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