Fetal Growth Flashcards
Outline normal fetal growth
Definition:
Increase in mass that occurs between the end of embryonic period and birth. Assessed by symphysis fundal height (SPH) and ultrasound scans.
SPH: involves palpation of maternal abdomen for gross estimation of uterus height
- Distance between pubic symphysis and fundus of uterus.
- Simple • Low detection rate: 50-86%
- Inexpensive • Great inter-operator variability
• Influenced by a number of factors (BMI, fetal lie, amniotic fluid, fibroids)
- Errors in values achieved:
- Values lower than they should be – wrong LMP date, baby lies in a transverse line, complications including oligohydramnios (low amniotic fluid levels) or baby us small for GA.
- Values greater than they should be – wrong LMP date, multiple pregnancy, maternal obesity.
- Complications include – molar pregnancies, fibroids, polyhydramnios, large baby for GA.
- Historical data on foetal size and hence growth came from miscarriages which data didn’t consider the possible causative relationship between low foetal growth leading to miscarriages – old data may be inaccurate.
- Hence foetal growth and weight measurements have mainly been replaced with in utero scanning data.
Normal foetal growth rates – characterised by three main phases:
- Hyperplasia – 4-20 weeks.
- Hyperplasia and hypertrophy – 20-28 weeks.
- Hypertrophy – 28-40 weeks – hence why mid-third trimester is greatest growth velocity.
Fetal growth velocity: Weight gain
- 14-15 weeks - 5g/day.
- 20 weeks - 10g/day.
- 32-34 weeks - 30-35g/day. Fastest velocity is mid-third trimester.
- >34 weeks - velocity decreases
Imaging: explain why ultrasound is the preferred imaging choice for the assessment of fetal growth and identify the role of ultrasound in the assessment of fetal wellbeing
Dating the pregnancy:
- It is hard to date the pregnancy exactly as there are issues knowing the LMP date (i.e. planned vs. unplanned pregnancies, oral contraceptive use, etc.) but it’s important to get it right to classify GA.
- Best practice to date pregnancy – ultrasound – determining crown-rump length of foetus (end of 1st trimester – variations in foetal size are more limited at this stage so more accurate date).
Ultrasound scanning – US scanning can identify the following
- Biparietal diameter (BD).
- Head circumference (HC).
- Abdominal circumference (AC).
- Femur length (FL).
Combines into Estimated Foetal Weight (EFW).
US is mainly used to assess OVERALL FOETAL WELL-BEING (i.e. chromosomal abnormalities).
Normative growth curves can be obtained from each of these measurements.
- Due to the differences in people, customised foetal growth charts may be used
- Based on foetal weight curves for normal pregnancies.
- Adjusted to reflect maternal constitutional variation – i.e. mother weight.
- Optimised – with curves free from data influenced by pathological factors.
Dating Dating by LMP:
- Inaccurate (irregular periods; abnormal bleeding; oral contraceptives, breastfeeding)
- Importance of correct dating:
- SGA or LGA confusion
- Inappropriate inductions
- Steroids in preterm delivery
All pregnancies should be dated by CRL except IVF pregnancies
Ultrasound assessment of fetal growth
- Fetal growth is assessed by 4 biometrical parameters (BPD, HC, AC, FL) and their combination (EFW)
- Normal growth curves constructed from ultrasound measurements are expressed in centiles
- They are used clinically to identify a normal intrauterine growth and detect risk of obstetric and neonatal complications
Understanding of normal fetal growth facilitates good obstetric management of cases with abnormal fetal growth
Obstetric Ultrasound Examination
- Assessment of fetal “wellness” not just size
- Looking at trends in growth
- Predicting fetal metabolic compromise
- Anticipating the need to deliver prematurely
- Liaising with Neonatal Services
Fetal growth parameters: summarise the uses and limitations of centile charts in the assessment of fetal growth and recall the commonly used fetal growth parameters
Technique of SFH
SFH: distance over the abdominal wall from the symphysis to the top of the uterus
12 w: at symphysis pubis 20 w: at umbilicus 20-34w: GA +/- 2 cm 36-38w: GA +/- 3 cm >38w: GA +/- 4 cm
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
Pros & Cons of SFH • Simple • Inexpensive • Low detection rate: 50-86% • Great inter-operator variability • Influenced by a number of factors (BMI, fetal lie, amniotic fluid, fibroids)
Customised growth chart
The customised standard defines the individual fetal growth potential by three underlying principles:
- Adjusted to reflect maternal constitutional variation maternal ht, wt, 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
Factors influencing fetal growth
Fetal growth depends on 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
Influencing factors of foetal growth:
Maternal factors influencing foetal growth:
- Poverty – more likely to be young (low birth weight) and be less educated on risks.
