Reproduction 4 - Fetal Growth Flashcards
1
Q
How can size of the fetus be determined?
A
- Perhaps the simplest to understand are attempts to determine the size of the infant by palpation of the maternal abdomen.
- This is the basis of determination of the Symphysis Fundal Height (SPH)
- Distance between the pubic symphysis and the top of the uterus
- After 20 weeks should be same in cm as the number of weeks
- At 20 weeks at symphesis puis, 20 weeks at umbilicus
2
Q
What may cause lower values in symphysis fundal height?
A
- Wrong last menstrual period date
- The baby in a transverse lie
- Complications (including oligohydramnios (low levels of amniotic fluid) or a baby that is small for gestational age (SGA))
3
Q
What may cause higher values in symphysis fundal height?
A
- Wrong last menstrual period date
- Multiple pregnancy
- Maternal obesity
4
Q
List complications of large symphysis fundal height
A
- Molar pregnancy
- Fibroids
- Polyhydramnios
- A baby that is large for gestational age
5
Q
List pros and cons of symphysis fundal height
A
- May identify gross changes in size, and hence gross complications in the pregnancy (simple and inexpensive)
- Is generally of limited use, thanks to the many confounders, such as considerable inter-operator variability, BMI, fetal lie, amniotic fluid and fibroids
6
Q
List components responsible for the extent of fetal growth
A
- Genetic potential: this is derived from both parents, as taller parents have larger babies. This will be mediated by factors under genetic control, including mediators such as the insulin-like growth factors.
- Substrate supply: sufficient nutrients are essential to achieve genetic potential. This is primarily based on the placenta which is dependent upon both uterine and placental vascularity.
7
Q
How is fetal growth assessed on ultrasound?
A
- Crown rump length (CRL)
- Biparietal diameter (BPD)
- Head Circumference (HC) - used if after 14 weeks or large value for CRL)
- Abdominal Circumference (AC)
- Femur Length (FL).
- Combined to give the Estimated Fetal Weight (EFW).
- Changes in time plotted to visualise the growth over time. Expected to follow a centile (allows compensation for infants of different sizes)
8
Q
Why are customised fetal growth charts used?
A
- They are based on fetal weight curves for normal pregnancies.
- The are adjusted to reflect maternal constitutional variation e.g. maternal height, weight, ethnicity, parity.
- They are optimised by presenting a standard free from pathological factors such as diabetes and smoking.
- Based on normal pregnancies
9
Q
What is the average velocity an infant gains weight?
A
14-15 wks: 5g /day
20 wks: 10 g/day
32-34 wks: 30-35g/day
> 34 wks: growth rate decreases
10
Q
List the phases in normal fetal growth
A
- Cellular hyperplasia (rapid cell division and hyperplasia): 4-20 weeks
- Hyperplasia and hypertrophy (increased cell size, cell division declines): 20-28 weeks
- Hypertrophy dominates: 28-40 weeks (rapid increase in cell size, and increase in muscle, fat and connective tissue)
11
Q
List confounding factors for reliability of the last menstrual period
A
- Irregular length of periods
- Abnormal endometrial bleeding
- The use of oral contraceptives; breastfeeding.
12
Q
Why is dating of birth important?
A
- May lead to a pregnancy being inappropriately identified as large or small for gestational age.
- Clinical decisions about delivery timings and methods (induction or Caesarean section) may not be correct, eg. glucocorticoids are given prior to preterm delivery to enhance lung surfactant production and subsequent lung function.
13
Q
What is best practice for dating pregnancy?
A
- Ultrasound, determining the Crown-Rump length (CRL) of the fetus, measuring from the top to bottom.
- Preferably towards the end of the first trimester
- Used in all pregnancies except IVF
14
Q
List maternal factors influencing fetal growth
A
- Poverty (more likely to have children at a younger age, less aware of risks of factors affecting growth rates, malnutrition)
- Mothers age
- Drug use
- Alcohol
- Smoking and nicotine
- Diseases (placenta cannot filter out all pathogens, hypertension, diabetes and coagulopathy)
- Mothers diet and physical health (eg. lack of iron and anaemia, lack of calcium and poor bone formation, lack of protein and mental retardation)
- Mothers prenatal depression (slower fetal growth rate)
- Environmental toxins (eg. lead, mercury and ethanol)
15
Q
How does mothers age affect fetal growth?
