Women's Health L21: Disproportionate Fetal Growth and Multifetal Gestation

what is the best way to measure fetal size during the 1st trimester?

crown-rump length (CRL)

what are the four standard parameters to measure fetal size and weight in the 2nd and 3rd trimester?

1. biparietal diameter

2. head circumference

3. abdominal circumference

4. femur length

when is fetal weight typically calculated?

after 24 weeks gestation

what is biparietal diameter (BPD)?

the maximum diameter of the transverse section of the fetal skull at the level of parietal eminences

how is head circumference (HC) different than biparietal diameter?

uses a similar transverse section as BPD but measures the full circumference

how is the abdominal circumference (AC) measured?

taken at the level of largest diameter of the fetal liver

how is the femur length (FL) measured?

measures the femur closest to the transducer (the "upside" femur)

what is intrauterine growth restriction (IUGR) also known as?

fetal growth restriction

how is FGR defined if prenatal?

1. estimated fetal weight (EFW)

2. AC < 10th percentile for gestational age

how is FGR defined if postnatal?

1. must meet ≥ 3 criteria

2. birth weight is < 10% percentile

3. head circumference is < 10% percentile

4. prenatal diagnosis of FGR

5. prenatal history of condition is strongly associated with FGR (hypertension, infection, or preeclampsia)

what does it mean for a fetus to be small for gestational age (SGA)?

their birth weight is < 10% percentile for gestational age regardless of the etiology

does being small for gestational age distinguish between those that are small and otherwise healthy from those that are small due to growth resistrction?

no

2 multiple choice options

what is macrosomia?

1. excessive intrauterine growth

2. EFW of > 4000 to 4500 grams (~9-10 lbs)

what does it mean for a fetus to be large for gestational age (LGA)?

birth weight > 90% percentile for gestational age

what are the maternal risk factors for FGR?

1. vascular disease

2. kidney disease

3. diabetes

4. antiphospholipid syndrome

5. tobacco and substance use

6. antiseizure and certain chemotherapy medications

what are the fetal risk factors for FGR?

1. genetic abnormalities

2. congenital anomalies

3. infections (CMV, syphilis, rubella, varicella, toxoplasmosis)

what are the placental risk factors for FGR?

1. placental insufficiency (most common)

2. velamentous cord insertion

3. single umbilical artery

placental insufficiency is a diagnosis of exclusion

true

1 multiple choice option

how do you screen for FGR in low-risk pregnancies?

perform fundal height checks -- if ≥ 4 cm lag, perform an US

what will an US assess when screening for FGR?

1. fetal size

2. estimate fetal weight

3. evaluate placenta

how do you screen for FGR in pregnancies with risk factors?

1. perform an US at 28 weeks to evaluate growth and estimate weight

2. repeat scans based on the results and risk profile

how is FGR diagnosed?

1. based on US evidence of EFW < 10% percentile or AC < 10% percentile

2. if weight or AC is < 3rd percentile

3. oligohydramnios (decreased amniotic fluid volume)

4. abnormal umbilical doppler

what is the goal in managing FGR?

identifying those at high risk of perinatal demise that would benefit from early delivery

how can FGR be managed?

1. US every 2-4 weeks to calculate and track EFW

2. doppler of umbilical artery to assess for abnormal flow

3. non-stress test (NST) or biophysical profile (BPP)

4. antenatal corticosteroids -- betamethasone or dexamethasone

what are the measured variables in a biophysical profile (BPP)?

1. fetal breathing movements

2. gross body movements

3. fetal tone

4. reactive fetal heart rate

5. qualitative amniotic fluid volume

when can antenatal corticosteroids be initiated?

if < 34 weeks of gestation AND preterm birth is anticipated

what do antenatal corticosteroids reduce the incidence of?

newborn respiratory distress syndrome

how is an early delivery determined for FGR?

based on the results of surveillance tests

when is a trial of labor for FGR not acceptable?

unless a standard indication for a C-section is present

what are the neonatal complications of FGR?

