Outcome 2: Fetal Lie, Growth, & Wellbeing

initial survey

• when beginning a 2nd/2rd trimester OB exam, in both SAG and TRV planes we look for..

  • # of fetuses

  • FHR

  • fetal lie and presentation

  • any obvious, large abnormalities

fetal lie, presentation, and situs

fetal lie:

• the relationship b/w fetus and the pt/maternal body

fetal presentation:

• reference to the part of the fetus that’s overlying the internal cervical os

• can further describe fetal lie (ie. frank breech, complete breech, etc.)

• often used interchangeably w/ fetal lie

fetal situs:

• position and orientation of the heart, stomach, liver, spleen, aorta, and IVC relative to midline fetus

• we observe heart and stomach on LEFT side of chest and abdo

uterine growth during pregnancy

• maternal uterus expands upwards and outwards to accommodate the fetus, placenta, and amniotic fluid

symphysis-fundal height (SFH):

• distance b/w symphysis pubis and uterine fundus; measured in dr’s office

• size correlated to GA (ie. 24cm SFH = 24 wk GA)

weights of uterus:

• before preg. = ~50-70g

• 12wk = ~140g

• 20 wk = ~300g

• 36wk = ~1000g

fetal lie types

longitudinal:

• fetus parallel w maternal body

  • cephalic = head down

  • breech = head up

transverse:

• fetus perpendicular w/ maternal body

oblique:

• fetus diagonal w/ maternal body

mobile/variable:

• fetal lie changes throughout exam

—

• you MUST check fetal lie first to know what side of baby is their left side before confirming that their heart and stomach are on the correct side of their body

breech lie types

frank breech:

• fetal bum presenting

• legs and knees are extended

• feet by fetal head

complete breech:

• fetal bum presenting

• legs and knees are flexed

• feet by fetal bum

footling/incomplete breech:

• fetal feet presenting

• either 1 foot (single footling) or both feet (double footling) closest to internal cervical os

fetal lie: transverse

• we need to also comment on where fetal head is in relation to mom

fetal heart and abdomen - fetal situs

• if we look closely, we can actually see which chambers are atria and which ones are ventricles

• the atria are further back in the chest, more round, and thinner walls

• the ventricles are more anterior in the chest, pointed, with thicker walls

the ventricles point towards the left side of the chest, so the half of the chest with the majority of chambers of the heart is the left side.

terminology

appropriate-for-gestation age (AGA):

• a fetus whose size is within the normal range for its GA (bw 10%-90%ile)

large-for-gestational age (LGA):

• a fetus whose size is above a predefined threshold for its GA (>90%ile)

small-for-gestational age (SGA):

• a getus whose size is below a predefined threshold for its GA (<10%ile)

• normal but smaller than avg.

fetal growth restriction (FGR) or intrauterine growth restriction (IUGR):

• a fetus that hasn’t achieved its growth potential

• abnormally restructed in growth

macrosomia:

• a baby who measures >4000g at birth

fetal growth and biometry

biometry:

• measurements of fetal body structures in an attempt to establish the GA and ensure appropriate interval growth

—

• the accurate estimation of GA underlies all OB management decisions

1st trimester biometry:

• crown-rump-length (CRL)

• 1^st trimester estimated gestational age = X ± 1 week

• we can’t use CRL when it’s >84mm (~14wks) bcuz that’s the machine’s limit

2nd and 3rd trimester biometry

biparietal diameter (BPD):

• linear measurement of the TRV diameter of fetal skull through transthalamic plane

• leading edge of the near field to leading edge of far field

head circumference (HC):

• ovoid measurement along the outer perimeter of the fetal skull in transthalamic plane

• doesn’t include skin

abdominal circumference (AC);

• ovoid measurement along the outer perimeter of the fetal abdominal soft tissue in a TRUE TRV plane at the lvl of the stomach and umb. vein

• includes skin

femur length (FL):

• linear measurement of the axial length of the ossified portions of the femur

—

• gives us an estimated GA and fetal weight

thalamic view for BPD and HC

view for biparietal diameter and head circumference:

• TRV image of fetal head at lcl of paired thalami and cavum septi pellucidi (CSP), w/ symmetry of the thalami and cerebral hemispheres and w/o visualization of the posterior fossa

sonographic landmarks:

• paired thalami = paired ovoid structures in middle of brain (* in above image)

• cabum septi pellucidi (CSP) = fluid-filled space anterior to thalamus (anechoic space b/w arrows in above image)