A
- Women over 35 are more inclined to have a longer labour period, which could potentially result in death of the mother or fetus.
- Women under 16 and over 35 have a higher risk of preterm labour (premature baby), and this risk increases for women in poverty, African Americans, and women who smoke.
- Young mothers are more likely to engage in high risk behaviors
- Premature babies from young mothers are more likely to have neurological defects that will influence their coping capabilities – irritability, trouble sleeping, constant crying for example.
- There is increased risk of Down syndrome for infants born to those aged over 40 years.
16
Q
How does drug use affect fetal growth?
A
- Maternal drug use occurs when drugs ingested by the pregnant woman are metabolized in the placenta and then transmitted to the fetus.
- When using drugs (narcotics), there is a greater risk of birth defects, low birth weight, and a higher rate of death in infants or stillbirths.
- Drug use may lead to extreme irritability, crying, and risk for SIDS once the fetus is born, as well as causing addiction
- Marijuana will slow fetal growth rate and can result in premature delivery.
- Heroin will cause interrupted fetal development, stillbirths, and can lead to numerous birth defects. (SIDS, miscarriage, abnormal neurological functions)
- Cocaine use results in a smaller brain and learning disabilities for the fetus. Risk of being stillborn or premature. Cocaine use also results in low birthweight, damage to the central nervous system, and motor dysfunction.
17
Q
How does alcohol affect the foetus?
A
- Disruptions of the fetus’s brain development, interferes with the fetus’s cell development and organization, and affects the maturation of the central nervous system.
- Alcohol use can lead to heart and other major organ defects, such as small brain, which will affect the fetus’s learning behaviors.
- Alcohol use during pregnancy can cause behavioral problems in a child, mental problems or retardation and facial abnormalities – meaning smaller eyes, thin upper lip, and little groove between the nose and lips. Use can also increase the risk of miscarriages and stillbirths, or low birth weight.
18
Q
What is fetal alcohol syndrome?
A
- Fetal alcohol syndrome (FAS) is a developmental disorder that is a consequence of too much alcohol intake by the mother during pregnancy.
- Children with FAS have a variety of distinctive facial features, brain abnormalities, and cognitive deficits.
19
Q
How does smoking and nicotine affect the fetus?
A
- When a mother smokes during pregnancy the fetus is exposed to nicotine, tar, and carbon monoxide.
- Nicotine results in less blood flow to the fetus because it constricts the blood vessels. (also increases risk of miscarriage)
- Carbon monoxide reduces the oxygen flow to the fetus.
- The reduction of blood and oxygen flow results in stillbirth, low birth weight, and ectopic pregnancy. There is an increase of risk of sudden death syndrome (SIDS) in infants.
- There has been a link from smoking during pregnancy that led to asthma in childhood.
20
Q
List the feto-placental factors influencing fetal growth
A
- Gender (males bigger than females)
- Hormones
- Genotype
- Previous pregnancy
21
Q
How do hormones affect fetal growth?
A
- Insulin increases mitotic drive and nutrient availability
- Cortisol affects tissue differentiation and maturation (alteration of gene transcription, induces switch from IGFII to IGFI)
- Thyroxine affects tissue accredition and differentiation
- IGFs are mitogenic, stimulating fetal metabolism. IGFII regulates early embryonic development
- Glucocorticoid affects tissue differentiation and prenatal development of organs
- EGFs, TGFs, FGFs, interleukins 1 and embryoinic cholinesterases are all important
- Somatotrophin has a small effect
22
Q
Define small for gestational age
A
Infant birth weight below 10th centile (also uses fifth or third centile)
23
Q
Define intrauterine growth restriction
A
Failure of the infant to achieve predetermined potential (IUFR)
24
Q
Define low birthweight
A
Less than 2.5kg at delivery (can be normal or with presence of fetal growth restriction, where c-section is needed)
25
Q
Define very low birth weight
A
Less than 1.5kg at delivery
