normal fetal growth Flashcards
What are the main methods of measuring fetal growth?
- crown rump length
- fetal weight
define fetal growth
Increase in mass that occurs between the end of embryonic period and birth
Fetal growth depends on what 2 components:
- Genetic potential
derived from both parents
mediated through growth factors eg insulin like growth factors - Substrate supply
essential to achieve genetic potential
derived from placenta which is dependent upon both uterine and placental vascularity
Normal fetal growth is characterised by 3 subsequent phases:
- Cellular hyperplasia (start of gestation - 20 wks)
- Hyperplasia and hypertrophy (20-28wks)
- Hypertrophy alone (28 - last trimester)
Describe the fetal growth velocity with development
weight gain (rate) increases with time
14-15 wks: 5g /day
20 wks: 10 g/day
32-34 wks: 30-35g/day
>34 wks: growth rate decreases
What is the significance of the symphysis fundal height?
distance over the abdominal wall from the symphysis to the top of the uterus
Why might the SFH be:
a) smaller
b) larger
than normal
Smaller: wrong dates
small for gestational age
oligohydramnios
transverse lie
Larger: wrong dates molar pregnancy multiple gestation large for gestational age Polyhydramnios Maternal obesity Fibroids
What are pros and cons of SFH ?
pros:
Simple
Inexpensive
cons:
Low detection rate: 50-86%
Great inter-operator variability
Influenced by a number of factors (BMI, fetal lie, amniotic fluid, fibroids)
Why is dating the pregnancy accurately important?
SGA or LGA confusion
Inappropriate inductions
Steroids in preterm delivery
–> All pregnancies should be dated by CRL except IVF pregnancies
Why would dating by LMP be inaccurate?
women may have = (irregular periods; abnormal bleeding; oral contraceptives, breastfeeding)
NOTE: All pregnancies should be dated by CRL (crown rump length) except IVF pregnancies
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When is head circumference used to date pregnancy?
if first scan is done after 14 weeks (CRL>84mm)
What are maternal factors influencing fetal growth?
Maternal factors:
- Poverty
- Age (very young / old)
- Drug use
- Weight
- Disease
- hypertension
- diabetes
- coagulopathy
- Smoking and nicotine
- Alcohol
- Diet
- Prenatal depression
- Environmental toxins
What are some feto-placental factor influencing fetal growth?
Feto-placental
- Genotype – genetic potential
- Gender (B>G)
- Hormones
Previous pregnancy
What are some feto-placental factor influencing fetal growth?
Feto-placental
- Genotype – genetic potential
- Gender (Boys > Girl)
- Hormones
Previous pregnancy
The customised standard defines the individual fetal growth potential by three underlying principles:
- Adjusted for maternal constitutional variation
e. g maternal height, weight, ethnicity, parity - Optimised by presenting a standard free from pathological factors such as diabetes and smoking
- Based on fetal weight curves derived from normal pregnancies
-
what is the significance of obstertric ultrasound examination?
Assessment of fetal “wellness” not just size
Looking at trends in growth
Predicting fetal metabolic compromise
Anticipating the need to deliver prematurely
define
SGA
FGR
SGA: Small for Gestational Age
- birth weight < 10th centile
- -> growth at the 10th or less percentile for weight of all fetuses at that gestational age
FGR: Fetal growth restriction
- Failure of the fetus to achieve its predetermined growth potential for various reasons
CHOOSIGN CENTILES
When choosing which centile to use, a balance between sensitivity and specificity is being made – the tenth centile is most sensitive and the third centile is most specific.
-
What are the short term and long term sequelae of FGR?
- Intrauterine growth restriction = most common factor identified in stillborn babies.
increased risk of IUGR and intrauterine death (IUD) in mother’s subsequent pregnancy.
What are some problems of LBW / FGR / Prematurity?
Short term Respiratory distress Intraventricular haemorrhage Sepsis Hypoglycaemia Necrotising enterocolitis Jaundice Electrolyte imbalance
Medium term Respiratory problems
Developmental delay
Special needs schooling
Long term Fetal programming
What are main causes of Small for Gestation Age (SGA) ?