• falx = linear structure separating cerebral hemispoheres (left side arrow in image)

• ovoid fetal head w/ symmetrical hemispheres

abdominal circumference (AC)

view:

• stomach and curved, intrahepatic portion of portal vein must be seen

• fetal kidneys NOT seen

• round abdomen w/ ribs symmetric on either side of abdomen

• true TRV plane

femur length (FL)

• image one of the femur bones in LAX, horizontal on screen

• measure blunt ends of echogenic femur bone (diaphysis), don’t include pointed ends or epiphysis

—

• as the pregnancy continues, the epihysis locations on either end of the femur bone will be more clearly seen

  • hypoechoic on u/s

occipitofrontal diameter (OFD) - optional measurements

• linear measurement of the length diameter of the fetal skull through transthalamic plane

• measured from mid bone of anterior skull to mid bone of the posterior skull

• perpendicular to BPD

• contributes to cephalic index (CI)measurement, not routinely measured

cephalic index (CI) - optional measurements

• a ratio calculated using BPD and OFD

• used to indicate fetal head shape

CI = BPD/OFD x 100

—

• mesocephalic (normal) = 70-85%

• brachycephalic (abnormally wide) = >85%

• dolichocephalic (abnormally long) <70%

—

• not routinely measured

humerus length (HL) - optional measurements

• linear measurement of axial length of the ossified portions of the humerus

• same method as FL, measured in LAX and the blunt ends of the bone

• not routinely measured

orbital measurements (OOD, IOD, OD) - optional measurements

orbital measurements:

• linear measurements of fetal orbits (eye sockets) acquired in TRV view of fetal head at lvl of orbits

—

outer orbital distance (OOD):

• aka binocular distance (BOD)

• linear measurement from outer edge of one orbit to outer edge of other orbit

inner orbital distance (IOD):

• aka interocular/interorbital distance

• linear measurement of the distance b/w inner edges of both orbits

orbital diameter:

• linear measurement of the diameter of one orbit

—

• normally

  • IOD = OD

  • OOD = IOD x 3 = OD x 3

fetal size vs. fetal growth

fetal size:

• indicated the estimated fetal weight and corresponding estimated GA at any given point in time

fetal growth:

• indicated the estimated fetal weights and corresponding estimated GA compared over diff. points in time

• fetal growth = fetal size + time

fetal growth charts

canadian standard:

• fetal growth chart are created from research studied that collect fetal biometric measurements from large populations of pregnancies

• a percentile curve is generated, showing the expected distribution of measurements at each GA

• most u/s departments in North America use the Hadlock charts, but there isn’t necessarily a single Canadian fetal growth chart every Canadian u/s department uses

controversy:

• whether the estimated weight of a fetus should be compared w/ norms from the overall population (ie. Canadian pop.) or to customized norms (ie. ethnicity)

—

• BPD, HC, AC, FL, and EFW growth charts are embedded into the u/s machines

• growth chart trajectory includes the median (avg, 50%) and extremes

fetal growth charts cont.

weight gain:

• weight gain = diff. b/w two estimated weights (of 2 diff. u/s exams)

EXAMPLE:

Patient A arrives for an ultrasound exam at 28w0d. After the ultrasound is complete, biometry measurements gave us an EFW of 1005 grams. Based on growth chart (seen above), this fetus measures exactly 50%ile.

Patient A arrives for another ultrasound exam exactly 4 weeks later, at 32w0d. After the ultrasound is complete, biometry measurements gave us an EFW of 2000 grams. Based on growth chart, this fetus measures nearly 90%ile.

Weight Gain = Difference in two weights = 2000g – 1005g = 995 grams of weight increase in 4 weeks time.

—

• biometry measurements and estimated fetal weight should only be assessed after 2 wks has passed since previous measurements were acquired

large-for-gestational age (LGA)/macrosomia

LGA:

• >90%ile of estimated fetal weight

macrosomia:

• >4000g birthweight

—

risk factors:

• maternal obesity

• hx of previous LGA infant

• prolonged pregnancy (>40wk GA)

• excess pregnancy weight gain

• multiparity

• advanced maternal age

complications:

• inc. morbidity/mortality

• shoulder dystocia

• fractures

• facial/brachial plexus palsies

• traumatic delivery

• asphyxia

• meconium aspiration

• neonatal hypoglycemia

sono signs:

