Fetal Growth Flashcards
How can you measure the baby?
from the top to the bottom (crown-rump length) at each GA
- There is a period of acceleration of growth, followed off by plateauing at the end of the pregnancy
If we are only using data from failed pregnancy, there will be a large amount of inaccuracy - one of the causes of miscarriage is foetal growth restrictio
What is fetal growth?
increase in mass that occurs between end of embyonic period and birth
What does fetal growth depend on?
Genetic potential
- Derived from both parents
- Mediated through growth factors e.g. insulin like growth factors
Substrate supply
- Essential to achieve genetic potential
- Derived from placenta which is dependent upon both uterine and placental vascularity
What are the phases of normal fetal growth?
- Cellular hyperplasia – increased cell division (happens rapidly in the first few weeks)
- Hyperplasia and hypertrophy – increase in cell size
- Hypertrophy alone
Describe the changes in weight gain
14-15 weeks: 5g /day
20 weeks: 10 g/day
32-34 weeks: 30-35g/day
>34 weeks: growth rate decreases
How can fetal size be assessed ante-natally?
palpating the maternal abdomen and measuring the uterus size; using a tape measure technique (symphysis fundal height – the length from the pubic symphysis, to the fundus of the uterus)
What should the results of SFH be?
12 weeks: at symphysis pubis 20 weeks: at umbilicus 20-34 weeks: GA +/- 2 cm 36-38 weeks: GA +/- 3 cm >38 weeks: GA +/- 4 cm
Why might a baby measure smaller?
- We have the wrong dates
- The baby is small for gestational age
- Oligohydramnios
- Transverse lie
Why might by the baby be larger?
- We have the dates wrong
- Molar pregnancy
- Multiple gestation
- Large for gestational age
- Polyhydramnios
- Maternal obesity
- Fibroids
What are the pros and cons of SFH?
Pros of SFH: SIMPLE and INEXPENSIVE
Cons of SFH:
- Low detection rate: 50-86%
- Great inter-operator variability
- Influenced by a number of factors (BMI, foetal lie, amniotic fluid, fibroids)
How do you date a pregnancy?
date all pregnancies using the crown rump length (CRL)
- Exception: in IVF, we do not use CRL (we know exactly when the embryos were made)
After 14 weeks (after baby has a CRL of >84 mm), CRL becomes inaccurate
- We then use the head circumference – this is used particularly if the first scan is after 14 weeks
What is the importance of correct dating?
- SGA or LGA confusion
- Inappropriate inductions
- Steroids in pre-term delivery
How is fetal growth assessed?
- Bi-parietal diameter (BPD): distance between the two sides of the head
- Head circumference (HC)
- Abdominal circumference (AC)
- Femur length (FC)
What factors influence fetal growth?
MATERNAL FACTORS:
Poverty, Age (higher age increases risk of still birth), Drug use, Weight (low BMI can result in a small baby), Disease (hypertension, diabetes, coagulopathy), Smoking and nicotine, Alcohol, Diet, Prenatal depression, Environmental toxins.
FOETO-PLACENTAL FACTORS:
Genotype – genetic potential, Gender (B>G), Hormones, Previous pregnancy (if a mother has had a previously affected pregnancy with intra-uterine growth restriction, she is at a higher risk of having it again in subsequent pregnancy)
What are the important fetal hormones? Do they have effects on pregnancy?
Pituitary:
- Somatotrophin - Yes, partly via hepatic factors
- Prolactin - No
- FSH/LH - Yes, via gonadal steroids
Pancreas:
- Insulin - Yes – it controls the cell number by having a direct mitogenic affect on cellular development (influences glucose uptake and consumption of glucose in body tissue)
Adrenal glands:
- Androgens - Yes
Gonads:
- Androgens - Yes
Thyroid gland:
- Iodothyronines - Probably by the third trimester
What is a obstetric ultrasound used for?
- Assessment of foetal “wellness” not just size
- Looking at trends in growth
- Predicting foetal metabolic compromise
- Anticipating the need to deliver prematurely
- Liaising with Neonatal Services
What is the definition of SGA?
small for gestational age
an estimated birth weight that is < 10th centile
- WHO defines the small baby as a baby with a birth weight of less than 2.5 kilograms - Using birth weight alone doesn’t take into account the gestational age
What is FGR?
foetal growth restricted (FGR) babies - failure of foetus to achieve its pre-determined potential
What is IUGR?
Intrauterine growth restriction (IUGR) is the most common factor identified in stillborn babies
- In addition, it has serious consequences for babies who survive
- If we can time the delivery better, we can avoid the consequences of still birth
- There is an increased risk of IUGR and intrauterine death in mother’s subsequent pregnancy
What are the short term problems of LBW/FGR/Pre-maturity?
Respiratory distress: particularly if developed before 34 weeks (minimised by giving steroid injections)
- Intraventricular haemorrhage: produces a risk of cerebral palsy later on
- Sepsis: due to an immature immune system
- Hypoglycaemia: if the liver is less developed, you see metabolic problems
- Necrotising enterocolitis: preferential diversion of blood to other places, resulting in ischaemia
- Jaundice
- Electrolyte imbalance
What are the medium and long term effects of LBW/FGR/Pre-maturity?
Medium term: Respiratory problems, Developmental delay, Special needs schooling.
Long term: Foetal programming
What are some factors associated with FGR and SGA fetus?
maternal medical factors:
- chronic hypertension
- connective tissue disease
- severe chronic infection
- diabetes mellitus
- anaemia
maternal behaviour factors:
- smoking
- low booking weight
- poor nutrition
- alcohol
- drugs
fetal factors:
- multiple pregnancies
- structural abnormalities
- chrmosomal abnormalities
- intrauterine infection
placental factors;
- impaired trophoblast invasion
- partia; abruption or infarction
- chorioamnionitis
- placental cysts
- placental praevia
What happens to the placenta?
- 10-12 weeks is the period of placentation
- Rapid early growth prepares way for foetal growth
- Trophoblast cells use same molecular mechanisms as tumors, but are highly regulated and controlled
- The placenta maintains immunological distance between mother and foetus
In a non-pregnant woman, the placenta looks different. The spiral arteries in non-pregnant state sit within the endometrium. In normotensive, normal pregnancy, the spiral arteries open up.
There is a wave of trophoblastic invasion. Trophoblasts invade, to get rid of the muscular wall. There is a funnel shapes, much more dilated vessel, to accommodate the increased amount of blood flow from mother to baby.
What happens in pre-eclampsia toxaemia?
the process of trophoblastic invasion failed. The spiral arteries remain narrow. There is a high shearing force just to get through to the blood supply. This causes ischaemic changes and endothelial imbalance
- commonly associated with babies that are small
- Pre-eclampsia is defined as pregnant women who have hypertension, oedema and proteinuria
- Mild: 140-149/90-99mmHg
- Moderate: 150-159/100-109mmHg
- Severe: ≥160/110mmHg