- dating problem
- normal
- fetal problem (e.g fetal abnormality / fetal infection)
- placental insufficiency
What are factors associated with FGR + SGA fetus ?
- Maternal medical factors •Chronic hypertension •Connective tissue disease •Severe chronic infection •Diabetes mellitus •Anaemia •Uterine abnormalities •Maternal malignancy •Pre-eclampsia •Thrombophilic defects
- Maternal behavioural factors •Smoking •Low booking weight (<50 kg) •Poor nutrition •Age <16 or >35 years at delivery •Alcohol •Drugs •High altitude •Social deprivation
- Fetal factors •Multiple pregnancy •Structural abnormality •Chromosomal abnormalities •Intrauterine (congenital) infection •Inborn errors of metabolism
- Placental factors •Impaired trophoblast invasion •Partial abruption or infarction •Chorioamnionitis •Placental cysts •Placenta praevia
NOTE: The first half of pregnancy = time of
preparation for the demands of rapid fetal
growth in the second half
Alterations in maternal physiology facilitate transfer of nutrients to the fetus
-
When is the period of placentation?
10-12 weeks
- rapid early growth –> prepares way fro fetal growth
Why is the placenta important ?
- Maintains immunological distance between mother and fetus
- Special endocrine organ: produces protein-peptides and steroid hormones
- -> also functions as a “transient hypothalamo-pituitary-gonadal axis”
- Responsible for exchange of nutrients, gases & metabolic waste products between maternal and fetal circulation
What is pre-eclampsia ?
Multisystem disease that usually manifests as hypertension and proteinuria
causes in maternal women:
- Hypertension
- Oedema
- Proteinuria
Which fetuses need growth monitoring?
Bad Obstetric History Previous maternal hypertension Previous FGR Stillbirth Placental Abruption
Concerns in index pregnancy
Abnormal serum biochemistry PAPP-A <0.3 MoM
Reduced symphysis fundal height
Maternal systemic disease e.g. hypertension, renal, coagulation
Antepartum haemorrhage
Sequence of events in FGR
there will be
- reduced FM
- decrease in middle cerebral artery blood flow
- increase in ductus venous blood flow –> IUD
NOTE: Increased impedance in the umbilical arteries becomes evident –> only when at least 60% of the placental vascular bed is obliterated
-
What might be the effect of hypoxia on the fetus?
a) Aortic body chemoreceptor Stimulation
- -> causes Redistribution of cardiac output
–> Increased flow to:
Brain
Heart
Adrenals
Decreased flow to:
Lungs
Kidneys
Gut
b) CNS dysfunction Poor tone Altered breathing Altered movement patterns Changes in heart rate patterns
fetal movement counting
- using Cardiff kick chart
- Mothers record the time taken each day to feel ten fetal movements.
- -> reduction / absence in fetal movements,
- -> need cardiotocography + ultrasound assessment of the fetus
How would you Deliver in pregnancies complicated by FGR
Corticosteriods should be administered (if not already given) at gestations < 36 weeks in orderto improve neonatal wellbeing
- Aim to deliver when ≥28 weeks and / or ≥500g
Caesarean section for compromised fetuses
The mode of delivery of FGR will depend upon:
Gestation of the pregnancy Condition of the pregnancy State of the cervix Presentation of the fetus Other factors: oligohydramnios labour may be poorly tolerated due to cord compression
compare between Early IUGR and Late IUGR
early IUGR
- Low incidence 1%
- Highly correlated to maternal disease (preeclampisa)
- Difficult to manage
- Balancing risks of severe prematurity and morbidity with risk of in utero death
Late IUGR
- More common 5-7%
- Rarely correlated to pre-eclampisa
- Difficult to differentiate from constitutionally SGA
- Easy to manage: deliver
Fetal growth restriction is NOT associated with:
A High resistance umbilical artery Doppler readings
B Preterm delivery
C Increased risk of delivery by Caesarean section
D Neonatal hyperglycaemia
E Neonatal necrotising enterocolitis
D Neonatal hyperglycaemia