1. preterm birth

2. perinatal asphyxia

3. impaired thermoregulation

4. hypoglycemia

5. hypocalcemia

6. hyperbilirubinemia

7. polycythemia

8. feeding difficulties

9. impaired immune function

which neonatal complication has a higher risk of death and prematurity-related morbidity?

preterm birth

3 multiple choice options

which neonatal complication of FGR has a greater risk of hypothermia due to reduced subcutaneous fat and poor nutrient reserves?

impaired thermoregulation

3 multiple choice options

which neonatal complication of FGR has a greater risk of developing when a placental factor is involved?

perinatal asphyxia

3 multiple choice options

which neonatal complication is common in FGR?

hypoglycemia

3 multiple choice options

why might hypocalcemia develop as a neonatal complication of FGR?

decreased calcium transfer across the placenta

how does polycythemia develop as a neonatal complication of FGR?

increased erythropoietin production due to hypoxia

how do feeding difficulties occur as a neonatal complication of FGR?

poor coordination of sucking and swallowing

what are the extrinsic risk factors of macrosomia?

1. maternal diabetes -- gestational or pregestational

2. maternal obesity

3. excessive gestational weight gain

4. post-term pregnancy

5. previous macrosomic infant

what are the intrinsic risk factors of macrosomia?

1. genetic variant

2. familial trait

3. male sex

which type of risk factor for macrosomia is the most common: intrinsic or extrinsic?

extrinsic

3 multiple choice options

what is the consequence of maternal diabetes as a risk factor of macrosomia?

1. results in fetal hyperglycemia

2. leads to a greater release of insulin, growth hormone and fat deposition

which is harder to screen for: macrosomia or FGR?

macrosomia

3 multiple choice options

how do you screen for macrosomia in low-risk pregnancies?

1. no standard screening guidelines

2. routine monitoring of fundal height -- use Leopold maneuver

3. combine clinical findings with an US

how do you screen for macrosomia in pregnancies with risk factors?

1. routine monitoring of fundal height -- use Leopold maneuver

2. perform an US at 37 weeks

how is macrosomia diagnosed?

based on US evidence of EFW > 4000-4500 grams (~9-10 lbs)

which imaging modality is the standard modality despite lack of sensitivity and specificity?

US

2 multiple choice options

what is the goal in managing macrosomia?

identifying those at risk for complicated births who would benefit from a C-section delivery

when should a C-section be offered to patients with macrosomia?

1. EFW is > 5000 g in a patient without diabetes

2. EFW is > 4500 g in a patient with diabetes

what are the neonatal complications of macrosomia?

1. mortality

2. birth injury

3. perinatal asphyxia

4. respiratory distress

5. hypoglycemia

6. polycythemia

7. congenital anomalies

8. hospital readmissions

when is there a 2x risk of mortality in patients with macrosomia?

severe macrosomia (EFW > 5000 g or 11 lbs)

what birth injuries can a fetus with macrosomia be predisposed to?

1. shoulder dystocia

2. brachial plexus injury

3. clavicular fracture

what are the complications of perinatal asphyxia in a fetus with macrosomia?

1. increased intrauterine oxygen utilization due to fetal hyperglycemia

2. likely to have a low 5-minute Apgar score

how does respiratory distress develop as a complication of macrosomia?

a delay in clearance of fetal lung fluid

how does a fetus with macrosomia present if they are in respiratory distress?

transient tachypnea due to C-section delivery

how can hypoglycemia develop as a neonatal complication of macrosomia?

when placental supply of glucose is interrupted at birth

what are some consequences of congenital anomalies as a neonatal complication of macrosomia?

1. hip subluxation

2. hydrocephalus

what are the most common reasons for a neonate with macrosomia would be readmitted to the hospital?

1. infections

2. digestive disorders

3. jaundice

when are hospital readmissions the greatest for a neonate with macrosomia?

within the first month after discharge

what is zygosity?

the genetic makeup for multiple gestations

what is chronicity?

placental composition -- number of placentas

chronicity must be determined early due to the associated risks to the pregnancy

true

1 multiple choice option

what is amnionicity?

number of amniotic cavities

what are the two layers that comprise the fetal membrane that surrounds the fetus during pregnancy?

