2. Fetal growth and abnormalities of human development Flashcards
How does foetal growth change through pregnancy?
Period of acceleration of growth, followed off by plateauing at the end
How does foetal weight change through pregnancy?
Gradually increases at start, but the majority occurs in the second half of pregnancy
Why may it not be useful to use data for foetal growth and weight from failed pregnancies?
One of the causes of miscarriage is foetal growth restriction - there will be large amounts of inaccuracies
When is the majority of organogenesis completed?
Week 12
What can an interruption in placental development in the early and late stages cause?
Early - early onset foetal growth restriction
Late - reduced foetal weight gain
What 2 components does foetal growth depend on?
- Genetic potential (mediated through growth factors) e.g. if both parents are tall
- Substrate supply - derived from placenta, dependent on uterine and placental vascularity
What 3 phases characterise normal foetal growth (in terms of cells)?
1) Cellular hyperplasia - increased cell division, 4-20 weeks
2) Hyperplasia and hypertrophy - increased cell size, 20-28 weeks
3) Hypertrophy - also accumulation of muscle, fat and connective tissue, last trimester
In which trimester does the vast majority of growth take place?
3rd trimester (but tailing off of foetal growth velocity at 34 weeks)
How does the maternal store of adipose and glucose change?
Increases vastly (after 20-week mark)
How can foetal size be assessed ante-natally?
• Palpating the abdomen
• Measure the uterus
- tape measure technique - symphysis fundal height
- distance over the abdominal wall from the symphysis to the top of the uterus
• Ultrasound
How does the symphysis fundal height change with time?
Correlates with the number of weeks, but gains more variability closer to term
Why might a baby be measured as smaller than usual?
- Wrong dates
- Small for gestational age
- Oligohydramnios (less fluid)
- Transverse lie
Why might a baby be measure as larger than usual
- Wrong dates
- Large for gestational age
- Polyhydramnios
- Molar pregnancy
- Multiple gestation
- Maternal obesity
- Fibroids
What are the pros and cons of symphysis fundal height?
Pros
• Simple and inexpensive
Cons
• Low detection rate
• Great inter-operator variability
• Influenced by a number of factors
How can you date the pregnancy?
- Ask the mother for the first day of her last menstrual cycle (inaccurate e.g. abnormal bleeding)
- Better to use the crown rump length (CRL) - except in IVF, as we know when the embryos were made
- Use head circumference after 14 weeks, as CRL becomes inaccurate
What 4 biometrical parameters are combined to give the estimated foetal weight (EFW), to assess foetal growth?
- Bi-parietal diameter (BPD) - distance between the two sides of the head
- Head circumference (HC)
- Abdominal circumference (AC)
- Femur length (FC)
What maternal factors can influence foetal growth?
- Poverty
- Age
- Drug use
- Weight
- Disease
- Smoking
- Alcohol
- Prenatal depression
- Environmental toxins
What foeto-placental factors can influence foetal growth?
- Genotype
- Gender
- Hormones
- Previous pregnancy (previous intra-uterine growth restriction can increase risk in next pregnancy)
Does prolactin affect pregnancy?
No
Does insulin affect pregnancy?
Yes - controls the cell number (direct mitogenic affect, influencing glucose uptake and consumption)
Do iodothyronines affect pregnancy?
Probably by third trimester
What 3 principles does the customised standard define individual foetal growth potential by?
- Adjusted to reflect maternal constitutional variation
- Free from pathological factors
- Based on foetal weight curves derived from normal pregnancies
What is macrosomia?
Abnormality that is larger than usual
What is neonatal hydrocephalus?
Baby has a very large head, with extra fluid in the brain
What is achondroplasia?
Child has a normal trunk, but short limbs
What is the most sensitive and specific centile?
- Sensitive (false positives) - 10th
* Specific (false negatives) - 3rd
Why is the 10th centile sensitive (false positives)?
- Will capture all babies with foetal growth restriction
* But this also includes babies that are just small for GA
Why is the 3rd centile specific (false negatives)?
All babies in the 3rd centile will have foetal growth restriction, but some may be missed
What is the definition for small for gestational age?
Estimated birth weight that is <10th centile
What is the most common factor identified in stillborn babies?
Intrauterine growth restriction
can be avoided if we time the delivery better
What are the short term problems of LBW/FGR/pre-maturity?
