis orientation of the fetus
3 types of fetal lie
- longitudinal
- transverse
- oblique
U/S appearance of fetal lungs?
solid masses between fetal heart and ribs
U/S appearance of fetal lungs in early fetal life compared to liver?
lungs are iso/hypoechoic to liver
U/S appearance of fetal lungs later in fetal life compared to liver
hyperechoic to liver
lung maturity is determined by ____
amniocentesis
what ratio is checked with amniocentesis to determine lung maturity?
lecithin-sphingomyelin ratio
an LS ratio of ___ indicates mature lungs
2+
what is the fetal heart rate after the 1st tri?
120-160 BPM
what is the most important view for the fetal heart?
4 chamber view
what percentage of all abnormalities can be ruled out with the 4th chamber view?
65%
the fetal diaphragm can be seen in ___ of fetuses by ___ weeks
1/2 of fetuses by 20 weeks
the fetal kidneys are seen by ___ weeks
15-16 weeks
the fetal stomach should be documented by ___ weeks
20 weeks
U/S appearance of fetal kidneys in early vs later gestation
kidneys are hypoechoic in early gestation & look similar to adult kidneys in later gestation
which measurement does fetal weight rely on the most?
AC
what is the standard measurement for dating the fetus after 12-15 weeks?
AC
landmarks for AC?
stomach
ossification centers of spine
portal sinus
how to measure AC?
outer to outer using ellipse
how many vessels are in the umbilical cord?
3 – 1 umbilical vein & 2 spiral arteries
which vessel brings oxygen & nutrient rich blood to the fetus?
umbilical vein
what do the umbilical arteries do?
carry nutrient poor & O2 poor blood away from fetus to the placenta
which trimester is the fetal bowel seen?
3rd tri
the fetal urinary bladder can be seen by ___ weeks
20 weeks
seeing the UB ensures the ____ of at least ___
presence; 1 kidney
how to measure femur length?
measure only diaphysis of bone
when is femur length more accurate in dating?
late pregnancy
fetal genitalia can be best identified after ___ weeks
20
