Fetal Growth Assessment

OB I

Preterm

born prior to 37 menstrual weeks

Early term

born between 37-39 menstrual weeks

Full term

born between 39-41 weeks

Later term

born between 41-42 weeks

Post term

born later than 42 weeks

IUGR

intrauterine growth restriction

described as a fetal weight at or below 10% for a given gestational age

complicates 3-7% of all pregnancies

Babies with IUGR are at a greater risk of

antepartum death

perinatal asphyxia

neonatal morbidity

later developmental problems

Most significant maternal factors for IUGR

history of a previous fetus with IUGR

significant maternal hypertension and/or smoking

presence of a uterine anomaly (bicornuate, large fibroid, significant placental hemorrhage)

Placental insufficiency with maternal smoking

smoking decreases circulation → circulation slows to the placenta → baby doesn’t get enough blood via the placenta

Most effective way to see IUGR

abdominal circumference because it is the MOST sensitive

Symmetric IUGR

20-30% of all IUGR cases

usually the result of a first trimester insult

TIMING OF THE INSULT IS MORE IMPORTANT THAN THE INSULT ITSELF

Symmetric IUGR first trimester insults

chromosomal abnormality

intrauterine infection

severe maternal malnutrition

fetal alcohol syndrome

severe congenital abnormality

uncontrolled diabetes

genetic defects

Symmetric IUGR is characterized by a fetus that is small in these physical parameters

BPD

HC

AC

FL

Asymmetric IUGR

begins late in the second or third trimester resulting from placental insufficiency

Signs of asymmetric IUGR

fetus shows head sparing at the expense of abdominal and soft tissue growth

femur length exhibits varying degrees of compromise

MOST COMMON form of IUGR

asymmetric

usually related to placental issues (insufficiency, abruption, infarction, neoplasm)

Maternal disease that may cause placental insufficiency

diabetes

chronic hypertension

cardiac or renal disease

abruption placental

multiple pregnancies

smoking

poor weight gain

drug usage

uterine anomaly

anemia

maternal age

Grade 3 placenta before 36 weeks and a decreased thickness indicates:

asymmetric IUGR

Asymmetric IUGR is characterized by

an appropriate BPD and HC (head sparing)

disproportionate AC

femur length may or may not be affected

Head sparing theory

fetal blood is shunted away from other vital organs to nourish the brain and heart

Which fetal organ is more severely affected in IUGR

the liver

HC/AC ratio

normal pregnancy: ratio decreases

asymmetric IUGR: loss of subcutaneous tissue and fat, ration increases

EFW

MOST reliable estimation of fetal weight that incorporates all fetal diameters

Hadlock EFW

uses HC, AC, and FL to predict IUGR

HC gives a better prediction than BPD

Symmetric IUGR ______ be diagnosed in a single examination

cannot

Biophysical profile (BPP)

cardiac stress test (NST)

fetal breathing movement (FBM)

gross body movement (FM)

fetal tone (FT)

amniotic fluid volume (AFV)

BPP rules

time limit is 30 minutes

each variable is assigned a 2 or a 0

an 8 - 10 or 6 - 8 is normal (4-8 is abnormal)

score of 0 to 2 indicates either immediate delivery or extending the test time

not done until after 28 weeks

Fetal breathing movements

2 points awarded if one episode of breathing lasts 30 seconds

described as the inward movement of the chest wall with outward movement of the anterior abdominal wall during inspiration

Fetal body movements

at least 3 definite extremity or trunk movements must be observed within the 30 minute time frame to score a 2

needs to be unprovoked

Fetal tone

presence of at least one episode of extension and immediate return to flexion of an extremity or the spine

ex. open and close the hand

unprovoked

The goal of the BPP

find a way to predict and manage the fetus with hypoxia

Amniotic fluid volume/index (AFV) (AFI)

evaluation of the four quadrant amniotic fluid volume is considered normal if the fluid measures at least 2 cm or more in 2 planes

all quadrants should be between 8-22 cm

remember to put color on to make sure the umbilical cord is not hiding and do not include the uterine wall in the measurement