• EFW >90%ile for GA

• usually affects abdomen circumference (AC) in 3rd tri

• potential for macrosomia

diabetic patients

• diabetes mellitus is a chronic condition where the body can’t properly use blood sugar (glucose) » leading to high blood sugar lvls

• inc. lvls of maternal insulin leads to overgrowth of fetal abdomen, but normal head

• ~28-32 weeks GA, fetuses will have larger than normal AC measurement » often causing LGA/macrosomia

complications:

• inc. morbidity/mortality

• shoulder dystocia

• fractures

• facial/brachial plexus palsies

• traumatic delivery

• asphyxia

• meconium aspiration

• neonatal hypoglycemia

small-for-gestational age (SGA)/fetal growth restriction (FGR/IUGR)

SGA:

• <10%ile of EFW

FGR/IUGR:

• a fetus is one that hasn’t achieved its growth potential

• abnormally restricted growth

—

risk factors:

• small parents

• placental abnormalities

• chromosomal abnormalities/aneuploidy

• congenital malformations

• infections

• maternal abnormalities

• multiples

complications:

• inc. morbidity/mortality

• respiratory distress syndrome

• acidosis

• NICU admission

sono signs:

• EFW <10%ile for GA

• constitutionally small; may also notice small pt/parents

sono signs of FGR (bottom images):

• delayed/absent growth on serial u/s exams

• abnormal umb. artery doppler

• oligohydramnios

• grade 3 placenta

• low BPP score

fetal wellbeing

• healthy status of a fetus

• ability to detect signs of fetal distress early helps supports maternal and fetal health & allows time to prepare for safe delivery and identifies potential interventions that may be considered

indications:

• FGR

• oligohydramnios

• multiples

• dec. fetal movement

• prior stillbirth

• maternal HTN

• diabetes

• renal disease

assessments:

• ultrasound assessments..

  • biophysical profile

  • dynamic structures

  • fetal doppler

• other..

  • non-stress test (NST)

  • cardiotocography (CTG)

  • contraction stress test (CST)

biophysical profile

• assessment of fetal wellbeing, scored out of 8

• commonly performed after 28wks in 3rd tri.

• fetus has 30 mins to demonstrate each parameter to receive all points

parameters used (each /2 = /8):

1. fetal movement

2. fetal tone

3. fetal respiration

4. amniotic fluid

additional parameter (making score /10):

1. non-stress test (NST)

—

clinical indications:

• diabetes

• HTN

• renal disease

• asthma

• multiples

• current concerns

• past pregnancies w/ concerns

• past due date (>41 wks GA)

primarily tests for:

• asphyxia

• low cord pH

• cerebral palsy

• stillbirth

fetal movement - biophysical profile

• 3 or more discrete gross body/limb movements within 30 mins

  • “movement” indicated overall body or limb activity

sonographically:

• movement such as kicking, rolling, stretching of body

• usually seen in fetal limbs

fetal tone - biophysical profile

• one or more episodes of active extension and flexion of a fetal extremity OR opening/closing of hand within 30 mins

• “tone” indicated specifically muscle tone

  • ie. actively extending a limb or trunk, and then returning it to a flexed position

sonographically:

• extension and flexion of fetal spine

• extension and flexion of limbs

• opening and closing of hand

fetal respiration - biophysical profile

• one or more episodes of fetal breathing lasting at least 30 secs, within 30 mins

• hiccups are considered breathing activity

sonographically:

• alternating squeezing of chest (ribs) and abdo wall, in inhale/exhale like motions

• diaphragm and abdominal contents moving up and down in chest/abdomen

• hiccups are shorter, quicker versions of these movemtns

• best seen in coronal view of fetal chest/abdo

amniotic fluid - biophysical profile

• AFV = single pocket of amniotic fluid at least 1cm x2cm in AP dimension

• SDP = normal is >2×2cm

sonographically:

• can’t measure through fetal tissue of amniotic cord

• pockets of fluid are typically smaller in 3rd tri

non-stress test (NST)

• measurement of fetal movement, heart rate, and uterine contractions for fetal wellbeing

• inc. fetal HR w movement indicated appropriate O2 lvls in fetus

• completed at dr’s office w/ cardiotocograph machine

results:

1. reactive (normal) = fetal HR goes up 2 or more times in testing period (2 points)

2. nonreactive (abnormal) = no change in FHR when baby moves (no points)

cardiotocography (CTG)

