Small for Dates

Question 1

What can cause a baby to be small for its date?

Answer 1

• Pre term delivery
• Intra uterine growth restriction (IUGR)
• Constitutionally small

Question 2

A preterm birth is before what gestational age?

Answer 2

• Delivery before 37 weeks
• Extreme preterm: 24 – 27+6 weeks
• Very preterm: 28 – 31+6 weeks
• Moderate to late preterm: 32 – 36+6 weeks

Question 3

What is the difference in survival when babies are born very preterm?

Answer 3

23 weeks = 19%
Whereas
26 weeks = 77%

Question 4

What conditions may cause a preterm birth?

Answer 4

• Infection - Pyelonephritis / UTI/ Appendicitis/ Pneumonia
• ‘Over distension’ => Multiple Preg/Polyhydramnios
• Vascular => Placental abruption
• Cervical incompetence
• Idiopathic

Question 5

What factors increase the risk of a preterm birth?

Answer 5

• Previous pre-term labour
• Multiple
• Uterine anomalies
• Age (teenagers)
• Parity (=0 or >5)
• Ethnicity
• Poor socio-economic status
• Smoking
• Drugs (especially cocaine)
• Low BMI (<20)

Question 6

What can cause a pre-term labour?

Answer 6

• Planned caesarean section (pre-eclampsia, kidney disease or poor fetal development)
• Premature rupture of membranes
• Emergency (placental abruption, infection, eclampsia)
• Idiopathic

Question 7

What does it mean if a baby is defined as “Small for Gestational Age”?

Answer 7

Estimated foetal weight (EFW) or Abdominal Circumference below the 10th centile

Question 8

What is meant by the terms Intra-uterine growth restriction (IUGR) and low birth weight (LBW)?

Answer 8

IUGR = Failure to achieve growth potential

LBW = birth weight below 2.5 kg (regardless of gestation)

Question 9

Intra-uterine growth restriction can be symmetrical or asymmetrical. Explain what this means and what is most likely to cause each.

Answer 9

Symmetrical = all parts of baby’s body are proportionately small
- usually caused by chromosomal problem

Asymmetrical = head normal, but abdomen is small => disproportionate to each other
- usually caused by placental supply problems => foetus directs all blood to head to keep brain perfused

Question 10

Give some examples of major and minor antenatal risk factors for small babies?

Answer 10

MAJOR

• BMI>40
• Smoking >11 cigarettes /day
• Other medical conditions - HT, Diabetes, renal disease, antiphospholipid

MINOR

• Maternal age >35 years
• IVF
• Low BMI <20
• Smoker 1-10 cigarettes/day
• Low fruit pre-pregnancy

Question 11

How do we screen for small babies antenatally?

Answer 11

• Measurement of symphysial-fundal height from 24 weeks

- Growth scan if measurement below 10th centile on customised chart

Question 12

HOw can we diagnose a baby that is small for gestational age?

Answer 12

• Measurement of fetal abdominal circumference
• Combine with head circumference +/- femur length to give Estimated Foetal Weight (EFW)
• liquor volume or amniotic fluid index can also be used to see if baby is producing enough fluid

Question 13

How is EFW/AC Measurement standardised? WHat is seen on every womans scan to calculate this?

Answer 13

Scan till we can see:

• stomach gas bubble
• C shaped umbilical vein
• One rib

ALL in the same snapshot on US

Question 14

What do customised charts take into account that population charts do not?

Answer 14

• BMI
• Parity of mother
• Ethnicity

Question 15

What maternal factors can cause a baby to be Small for gestational age (SGA)?

Answer 15

• Lifestyle (smoking, alcohol, drugs)
• Height and weight
• Age
• Maternal disease e.g. hypertension

Question 16

What are uterine artery dopplers used to measure?

Answer 16

Resistance in uterine arteries
- “notch” indicates high resistance in vessels
=> harder for blood to reach baby
=> harder for baby to grow

Question 17

What placental factors can cause a baby to be small for their gestational age?

Answer 17

• Infarcts
• Abruption

Often secondary to hypertension

Question 18

What are the potential foetal causes of a baby being small for their gestation?

Answer 18

• Infection e.g. rubella, CMV, toxoplasma
• Congenital anomalies e.g. absent kidneys
• Chromosomal abnormalities e.g. Down’s syndrome

Question 19

What are the consequences of IUGR antenatally or when the mother is in labour?

Answer 19

• hypoxia and or death

Question 20

What are the consequences of IUGR postnatally for the baby?

Answer 20

• Hypoglycaemia
• Effects of asphyxia
• Hypothermia
• Polycythaemia
• Hyperbilirubinaemia
• Abnormal neurodevelopment

Question 21

HOw may poor growth be suspected clinically?

Answer 21

• Predisposing factors
• Fundal height less than expected
• Reduced liquor
• Reduced fetal movements

Question 22

What does a biophysical profile include to assess growth of the foetus?

Answer 22

US assessment that considers:
- Movement
- Tone
- Foetal breathing movements
- Liquor volume
Scores out of 10 (8-10 satisfactory)

Question 23

What is an umbilical artery doppler used for?

Answer 23

Checks placental resistance to blood flow to foetus

• when mother is in diastole, blood flow to foetus falls
• it should NOT stop during diastole
• if resistance is extremely high, blood may flow BACK to the mother (Opposite direction) during diastole

Question 24

When may a small baby be delivered early by c-section?

Answer 24

• Growth becomes static (induce labour?)
• Abnormal umbilical artery Doppler
• Abnormal MCA between 32 and 37 weeks
• Abnormal umbilical artery Doppler with abnormal ductus venosus Doppler between 24-32 weeks

Question 25

What medication should be given to the mother if planning delivery?

Answer 25

Steroids

Magnesium sulphate

Question 26

Why may it be appropriate to NOT deliver a small for gestational age baby at 37 weeks (as per guidelines) if both the baby and mother are well?

Answer 26

Closer to 40 weeks = less potential for educational difficulty in later life