Oligohydramnios

< 5 cm with the largest pocket of 2 cm or less

fluid pocket of < 1-2cm may represent IUGR

Polyhydramnios

> 22 cm with the largest pocket of 8 cm or more

occurs if the fetus cannot swallow

Premature aging of the placenta may contribute to:

oligohydramnios and IUGR

Non-stress test (NST)

uses doppler to record fetal heart rate and its reactivity to the stress of uterine contractions

time period is usually 40 minutes

fetal motion is detected as a rapid rise on the recording of uterine activity or the patient noting fetal movements

Normal NST

two fetal heart rate accelerations of 15 beats per minute or more

accelerations last at least 15 seconds

gross fetal movements are noted over 20 minutes without late decerations

Doppler ultrasounds assess:

umbilical artery

middle cerebral artery

ductus venosus (umbilical vein to IVC)

2 types of doppler

continuous wave (CW)

pulsed wave (PW)

Continuous wave (CW)

single transducer has two separate piezoelectric crystals

*one continuously transmits signals

*one simultaneously receives signals

measures no specific range or depth resolution, but measures all velocities along the designated line of interrogation

Pulsed wave (PW)

short bursts of ultrasound energy emitted at regular intervals

same piezoelectric crystal both sends and receives the signal

allows for depth and range

assumes the constant speed of time (1540 m/s)

** allows for sampling of vessels at specific anatomic locations

PSV

peak systolic velocity

max cardiac contraction

EDV

end diastolic velocity

cardiac relaxtion

Quantitative vs. qualitative measurements

quantitative: includes measurements like blood flow and velocity

qualitative: look at the characteristics of the waveform that indirectly approximate flow and resistance to flow

If something needs more blood, it will be ____ resistive

low

Less diastolic flow =

less blood volume

***HIGH RESISTIVE

More diastolic flow =

more blood volume

***LOW RESISITIVE

S/D ratio

systolic to diastolic ratio

measures peak systolic to end diastolic blood flow

Resistance index (RI)

systole - diastole / systole

Pulsatility index

peak systole - end diastole / mean of the max frequency over the whole cardiac cycle

Umbilical artery doppler measurement

S/D ratio of > 3.0 after 30 weeks is abnormal (high resistive)

normally low resistive

Middle cerebral artery doppler measurement

decreased RI and accelerated velocities are abnormal (high resistive)

head sparing: becomes less restrictive to get the brain more blood

Ductus venosus (umbilical vein) doppler measurement

venous pulsations in the first trimester are normal

second and third trimesters, pulsations should transition to continuous waveform

Maternal uterine artery doppler measurement

assessed after 20 weeks

S/D ratio should be < 2.6

PI should be < 95%

Earliest sign of IUGR

notching visualized after 24 weeks of gestation in the maternal uterine artery

Maternal uterine artery location

branch of the internal iliac artery

crosses over the external iliac vessels ANTERIORLY

Macrosomia

defined as a birth weight of 4000 g or greater or above the 90th percentile for its estimated gestational age

on ultrasound: abdominal skin thickening

EFW: above the 90th percentile

With respect of delivery, any fetus:

too large for the pelvis which it must pass is macrosomic

Macrosomia risk factors

poorly controlled maternal diabetes mellitus

multiparity

advanced maternal age

excessive maternal weight gain and/or obesity

post-term delivery

history of large for gestational age fetus

MOST COMMON risk factor of macrosomia

poorly controlled maternal diabetes mellitus

25-45%

increased levels of glucose and other substrates result in fetal hyperinsulinemia

Macrosomia has an increased incidence of fetal morbidity and mortality as a result of:

head and shoulder injuries and cord compression during delivery

clavicular fractures

facial and brachial palsies

meconium aspiration (sunny side up)

perinatal asphyxia

neonatal hypoglycemia

3 types of macrosomia

fetus that is generally large

fetuses that are generally large but with especially large shoulders (diabetics)

fetuses with a normal trunk but a large head (genetic or pathologic process)

Diabetic mothers may accumulate more:

amniotic fluid (polyhydramnios) vs. nondiabetic mothers

Presence of polyhydramnios in nondiabetic mothers:

alerts to the presence of undiagnosed maternal glucose intolerance

associated with neural tube defects

Placentas of a macrosomic fetus can be:

significantly thick and large

>5 mm is considered thick