normal fetal growth Flashcards
describe fetal growth pattern - length *
rapid growth at the start of the pregnancy that decreases
a lot of miscarriages are due to increased growth restriction
there is little variance up to 16weeks of pregnancy, but considerable variance in mid and late trimester
main cause of fetal growth restriction is diminished supply of nutrients
maternal habitus and physiology influence the babies size - positive correlation between mother’s height, uterine size and placental blood flow
describe weight gain of the fetus *
mainly occurs in mid-late trimester
define fetal growth *
increase in mass that occurs between the end of the embryonic period and birth
timeframe for the development of organs in fetus *
by trimester 1 most of the organs have developed
therefore if there is interruption to placental development - the earlier it is, the earlier you get fetal growth restriction; if it happens later it will cause reduced weight gain towards term
what does normal fetal growth depend on *
genetic potential - from both parents, mediated through GF eg insulin like GF - ie bigger parents will have bigger babies
substrate supply - essential to achieve genetic potential, derived from the placenta that is dependant on uterine and placental vascularity
describe an abnormal placenta *
small and infarcted - limits the nutrients that are given to the fetus
what are the 3 phases of normal fetal growth *
- cellular hyperplasia - 4-20weeks - rapid cell division and multiplication as embryo develops into a fetus
- hyperplasia and hypertrophy - 20-28wks - cell division declines and the cell increases in size
- hypertrophy alone - 28-40wks - increase in cell size, deposition of fat, protein and connective tissue
describe the growth of the organs *
brain, liver, heart and kidneys develop rapidly - there is doubling of DNA each week
the increase in cell size and number of cells decreases towards the end
at term - organs have <20% of cells characteristic of adult - more development is to be done after birth
what is the fetal growth velocity *
14-15 wks: 5g /day
20 wks: 10 g/day
32-34 wks: 30-35g/day
>34 wks: growth rate decreases - not consistant with the miscarriage data, showing it is unreliable
what is the purpose of abdominal plapation in pregnancy *
to determine the size of ther uterus for the stage of pregnancy
find the SFH - distance over the abdominal wall from the symphesis to the top of the uterus
- 12 w: at symphysis pubis
- 20 w: at umbilicus
- 20-34w: GA +/- 2 cm
- 36-38w: GA +/- 3 cm
- >38w: GA +/- 4 cm
reasons why teh SFH might be smaller than it should be *
got the dates wrong
small for gestational age
oligohydramnios - less fluid
transferse lie - the baby is in the wrong position
reasons why SFH is larger than it should be *
wrong dates
molar pregnancy
multiple gestation
large for gestational age
polyhydramnios
maternal obestity
fibroids
benefits and disadvantages of SFH *
+ simple
+ inexpensive
+may identify gross changes in size and hence gross complications in pregnancy
- low detection rate - 50-86%
- inter-operator variability
- influenced by many factors - BMI, fetal lie, amniotic fluid, fibroids
what do you do if the SFH is abnormal *
send for US
problem with dating from the last menstrual period (1st day) *
inaccurate - if have irregular periods, abnormal bleeding, oral contraceptives, breastfeeding
also of an unplanned pregnancy - people might not know the date of LMP
why is it important to date correctly *
so know if short for gestational age (SGA) or LGA
ensure there are not inappropriate inductions if the surfactant hasnt matured properly
so you know that the delievery is preterm and to give steroids
how should you date babies *
crown-rump length at end of 1st trimester preferably - variations in size are more limited at this point so gestational age can be estimated more effectively
except IVF - a 5 day embryo is inserted
head circumference is used if 1st scan is after 14weeks - CRL >84mm
US assessment of fetel growth is done on biparietal diameter, head circumference, arm circumference, femer length, and their combination - estimated fetal weight
how are growth curves expressed and used *
they’re expressed in centiles - important because it allows compensation for babies of different sizes that are growing and developing normally
used to identify normal intrauterine growth nad detect risks of neonatal and obstetric complications
each parameter is expected to follow a centile - showing steady increases in size
what do you need to ensure when taking measurements
that they are consistant - so make sure all the views are the same
for BPD and HC - make sure in midline, see the cavum and posterior horn of the lateral ventricles
for AC - transverse view of spine, stomach bubble and intrahepatic vein 1/3 from end of abdomen
what are the maternal factors that effect fetal growth *
poverty - malnutrition
age - very young and old, old have increased risk of placental disruption
drug use
weight
disease - hypertension, dm, coagulopathy
smoking and nicotine
alcohol
diet
prenatal depression
environmental toxins
feto-placental factors influencing fetal growth *
genotype-genetic potential
gender (B>G)
hormones
previous pregnancy
what are the fetal hormones that can effect growth *
pit - somatotrophin (via hepatic GF), FSH/LH (via gonadal steroid production)
panc - insulin
adrenal - androgens
gonads - androgens
thyroid - iodothyronines (probably by 3rd trimester)
describe the customised growth chart *
defines the individual fetal growth by:
- adjusting to reflect maternal constituitional variation eg height, weight, ethnicity, parity
- optimising by presenting a standard free from pathological factors eg smoking/dm
- is based on fetal weight curves defined by normal pregnancies
what is neonatal hydrocephalus
water in the brain
what is teh function of obstetric US examination *
assessment of fetal wellness - not just size ie is it moving, what amniotic fluid is like and the growth measurements
look at trends in growth - have a gap of 10days-2wks to see if they fall off centiles