- Mother’s age – too young or too old can impact baby health.
- Drug use and alcohol.
- Smoking and nicotine.
- Diseases.
- Mother’s diet and physical health – MALNUTRITION is the most important factor in baby growth.
- Mother’s prenatal depression.
- Environmental toxins.
- Anemia, DM
Feto-placental factors:
- Multiple pregnancy, chromosome abnormality, placental preeclampia
- Different genotypes.
- Gender – males tend to be bigger than females.
- Previous pregnancy – infants are heavier in the 2nd and subsequent pregnancies.
- Hormones – one important hormone is IGF-1 that acts to:
- Increase mitotic drive.
- Increase nutrient availability for tissue accretion.
- Little effect on tissue differentiation (this is mediated by cortisol).
Intra-uterine growth restriction (IUGR): define, recall the aetiology of IUGR
Definitions:
SGA – Small for Gestational Age – infant has a birth weight <10th centile (AKA “Small for Dates”)
FGR: Failure of the fetus to achieve its predetermined growth potential for various reasons
LBW – Low Birth-Weight – <2,500g - ~7% of deliveries.
- Epidemiological studies use BW alone, not GA
- Most LBW neonates are NOT growth restricted
- Many FGR babies are delivered prematurely
- 3-10 fold increase in perinatal morbidity and mortality
Fetal Growth Restriction (FGR)
- The term FGR should only be used for fetuses with definite evidence that growth has altered.
- Growth is a dynamic process of a change of size over time and, therefore, it can only be assessed by serial observation.
Choosing 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.
- The tenth centile will capture all babies with FGR, but will also include those babies that are just small for gestational age, i.e. you get a number of false positives.
- All babies recorded using the third centile will have FGR, but some FGR babies may be missed, i.e you get a number of false negatives.
- LBW, FGR and preterm delivery have closely associated pathologies L
10nth sensitive - all babies with growth restriction and those small for gestanional
Explain the management of and summarise the screening and detection used to identify intra-uterine growth restriction (IUGR)
- The term IUGR is only used for definite IUGR babies.
- The growth charts are most useful for displaying serial estimates over time so diagnosis accuracy is higher.
Outcomes of IUGR:
- IUGR is most common cause of still-born babies.
- Subsequent pregnancies may be affected by IUGR.
Causes of IUGR:
Generally, develops in the 2nd and 3rd trimesters as the 1st stage focuses on embryology (up to 50g weight).
Divided into 4 categories:
Maternal medical factors – infection, pre-eclampsia, uterine abnormalities, etc.
Maternal behavioural factors – i.e. alcohol.
Foetal factors – i.e. multiple pregnancy.
Placental factors – i.e. placental cysts, impaired trophoblast invasion.
IUGR and Pre-Eclampsia
There is a close link between IURG and pre-eclampsia.
Due to main cause of pre-eclampsia is diminished remodelling of spiral arteries by cytotrophoblasts. This causes decreased blood flow and hence decreased nutrient supply to the placenta and foetus.
Pre-eclampsia – hypertension and proteinuria.
Occurs in ~5% of pregnancies.
Causes of SGA
SGA
- Dating problem
- Consistant growth
- Normal dopplers and fluid
- Normal
- Growth may reduce in 2 weeks
- Normal dopplers and fluid
- Fetal problem 5%
- Fetal abnormality
- Fetal infection
- Placental insufficiency 20%
- Reduction in AC/FL
- Reduced liquor
- Deranged dopplers
