fetal growth Flashcards
what is the most simple test to determine size of infant
palpation OF HUMAN ABDOMEN
Symphysis Fundal Height
(istance between the pubic symphysis and the top of the uterus)
Changes in SPH with gestational age reflects ……
generic changes in uterine size but it is vulnerable to a variety of errors
SPH lower than they should be may result from
wrong last menstrual period date
transverse lie
oligohydramnios
SPH higher than they should be may result from
wrong last menstrual period
multiple pregnancy
maternal obesity
Initial information on the actual size of the fetus was based on…
miscarriages
did not take account of the possible causative relationship between low fetal growth leading to miscarriage
Two primary components responsible for the extent of fetal growth are…
Genetic potential
substrate supply
describe how genetic potential contributes
derived from both parents
reflects the logical view that taller/ bigger parents will have infants that are different in size to parents who are shorter or lighter in build.
Mediated by factors under genetic control.
describe how substrate potential contributes
sufficient nutrients are essential to achieve genetic potential.
Primarily based on placenta.
define Fetal Growth
increase in mass that occurs between the end of the embryonic period and birth.
Fetal growth is assessed by 4 biometrical parameters….
biparietal diameter (BPD)
head circumference (HC)
abdominal circumference (AC)
femur length (FL).
what are these 4 biometrical parameters combined to give
estimated fetal weight (EFW).
what curves are plotted from these biochemical markers
Normative growth curves have been constructed from these ultrasound measurements (expressed in centiles).
what are these biochemical markers used to identify clinically
normal intrauterine growth
detect risk of obstetric and neonatal complications.
why is the use of centiles important
allows compensation for different sizes of infants that are growing and developing normally
allows plot of serial measuremnets
what can be used for more individual assessment of growth
Customised fetal growth charts
based on fetal weight curves for normal pregnancies and adjusted to reflect maternal variation
how are customised Fetal Growth charts optimised
presenting a standard free from pathological factors such as diabetes and smoking.
Normal fetal growth is characterised by three main phases….
Cellular hyperplasia (increased cell numbers): 4-20 weeks
Hyperplasia and hypertrophy (increased cell size): 20-28 weeks
Hypertrophy dominates: 28-40 weeks
Best practice is therefore to date the pregnancy by…
ultrasound
determining the Crown-Rump length
variations in fetal size are more limited at this stage of development
why is Last Menstrual Period (LMP) not as reliable for dating a pregnancy
Confounding factors include:
Irregular length of periods; abnormal endometrial bleeding; the use of oral contraceptives;
also unplanned pregnancies may not take note of LMP
what are possible consequences of incorrect dating
pregnancy being inappropriately identified as Large or Small for gestational age
delivery timings and methods (induction or Caesarean section) may not be correct;
glucocorticoids are given prior to preterm delivery to enhance lung surfactant production and subsequent lung function.
Maternal factors influencing fetal growth
poverty, mother’s age, drug use, alcohol, smoking etc.
name possible mechanisms by which these factors affect growth
predispose to LBW, risk taking behaviour, age = longer labour periods, alcohol affects brain/CNS, increase risk os still birth
name some symptoms of Fetal alcohol syndrome (FAS)
variety of distinctive facial features, brain abnormalities, and cognitive deficits, learning behaviours affected
how can smoking cause issues
Nicotine results in less blood flow to the fetus because it constricts the blood vessels.
Carbon monoxide reduces the oxygen flow to the fetus.
difference between male/female size
Males are generally bigger
second and subsequent infancy pregnancies are…
generally heavier
what Hormones have a role in regulating fetal growth
cortisol, thyroxine, pituitary growth hormone
how do these fetal hormones promote growth and development in utero
altering both the metabolism and gene expression of the fetal tissues.
They ensure that fetal growth rate is commensurate with the nutrient supply
ensure prepartum maturation occurs in preparation for extra-uterine life.
Cortisol effects
Tissue differentiation
Insulin effects
increases mitotic drive and tissue availability for tissue accretion (gradual growth via layer accumulation)
IGF-II to IGF-I
thyroxine effects
tissue differentiation and accretion
IGF1 is responsible for
the growth of the newborn.
what does IGF-II do
regulates early embryonic development
what do Fetal glucocorticoids do
affects tissue differentiation and prenatal development of the organs such as, for example, lungs (maturation of the surfactant)
feto-placental factors affecting growth
Genotype – genetic potential
Gender (B>G)
Hormones
Previous pregnancy
when is growth velocity greatest
mid third trimester (32-34 weeks)
define Low birth weight
Less than 2,500g at delivery
define Small for gestational age (SGA)
The infant has a birth weight <10th centile