• measurement of fetal movement, FHR, and uterine contractions during labour

• uses cardiotocograph machine to look for signs of fetal distress

contraction stress test (CST)

• hormone (oxytocin) is administered to pt. to stimulate stress of baby by creating uterine contractions

• observing the change in FHR befire and after contraction can indicate fetal wellbeing or distress

• normally, HR should lower then return to normal after contraction

• CST may be performed to further test for signs of fetal distress after an abnormal BPP or NST

• abnormal CST may suggest C-section over vaginal birth

• >34wks GA (late 3rd tri)

dynamic structures

• aka “things that change”

• fluid-filled structures in fetus and fetal environment that are routinely assessed at every OB u/s

• another way fetal wellbeing can be assessed is observing these structures

includes:

• lateral cerebral ventricles

• cavum septi pellucidi (CSP)

• cisterna magna

• 4C heart

• stomach

• kidneys

• bladder

• amniotic fluid

fetal hypoxia and asphyxia

hypoxia:

• when the fetus is deprived of an adequate supply of O2

• one of the leading causes of fetal mortality

asphyxia:

• severe form of O2 deprivation (worse form of fetal hypoxia)

• one of the leading causes of fetal mortality

—

causes:

• FGR (can also be a consequence)

• umb. cord prolapse

• cord occlusion/thrombosis

• placental insufficiency/infarction

• maternal smoking

—

• fetal doppler is used to assess for risk of FGR bcuz waveform appearance, measurements, S/D ratio, RI, and PI can indicate hypoxic changes

fetal doppler

• PW and colour

• helpful in evaluating fetal wellbeing and fetal risk of FGR

vessels that can be evaluated:

• umb. artery/arteries

• umb. vein

• ductus venosus

• middle cerebral artery (MCA)

• maternal uterine artery

fetal doppler rules:

• careful technique and proper machine settings must be used

• adhere to ALARA principle

• only used in high-risk fetsuses

umbilical artery (UA) doppler

• typically performed >24wks GA

• normal = low resistance

• abnormal = high resistance waveform, absent or reversed flow

• normal S/D ratio..

  • 24wks = 3.23

  • 40 wks = 2.19

umbilical vein doppler

• continuous, monophasic flow towards fetus

• normal mean velo. = 10-15cm/s

• abnormal = pulsatile flow

ductus venosus doppler

• connects umbilical vein to the IVC » becomes ligamentum venosum

• venous structure

• triphasic, antegrade, continuous flow towards fetal heart

• abnormal = absent or reversed flow

middle cerebral artery (MCA) doppler

• MCA is near circle of willis

• helps assess for FGR, fetal hypoxia, and fetal anemia (fetal distress)

• imaged in TRV view of fetal brain @ lvl of cerebellum

• not commonly performed

• normal = high resistance waveform

• abnormal = low resistance waveform

sonography:

• obtain TRV view fetal head at lvl of thalami/cerebellum

• place colour to identify rt and lt MCAs

• perform PW doppler on bilateral vessels 3x

middle cerebral artery (MCA) doppler chart

• normal values change over time

• peak values occur ~28-30wks GA

maternal uterine artery doppler

• lateral sides of cervix/lower uterine segment contains uterine arteries

• normal = low resistance waveform w RI <0.55

• abnormal = inc. PI, diastolic notch, and RI >0.55

• abnormal waveforms indicate abnormal vasculature of the placenta or placental insufficiency

sonography:

• pt. has full bladder

• SAG cervix, sweep laterally and angle slightly

• uterine arteries found on lateral sides of cervix, crossing paths w external iliacs

• assess and image bilateral uterine arteries 3x

maternal uterine artery doppler chart

• normal values change over time

• values steadily dec. throughout pregnancy

brain sparing effect

• redistribution of oxygenated blood to vital fetal organs (brain, heart, adrenals) when a fetus is in distress (placental insufficiency, hypoxia, growth restriction)

• MCA doppler waveform changes from the normal high-resistance wave to an abnormal low-resistance wave » helping get as much oxygenated blood to the brain as possible, inc. fetal survival

• brain sparing = blood shunted during fetal distress = low resistance MCA waveform

• seen as vasodilation in the brain on OB u/s

cerebroplacental ratio (CPR)

• ratio of resistance index (RI) or pulsatility index (PI) of middle cerebral artery (MCA) compared to umb. artery

CPA = (MCA RI/PI)/(UA RI/PI)

• normal = CPR >1.0

• abnormal = CPR <1.0