Small for Dates Pregnancy and Pre-Term Birth Flashcards
(26 cards)
Reasons for which a baby is small?
- Preterm delivery
- Small for gestational age:
• Intra-Uterine Growth Restriction (IUGR) - placenta is not working well; can lead to disabilities and, if extreme, to intra-uterine foetal death (IUFD)
• Constitutionally small - child is small but healthy
Major difference between preterm births and small for gestational age?
Preterm births tend to be proportionately small, for their gestation
Small for gestational age babies are disproportionately small
Define preterm birth?
Delivery between 24 and 36+6 weeks
Occurrence of preterm birth?
Prevalence is 6-7%
Survival rate of preterm births?
If born at 24 weeks gestation - 50%
If born at 27 weeks gestation - 80%
If born at 32 weeks gestation - >95%
Aetiology of preterm birth?
Idiopathic (most common cause)
Infection - usually a systemic illness, e.g: pyelonephritis
Over-distension of the uterus can be caused by:
• Multiple, e.g: twins
• Polyhydramnios
Vascular:
• Placental abruption
Intercurrent illness:
• Pyelonephritis / UTI
• Appendicitis
• Pneumonia
Cervical insufficiency - cervix begins to dilate and efface before the pregnancy has reached term
Risk factors for preterm birth?
Previous preterm labour (PTL) - BIGGEST RISK FACTOR
Multiple (50% risk of preterm birth)
Uterine anomalies
Age (extremes of maternal age)
Parity (if it =0 or >5)
Ethnicity
Poor SE status
Smoking
Drugs, esp. cocaine
Low BMI (<15)
Situations where preterm births occur?
40% cause unknown
25% planned caesarian section due to e.g:
• Severe pre-eclampsia
• Kidney disease
• Poor foetal development
20% premature rupture of membranes
25% are in emergency events:
• Placental abruption
• Infection
• Eclampsia
Define Small for Gestational Age (SGA)
Infant with a birthweight that is less than 10TH CENTILE for their gestation, corrected for maternal height, weight, foetal sex and birth order
If baby is <10th centile:
• 50% due to IUGR
• 50% are constitutionally small
NOTE - these must be differentiated
Causes of IUGR?
Poor growth:
• Maternal factors
• Foetal factors
• Placental factors
Maternal factors for IUGR?
Lifestyle:
• Smoking
• Alcohol (causing foetal alcohol syndrome)
• Drugs, esp. cocaine (vasoconstrictor, so it affects blood flow in the placenta)
Height and weight of mother (low BMI and a very high BMI)
Age, esp. advanced maternal age
Maternal disease, e.g:
• Hypertension
• Diabetes (typically results in macrosomia, however vascular damage to the placenta could lead to IUGR)
Foetal factors for IUGR?
CHROMOSOMAL ABNORMALITIES, e.g: Down’s syndrome, esp. if other signs like an umbilical hernia, AV septal defect, etc
Infection, e.g: Rubella, CMV, toxoplasma
Congenital anomalies, e.g: absent kidneys
Placental factor for IUGR?
Infarcts
Placental abruption -placental lining separates from the uterus of the mother, prior to delivery
Often secondary to hypertension
Classifications of IUGR?
Symmetrical - small head AND small abdomen; this is usually caused by early-onset IUGR, typically due to a chromosomal abnormality
Asymmetrical - normal head and small abdomen; this is usually caused by late-onset IUGR
Consequences of being growth restricted?
Antenatal / in labour - risk of hypoxia and/or death
Post-natal: • Hypoglycaemia • Effects of asphyxia • Hypothermia • Polycythaemia • Hyperbilirubinaemia (jaundice) • Abnormal neurodevelopment
Clinical features of poor growth?
Predisposing factors
Fundal height (less than expected)
Reduced liquor
Reduced foetal movements - if this occurs in a small foetus, worried about hypoxia
NOTE - if reduced FM is for a short period of time, may be due to the foetus being asleep; however, it should be assessed
Methods of assessing foetal wellbeing?
Assessment of growth, inc. baby’s head and abdominal circumferences
Cardiotocography (CTG) - measure foetal heartbeat and uterine contractions
Biophysical assessment (not used anymore)
Doppler USS
What are acceleration in foetal heart rate?
Increased in foetal HR at the start of a uterine contraction, returning to the baseline rate before or sometime after the uterine contraction
Indicative of good reflex reactivity of the foetal circulation
What is a loss of baseline variability?
A baseline foetal HR variability of <5 bpm (this should normally be 5-15 bpm)
Can be caused by sedative/analgesic drugs used during labour, e.g: morphine; if it only occurs for short periods, may be due to the foetus being asleep
Why is a loss of baseline variability a problem?
Generally, the less baseline variability is present, the greater the possibility of asphyxia
What are late decelerations?
Any deceleration in HR, whose lowest point is past the peak of the contraction, i.e: decelerations with ‘lag-time’
These types of deceleration are usually assoc. placental insufficiency and asphyxia; generally, the longer the ‘lag-time’, the more serious the foetal asphyxia
What was inv. with biophysical assessment?
No longer done but included:
• USS - movement, tone, foetal breathing movements, liquor volume
Scored out of 10:
• 8-10 is satisfactory
• 4-6 means a repeat should be done
• 0-2 means the baby should be delivered
Methods of assessing foetal wellbeing?
Umbilical arterial Doppler - should look like a toblerone, with lots of chocolate between the peaks; sometimes:
• Absent end-diastolic flow - sign of placental insufficiency
• Reversed end-diastolic flow - sign that a caesarian section is urgently required
Uses USS
Measured placental resistance to flow
Purpose of MCA doppler?
If foetus has anaemia, hypoxia, placental issues, etc, the blood flow to the brain, and thus in the MCA, increases to protect the foetal brain; this can be seen on MCA doppler