1. chorion -- thicker outer layer

2. amnion -- thinner inner layer

the chorion and amnion form the amniotic sac

true

1 multiple choice option

what are the types of multifetal gestation?

1. monozygotic

2. dizygotic

what is a monozygotic pregnancy?

1. the division of a fertilized single ovum and sperm

2. identical twins

what dictates the status of the chorion and amnion?

timing of the division

what is a dizygotic pregnancy?

1. two separate ova are fertilized by two separate sperm

2. fraternal twins

how does a dizygotic pregnancy occur?

1. two eggs are released from the ovaries

2. each egg is fertilized by two different sperm

3. each embryo implants in the womb separately

a monozygotic pregnancy is further broken down into which classifications?

1. dichorionic and diamniotic

2. monochorionic and diamniotic

3. monochorionic and monoamniotic

what is a dichorionic and diamniotic pregnancy?

1. separate or fused placentas

2. 2 chorions/amnions

when does a dichorionic and diamniotic pregnancy occur?

the early embryo splits before implanting in the womb

which classification of a monozygotic pregnancy has the lowest rate of complications?

dichorionic and diamniotic

3 multiple choice options

what is a monochorionic and diamniotic pregnancy?

a single placenta with a common chorion but 2 amnions

when does a monochorionic diamniotic pregnancy occur?

the early embryo implants in the womb and then splits

which classification of a monozygotic pregnancy has an increased risk of adverse outcomes?

monochorionic and diamniotic

3 multiple choice options

what is a monochorionic and monoamniotic pregnancy?

a single placenta with one chorion and one amnion

when does a monochorionic monoamniotic pregnancy occur?

the early embryo implants in the womb and then splits later

which classification of a monozygotic pregnancy is the rarest form of twins?

monochorionic and monoamniotic

each fetus in a dizygotic pregnancy will be dichorionic diamniotic

true

1 multiple choice option

what are the maternal complications of a multifetal gestation?

1. hyperemesis gravidarum

2. anemia

3. gestational diabetes

4. vaginal bleeding

5. preeclampsia

6. postpartum depression

what are the fetal complications of a multifetal gestation?

1. prematurity

2. twin-twin transfusion syndrome

3. aneuploidy conditions and congenital anomalies

4. discordant fetal growth

5. fetal demise

6. conjoined twins

what is discordant fetal growth?

a ≥ 20% difference in EFW between the fetuses

in which type of multifetal gestation is there a greater risk for fetal demise?

monochorionic gestations

3 multiple choice options

what is twin-twin transfusion syndrome (TTTS)?

a complication of monochorionic diamniotic gestation

how does TTTS occur?

due to arteriovenous anastomoses and unequal sharing of the placenta between twins, resulting in an imbalance in the direction of blood flow

how does TTTS present?

1. hypovolemia/restriction of one twin and hypervolemia of the other twin

2. monochorionic placentation with discordant amniotic fluid volumes

3. onset is gradual and during mid-2nd trimester

how is TTTS managed?

1. screen with an US, starting in the 2nd trimester

2. monitor with BPPs and cervical length

3. fetoscopic laser ablation of anastomotic vessels if there are signs of progression

4. +/- serial amnioreduction

5. antenatal corticosteroids after 24 weeks of gestation

what are the delivery complications of a multifetal gestation?

1. preterm premature rupture of membranes (PPROM)

2. operative delivery

3. asymptomatic cervical dilation

4. asymptomatic cervical shortening

how is asymptomatic cervical dilation prior to 24 weeks managed?

1. cerclage

2. sutures are placed around the cervical os

how is asymptomatic cervical shortening prior to 24 weeks managed?

if without cervical dilation, use vaginal progesterone

what is the multifetal gestation classification for twin boys?

monozygotic

1 multiple choice option

what is the multifetal gestation classification for twins, one boy and one girl?

dizygotic

1 multiple choice option

what is the multifetal gestation classification of monozygotic twins who share one placenta and one amnion?

monochorionic and monoamniotic

2 multiple choice options

what is the multifetal gestation classification of monozygotic twins with two placentas and two amnions?

dichorionic and diamniotic

2 multiple choice options