predicting metabolic comprimise - if becoming growth restricted they will stop moving and direct blood to the major organs
anticipating the need to deliver prematurely
liasing with neonatal services
why has the use of data from miscarriages (historical data) been superseded *
didnt take accout of the possible causitive relationship between low fetak growth leading to miscarriage so data may be inaccurate
difference between fetal growth and fetal weight *
weight increases during pregnancy, growth levels off
describe how poverty affects fetal growth *
more likely to have chiuldren at a younger age = low birth weight
may have little education of risks of smoking. alcohol, drugs etc
more likely to have diseases that are harmful to the fetus
how does mother’s age effect fetal growth *
between 16-35 have healthier env for fetus than the extremities - have fewer complications
extremities have a higher risk of preterm labour, this increases for women in poverty, afirican-americans and people who smoke
younger - more likely to drink/smoke/illegal drugs
premature babies from young mothers are more likely to have neurological defects that will influecnce their coping capabilities, irritability, trouble sleeping, constant crying
increased risk of Downs when>40
young and older are more exposed to the rsiks of miscarriage, premature births and birth defects
women over 35 more likely to have linger labour -result in the death of the mother/fetus
describe how drug use effects fetal growth *
drugs are metabolised in the placenta and then go to the fetus - can cause addiction in babies
may lead to extreme irritability, crying and risk of SIDS
when using narcotics - greater risk of birth defects, LBW, and higher rate of death in infants/stillborn
marijuana - slow fetal growth rate and = premature delivery, can also lead to low birth weight, shortened gestational period and complications with the delivery
heroin - premature delivery, higher risk of miscarriages, facial abnormalities and head size and GI abnormalities, increased risk of SIDS, dysfunction of CNS and siezures, low birth weight, resp problems
cocaine = smaller brain= learning disabilities, stillborn/premature, LBW, damage to the CNS and motor dysfunction
effect of alcohol on fetal growth *
disruptions of the fetuses brain development and organisation adn affects maturation of the CNS
can lead to ehart defects, small brain - affect learning behaviours
cause behavioural problems, mental reatrdation and facial abnormalities - smaller eyes, thin upper lip and groove between nose and lip
increase risk of stillbirths and miscarriages or LBW
fetal alcohol syndrome - developmental disorder
effect of smoking/nicotine on fetal growth *
baby exposed to nicotine, tar and co
nicotine = less blood flow to the fetus - constricts the bv
co reduces ox flow to fetus
= stillbirth, LBW and ectopic pregnancy
increase in SIDS
increase risk of miscarriages, premature births, or infant mortality
link from smoking in pregnancy that led to asthma in childhood
effect of maternal diseases on fetal growth *
if mother effected with disease - placenta cant always filter out pathogens
babies can be born with venereal diseases transmitted by the mother
effect of mother;s diet and physical health on prenatal growth *
lack of iron = anaemia
lack of ca = poor bone and teeth formation
lact of protein can lead to smaller fetus and mental retardation
describe how mother’s prenatal depression affects growth *
associated with lower fetal growth rates - mother’s prenatal cortisol levels play a role
effect of environmental toxins on fetal growth *
exposure to environmental toxins leds to a higher rate of miscarriage, sterility and birth dgfects
including lead, mercury, ethanol or haszardous environments
how does fetal gender effect growth *
male babies are bigger than females
infants are generally heavier in subsequence pregnancies
effect of feto-placental hormones on fetal growth *
act on growth adn differentiation and enable a precise and orderly pattern of growth
actions may be mediated by other GR eg insulin like GFs - insulin stim growth by increasing the mitotic drive and nutrient availability for tissue growth
cortisol involved in maturation and differnetiation - acts directly on cells to alter gene transcription or-post translational processing of gene products, initiate switch form fetal to adult growth regulation ie IGF2-IGF1
thyroxine affects growth and maturation
GH not involved- showing growth in utero is due to changed metabolism and gene expression - to ensure rate is in line with nutrients and that intrauterine growth happens
insulin like growth factors are mitogenic - stimulate the fetal metabiolism and coordinating the feto-placental metabolism - IGF2 regulates early embryonic development, IGF1 is responsible for growth of the newborn
fetal insulin modulates expression if IGF, and has direct effects on the adipose tissue jad proliferation of the cells in the fetus; little effect on differentation
fetal glucocorticoid affects tissue differentiation and development of organs - lungs (surfactant), liver (control of glycaemia), intestines (maturation if the expression of digestive enzymes and proloferation of villi)
glucocorticoid with thyroid gland hormones affect development of CNS
use of US to determine fetal well being *
1st scan between 11 and 14wks
- confirm pregnancy is not ectopic
- confirm viability by location of heart beat
- number of fetuses
- assessment of gestational age by CR length
- measurement of nuchal translucency
- look for anencephaly, holoprosencephaly and major abdo wall defects
2nd between 18-20 wks
- confirm viability
- number of fetuses
- fetal biometry - head and abdomical circumferences, biparital diameter and femer length
- assessment of amniotic fluid vol
- assessment of placental location and cord insertion
- offering an anatomical survey to look for normal appearance in organ systems
why is US the preferred method for assessment of fetal growth *
it doesnt use radiation - so no harm to baby or mum
