Small for Dates Pregnancy and Pre-Term Birth

Question 1

Reasons for which a baby is small?

Answer 1

1. Preterm delivery
2. 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

Question 2

Major difference between preterm births and small for gestational age?

Answer 2

Preterm births tend to be proportionately small, for their gestation

Small for gestational age babies are disproportionately small

Question 3

Define preterm birth?

Answer 3

Delivery between 24 and 36+6 weeks

Question 4

Occurrence of preterm birth?

Answer 4

Prevalence is 6-7%

Question 5

Survival rate of preterm births?

Answer 5

If born at 24 weeks gestation - 50%

If born at 27 weeks gestation - 80%

If born at 32 weeks gestation - >95%

Question 6

Aetiology of preterm birth?

Answer 6

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

Question 7

Risk factors for preterm birth?

Answer 7

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)

Question 8

Situations where preterm births occur?

Answer 8

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

Question 9

Define Small for Gestational Age (SGA)

Answer 9

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

Question 10

Causes of IUGR?

Answer 10

Poor growth:
• Maternal factors
• Foetal factors
• Placental factors

Question 11

Maternal factors for IUGR?

Answer 11

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)

Question 12

Foetal factors for IUGR?

Answer 12

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

Question 13

Placental factor for IUGR?

Answer 13

Infarcts

Placental abruption -placental lining separates from the uterus of the mother, prior to delivery

Often secondary to hypertension

Question 14

Classifications of IUGR?

Answer 14

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

Question 15

Consequences of being growth restricted?

Answer 15

Antenatal / in labour - risk of hypoxia and/or death

Post-natal:
• Hypoglycaemia
• Effects of asphyxia
• Hypothermia
• Polycythaemia
• Hyperbilirubinaemia (jaundice)
• Abnormal neurodevelopment

Question 16

Clinical features of poor growth?

Answer 16

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

Question 17

Methods of assessing foetal wellbeing?

Answer 17

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

Question 18

What are acceleration in foetal heart rate?

Answer 18

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

Question 19

What is a loss of baseline variability?

Answer 19

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

Question 20

Why is a loss of baseline variability a problem?

Answer 20

Generally, the less baseline variability is present, the greater the possibility of asphyxia

Question 21

What are late decelerations?

Answer 21

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

Question 22

What was inv. with biophysical assessment?

Answer 22

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

Question 23

Methods of assessing foetal wellbeing?

Answer 23

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

Question 24

Purpose of MCA doppler?

Answer 24

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

Question 25

Purpose of ductus venosus doppler?

Answer 25

Reflects the myocardial contractility

Question 26

Main issues to consider with timing of delivering the baby?

Answer 26

If too early, can cause iatrogenic prematurity and assoc. issues

If too late, can cause perinatal asphyxia, cerebral palsy, IUFD, etc

Have to get the timing right