Small for Dates Flashcards
why might a baby be small
pre term delivery
small for gestational age:
- IU/ fetal growth restriction
-constitutionally small
what are the categories of pre term births
pre term= before 37 weeks moderate to late preterm= 32-36+6 very pre term= 28-31+6 extreme preterm= 24-27+6 (can have babies surviving 23 weeks, earliest ever is 21)
at what pre term date is survival >95% (same as term)
beyond 32 weeks
why is pre term birth important
survival and long term outcome worse the earlier the baby is born
why might a baby be born pre term
infection
over distention - multiple pregnancies, polyhydramnios
placental abruption
intercurrent illness- polynephritis/ UTI, appendicitis, pneumonia
cervical incompetence
idiopathic
what are the risk factors for pre term birth
previous PTL (20%-40%) multiple pregnancies (505) uterine abnormalities age (teenagers) parity (=0 or >5) ethnicity poor socio-economic status smoking drugs (esp cocaine) low BMI (<20)
what are the most common reasons for preterm birth
25% planned CS- severe pre eclampsia, kidney disease or poor fetal development
20% premature rupture of membranes
25% emergency - placental abruption, infection, eclampsia
40% unknown
what classifies as small for gestation age
EFW/ AB below the 10th centile (population or customised centiles)
define IUGR/ fetal growth restriction
failure to achieve growth potential
what classifies low birth weight
birth weight below 2.4kg regardless of gestation
what paths on growth centiles will IUGR and constitutionally small babies follow
IUGR will drop off centiles
constitutionally small babies will grow along lower centiles
what are the types of growth restrictions
symmetrical= small head and body= chromosomal abnormality/ in utero infection / environmental
asymmetrical= normal head and small body= suggests placental reasons- e,g, baby diverting blood to head over less vital organs = PET, placental causes, smoking
what are the minor risk factors for a SGA (Small gestational age) baby
Maternal age >35 years IVF pregnancy Nulliparity BMI <20 BMI 25-34.9 Smoker 1-10 cigarettes/day Low fruit pre-pregnancy Previous pre-eclampsia Pregnancy interval <6 months Pregnancy interval >60 months
what are the major risk factors for a SGA baby
Maternal age >40 years Smoker >11 cigarettes/day Paternal SGA Cocaine use Daily vigorous exercise Previous SGA baby Previous stillbirth Maternal SGA Chronic hypertension Diabetes with vascular disease Renal impairment Antiphospholipid syndrome Heavy bleeding in pregnancy Low PAPP-A Fetal echogenic bowel BMI >35 Known large fibroids
how do you identify SGA babies
maternal risk factors (1 major = USS’s from 26-28 weeks until 36 weeks= serial growth scans) (3 minor= growth scan at 34 weeks and if abnormal uterine doppler artery measurement at 20 weeks then monitored as if they had major risk factor)
antenatal screening
when do all women get a symphysial fundal height taken
24 weeks
what should you do if SFH below 10th centile
growth scan
what do 2 or 3 SFH measurements that suggest slow of static growth require
a growth scan
how do you diagnose SGA
measurement of fetal AC
combine with
head circumference +/- femur length
to get EFW
also use liquor volume or amniotic fluid index and dopplers
what does liqour volume/ amniotic fluid index show in SGA
fluid around baby if normal suggests a healthy baby, if low suggests a sick baby and in the context of SGA may make you more suspicous that this baby is sick rather than constitutionally small
what do doppler scans show
the blood flow to baby through the placenta and also how the baby is managing that blood flow within their own circulation
what should be seen when measuring AC
stomach bubble
single rib
C shaped umbilical vein
what are the three divisions for SGA causes
maternal
fetal
placental
what maternal factors can cause SGA
Lifestyle: Smoking Alcohol Drugs Height and weight Age Maternal disease e.g. hypertension
what should uterine arteries be like in pregnancy
Pregnancy should be a low resistance state and the uterine arteries should become a low resistance vessel in the 2nd trimester with forward flow to the placenta even in diastole
what can happen if there is resistance in both uterine arteries
at risk of SGA and hyeprtensive disease in pregnancy and pre eclampsia
what usually causes resistance in the uterine arteries
abnormal placentation= so failure of the spiral artery invasion.
what are the placental causes of SGA
Infarcts
Abruption
Often secondary to hypertension
(placenta not functioning properly= growth restriction)
what are the fetal causes of SGA
infection- rubella, CMV, toxoplasma
congenital anomalies- absent kidneys
chromosomal abnormalities- downs syndrome
what do you screen for when SGA is suspected early on
downs syndrome
SGA early on likely to be fetal factors
what are the consequence of IUGR
Antenatal / in labour: risk of hypoxia and or death Post natal: Hypoglycaemia Effects of asphyxia Hypothermia Polycythaemia Hyperbilirubinaemia Abnormal neurodevelopment - cerebral palsy, developmental delay
what are the clinical features of poor growth
predisposing factors
low SFH
reduced liquor
reduced fetal movements (important to tell mothers this so they can monitor movements)
how do you asses fetal well being in SGA
assess growth (serial growth scans)
cardiotocography
biophysical assessment
doppler US
what is a biophysical profile
USS + CTG assessment that considers Movement Tone Fetal breathing movements Liquor volume
scores out of ten:
8-10 satisfactory; 4-6 repeat; 0-2 deliver
what does an umbilical arterial doppler measure
placental resistance to flow
pregnancy is a low resistance state and there should always be flow to the baby even in maternal diastole.
So a normal Doppler will show a constant flow of blood to baby even in diastole.
If there is developing resistance the Dopplers may deteriorate showing absent flow in diastole and the final step would be this flow becoming reversed so baby is not getting the nutrients they need from the placenta
what is the primary tool for monitoring SGA and timing delivery
umbilical arterial doppler
what can a MCA and Ductus Venosus Doppler show
if baby is diverting blood flow to its head to preserve vital functions at the expense of non vital organs
when should you deliver a SGA baby
If all well = deliver by 37 weeks
Indications for considering earlier delivery by caesarean section:
Growth becomes static (IOL may be appropriate)
Abnormal umbilical artery Doppler
Normal umbilical artery Doppler with abnormal MCA between 32 and 37 weeks
Abnormal umbilical artery Doppler with abnormal ductus venosus Doppler between 24-32 weeks
what drugs may be indicated if considering an earlier planned delivery
steroids- help lungs mature before 36 weeks
Magnesium sulphate which provides some fetal neuroprotection against cerbral palsy if delivery is planned before 32 weeks.
what do you have to balance when timing SGA birth
the risks of prematurity and the potential of hypoxia in utero or still birth
what is the role of the ductus venous in pregnancy
allow shunting of oxygenated blood to by pass the liver and move via IVC to oxygenate the brain.
which is oxygenated- the umbilical artery or vein
vein
