Foetal growth Flashcards
What simple method can be used to assess fetal growth? What are the advantages of this method?
Symphysis fundal height: distance over abdominal wall from pubic symphysis to top of uterus
Simple + Inexpensive
What are the disadvantages of Symphysis fundal height measurements?
Low detection rate: 50-86%
Subjective
Influenced by various factors:
BMI, Fetal lie, amniotic fluid levels, fibroids, wrong LMP date, multiple pregnancy
Fetal weight continues to increase during pregnancy, while length changes less in later stages.
What measure of foetal size is ultrasound used to determine?
Crown-rump length until 14 weeks, then head circumference
Recall the 4 factors that are combined to estimate foetal weight
Biparietal (head) diameter
Head circumference
Abdominal circumference
Femur length
What 2 overarching factors influence foetal growth?
Genetic potential: derived from both parents, mediated through growth factors
Substrate supply: sufficient nutrients derived from placenta dependent on uterine + placental vascularity
Define pre-eclampsia
Hypertension + proteinuria after 20th week of gestation in a previously normotensive woman + resolving completely by 6 weeks postpartum
What is the optimum age for child bearing?
16-35
What is the main risk to the foetus when the mother has pre-natal depression?
Maternal cortisol levels
What is the effect of IGF on foetal growth
Increases mitotic drive + nutrient availability
What is the role of cortisol in foetal development?
Acts as a TF
Regulates the transition from foetal to adult modes of development
What is the definition of IUGR / FGR?
Failure of infant to reach its predetermined genetic potential for a variety of reasons
What is the definition of SGA?
Birth Weight < 10th centile
Recall the pathophysiology of pre-eclampsia
Hypetension causes high shear force reaching placenta
High resistance in umblicial artery
Baby stops moving, diverts blood to try + compensate
What is a red flag on ultrasound for pre-eclampsia?
Lack of foetal movement
How do the centiles of birth weight charts range?
3rd centile: most specific (all captured have FGR, but some may be missed- false negatives)
10th centile: most sensitive (captures all FGR babies, but also those that are SGA- false positives)
When should the term FGR be used?
For foetuses with definite evidence that growth has been altered
What is IUGR? What are the consequences?
Intrauterine growth restriction
IUGR= most common cause of stillborns
Serious consequences for surviving babies
Further increased risk of IUGR in future pregnancies
List 7 short term problems arising from low birth rate/ prematurity
Respiratory distress Intraventricular haemorrhage Sepsis Hypoglycaemia Necrotising enterocolitis Jaundice Electrolyte imbalance
List 3 medium term problems arising from low birth rate/ prematurity
Respiratory problems
Developmental delay
Special needs schooling
What long term problem may arise from low birth rate/ prematurity?
Fetal programming
Why is Ultrasound the preferred mode of imaging for assessing fetal growth?
No ionising radiation, so safer
Cheaper
What could incorrect dating of pregnancy lead to?
Inappropriate identification of SGA or LGA
Inappropriate decisions about delivery timings + methods
List 4 uses of obstetric ultrasound examination
Assessment of fetal “wellness” not just size
Looking at trends in growth
Predicting fetal metabolic compromise
Anticipating need to deliver prematurely
Describe the use of centile charts for measuring foetal growth
Each parameter is expected to follow a centile, showing steady increases in size
Centiles allow compensation for different sizes of infants that are growing and developing normally.
What limitation must be considered when using centile charts?
None of these measurements take parental characteristics into account, so theres no consideration of the importance of genetic factors.
What are customised foetal growth charts based on?
Fetal weight curves for normal pregnancies.
Adjusted to reflect maternal constitutional variation e.g. maternal height, weight, ethnicity
Optimised by presenting a standard free from pathological factors e.g. diabetes + smoking.
Define fetal growth
Increase in mass occurring between the end of embryonic period + birth
What characterises the 3 stages of foetal growth?
- Cellular hyperplasia (4th-20th week, increase cell numbers)
- Hyperplasia + hypertrophy (20-28th week, increase cell size)
- Hypertrophy alone (28th-40th rapid increase in cell size, fat, muscle, connective tissue)
List 5 maternal factors influencing fetal growth
Poverty: malnourished, uneducated, risky behaviour Age: Extremes Drug/ Smoking/ Alcohol use Diet + weight Disease
List 4 feta-placental factors influencing fetal growth
Genotype (determining genetic potential)
Gender (B>G)
Fetal hormones e.g. cortisol
Previous pregnancy (2nd > 1st)
How can early IUGR be detected?
Fetal size
Umbilical doppler showing abnormal fetal blood flow
What is the definition of LBW?
< 2500g at delivery (accounting for GA)
What are the definitions of VLBW and ELBW?
VLBW: < 1500g at delivery
ELBW: < 1000g at delivery
Don’t account for GA, just account for weight at delivery
Why is it important to distinguish between LBW due to preterm birth and FGR babies?
FGR babies are at greater risk of morbidities + mortalities
List 3 maternal medical factors associated with IUGR
Chronic hypertension
Pre-eclampsia
Diabetes mellitus
List 3 maternal lifestyle factors associated with IUGR
Smoking/ alcohol/ drugs
Low booking weight <50kg / malnutrition
Age <16 or >35 at delivery
List 3 fetal factors associated with IUGR
Multiple pregnancy
Chromosomal abnormalities
Inborn errors of metabolism
List 3 placental factors associated with IUGR
Impaired trophoblast invasion
Partial abruption/ infarction
Chorioamnionitis
Why is there a strong association between pre-eclampsia + IUGR?
Main cause of pre-eclampsia is diminished remodelling of spiral arteries by cytotrophoblast, which causes decreased blood flow + hence decreased nutrient supply to placenta + fetus.
What unmodifiable maternal factors may increase risk of IUGR?
Poor obstetric history
Strong family history
Primips
List 4 indications of IUGR
Abnormal serum biochemistry
Reduced SFH
Maternal systemic disease e.g. HT, renal, sickle
Uterine artery Doppler: blood flow through uterine arteries: identify high resistance flow
How can detection of FGR change plan for delivery? What balance influences timings of delivery in the case of FGR? How is delivery performed?
Aim to deliver when ≥28 weeks +/or ≥500g
Risks to fetus if it remains in utero vs. hazards from prematurity
Caesarean section for compromised fetuses
Describe 3 characteristics of early IUGR
Low incidence 1%
Highly correlated to maternal disease (e.g. preeclampisa)
Difficult to manage: Balancing risks of severe prematurity + morbidity with risk of in utero death
Describe 3 characteristics of late IUGR
More common 5-7%
Rarely correlated to pre-eclampisa
Difficult to differentiate from constitutionally SGA or placental failure
Easy to manage: deliver at 30 weeks
