normal fetal growth Flashcards
(36 cards)
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
-
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
-