- Respiratory distress
- Intraventricular haemorrhage (bleeding in brain) - risk of cerebral palsy
- Sepsis - due to immature immune system
- Hypoglycaemia - undeveloped liver
- Necrotising enterocolitis - diversion of blood to other places
- Jaundice
- Electrolyte imbalance
What are the medium term problems with LBW/FGR/pre-maturity?
- Respiratory problems
- Developmental delay
- Special-needs schooling
What are the long term problems with LBW/FGR/pre-maturity?
- Ischaemic heart disease
- Congenital heart diseases
- Diabetes
What are the causes of small gestational age?
- Placental insufficiency (20%)
- Foetal problem (5%) e.g. chromosome abnormality, congenital infection
(Most are normal and not dated properly)
When is the period of placentation?
10-12 weeks
What are trophoblasts?
- Cells forming the outer layer of a blastocyst
- Provide nutrients to the embryo and develop into a large part of the placenta
- Invade the placenta, to get rid of the muscular wall
- Same molecular mechanisms as tumours, but are highly controlled
What is the placenta?
- Special endocrine organ (produces peptide and steroid hormones)
- Functions as a transient hypothalamo-pituitary-gonadal axis
- Responsible for exchange of nutrients, gases and waste
- Maintains immunological distance
How does the placenta look like in a non-pregnant woman compared to a pregnant woman?
- Non-pregnant - spiral arteries sit within the endometrium
* Pregnant - spiral arteries open up (trophoblasts form a funnel shape)
What happens to the placenta in pre-ecamptic toxaemia (PET)?
- Trophoblastic invasion has failed
- Spiral arteries remain thick and narrow
- Ischaemic changes and endothelial imbalance - less blood to the baby
What 3 things define pre-eclampsia in a pregnant woman?
- Hypertension (on 2 separate occasions)
- Oedema
- Proteinuria (over 24 hours)
What is foetal growth restriction without pre-eclampsia called?
Foetal syndrome
What kind of babies is pre-eclamptic toxaemia associated with?
Small babies
When does pre-eclampsia usually occur?
After the 20th week of gestation
What obstetric history factors signal for current foetus monitoring?
- Maternal HT
- FGR
- Stillbirth
- Placental abruption
What is screened for in ‘at risk’ pregnancies at 24 weeks?
- PAPP=A < 0.4 MoM - Down’s syndrome
- Maternal systemic disease e.g. HT
- Uterine artery Doppler ultrasound (check for higher resistance flow)
What happens to the amniotic fluid if the placenta fails?
- Higher resistance in umbilical artery
- Baby stops growing - reduction in foetal movements
- Blood diverted to vital organs
- Less blood to kidneys
- Less urine contribution to amniotic fluid
- Less amniotic fluid
Baby needs to be taken out to prevent intrauterine death
When does increased impedance in the umbilical arteries become evident?
When at least 60% of the placental vascular bed is obliterated
What is the umbilical vein?
Vein that carries oxygenated blood from the placenta to the foetus
Where does 25% of blood flow from the umbilical vein go to?
Ductus venosus (shunts flow to the inferior vena cava, bypassing the liver so more blood goes to the brain)
Why is foetal movement important?
- Reduction in movements may priced foetal death by a day or more
- Counting may be of value in assessing foetal wellbeing
What is the most commonly used method to measure foetal movements?
Cardiff kick chart
What medication should be administered at gestation <36 weeks if there is FGR?
Corticosteroids
How can intra-uterine growth restriction (IUGR) be defined into 2 categories?
Early IUGR
• Low incidence
• Correlated to maternal disease e.g. pre-eclampsia
• Difficult to manage
Late IUGR
• More common
• Rarely correlated to pre-eclampsia
• Easy to manage
What are the symptoms of pre-eclampsia?
- Blurred vision
- Headache
- Swelling in hands and feet
What are the risk factors for pre-eclampsia?
- Previous history
- Multiple gestations
- Hypertension, diabetes, kidney disease
What are the risks for the foetus in pre-eclampsia?
- Stillbirth
- FGR
- Pre-term delivery
How do you deal with FGR?
- Monitor foetus and mother
- Try deliver after 28 weeks, but deliver early if needed
- Corticosteroids if less than 36 weeks
What is the long term maternal consequences for pre-eclampsia?
- Stroke
* Cardiovascular disease
