Pregnancy - small for dates

Question 1

What are the 2 primary causes of a small baby ?

Answer 1

1. Pre-term birth (so normal for their gestation, its just that they are young)
2. Small for gestational age (SGA)

Question 2

Define what pre-term delivery is and the 3 sub-classifications of it

Answer 2

Defined as delivery between 24 & 36+6 weeks:

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

Question 3

What happens to the survival rate of pre-term pregnancies as they decrease in prematurity i.e. get older

Answer 3

• Survival rate increases the less premature they are
• Beyond 32 weeks >95% survival

Question 4

List the causes of pre-term delivery

Answer 4

• Infection
• ‘Over distension’; Multiple pregnancy, polyhyraminos
• Vascular; Placental abruption
• Intercurrent illness; Pyelonephritis / UTI, Appendicitis, Pneumonia
• Cervical incompetence - cervix dilates before pregnancy has reached term
• Idiopathic (unknown)

Question 5

List the risk factors for pre-term birth and highlight the 2 main ones to know about

Answer 5

• Previous Pre-term labour (20% risk X1; 40% X2))
• Multiple (50% risk)
• Uterine anomalies
• Age (teenagers)
• Parity (=0 or >5)
• Ethnicity
• Poor socio-economic status
• Smoking
• Drugs (especially cocaine)
• Low BMI (<20)

Question 6

what are the 4 main ways pre-term labour presents ?

Answer 6

• 25% planned caesarean section - Severe pre-eclampsia, kidney disease or poor fetal development.
• 20% premature rupture of membranes (PROM)
• 25% emergency event - Placental abruption, infection, eclampsia
• 40% cause unknown

Question 7

What are the symptoms suggestive of pre-term labour ?

Answer 7

• Contractions
• Rupture of membranes (can happen a fair bit before labour starts)
• Brownish or blood tinged mucus discharge

Question 8

How is PROM diagnosed ?

Answer 8

• 1st line = Speculum exammination - if amniotic fluid pooling seen offer management, if none seen then:
• 2nd line = Consider performing insulin like growth factor binding protein-1 test or placental alpha-microglobulin test of vaginal fluid

If both +ve then give antibiotics, if only insulin or placental alpha test +ve then consider their clinical condition & if neither +ve then reassure PROM is unlikely

Question 9

If PROM suspected and labour has already been established, should you carry out the diagnostic tests for PROM?

Answer 9

No

Question 10

What is the management of PROM?

Answer 10

• 80% of PROM will initiate labour but in 20% it will not & may take a while before labour starts
• If labour has initiated then management is that of pre-term labour
• If labour does not initiate then there is now a risk of developing infection (due to ceale being broken) ==> antibiotics are given

Question 11

What antibiotics are given for PROM when labour has not initiated ?

Answer 11

• 1st line = erythromycin (max 10 days until labour established)
• 2nd line = penicillin (if erythro not tolerated)

Question 12

What is the management options for cervical incompentence ?

Answer 12

• For women between 16 to 27+6 weeks with a dilated & exposed, unruptured fetal membranes a rescue cervical cerclage (cervical stitch) can be done
• Contraindicated if signs of infection, active vaginal bleeding or uterine contractions

Question 13

Does initiations of contractions always lead to pre-term labour ?

Answer 13

No - in 50% of cases contractions cease spontaneously & treating the cause e.g. pylonephritis may make it cease

Question 14

What is the management of pre-term labour ?

Answer 14

Treat underlying cause if possible e.g. pylonephritis and it may cease

Give glucocortiocosteroids - for all at risk of iatrogenic or spontaneous pre-term birth between 24 & 34+6 weeks and consider for suspected or established pre-term labour, those having elective pre-term birth or who have prelabour PROM between 24 & 35+6 weeks (note need roughly 24hrs to work prior to the actual delivery)

Tocolytics (anti-contraction drugs) - for pregnancy with intact membranes & are in suspected or diagnosed preterm labour:

• 1st line = nifedipine
• 2nd line = oxytocin receptor antagnosit e.g. atosiban if nifedipine contraindicated

IV Magnesium sulphate (MgSO4) - for neuroptoection of baby when in established pre-term labour or having a planned one within 24hrs between 24 & 33+6 weeks

Question 15

When is use of nifedipine contraindicated for pre-term labour ?

Answer 15

If the women has heart disease

Question 16

What are the side effects of nifedipine ?

Answer 16

• Decreased BP
• Facial flushing
• Headache
• Increased pulse
• Very rarley MI

Question 17

Why is it important to differentiate between babies who are premature and those who are SGA, why?

Answer 17

Because they are at risk for different problems following birth

Question 18

What are the 2 causes of a baby being small for their gestational age (SGA)?

Answer 18

1. Intra-uterine growth restriction (IUGR) - this is pathological
2. Baby is constitutinally small (familial)

Question 19

Define what small for gestational age (SGA) is

Answer 19

This is an infant with a birthweight that is less than the 10th centile for their gestation when compared to general population & customised growth charts (corrected for maternal height, weight, fetal sex & birth order)

Question 20

Define what low birth weight is

Answer 20

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

Question 21

What can IUGR broadly speaking be due to problems with what 3 main things ?

Answer 21

1. Maternal
2. Fetal
3. Placental

Question 22

What maternal factors can lead to IUGR ?

Answer 22

• Lifestyle; Smoking, Alcohol, Drugs
• Height and weight - BMI < 20
• Age ≥ 40
• Maternal disease e.g. HTN, renal impairment, DM, PET

Question 23

What fetal factors can lead to IUGR ?

Answer 23

• Infection e.g. Rubella, CMV, toxoplasma
• Congenital anomalies e.g. absent kidneys
• Chromosomal abnormalities e.g. Downs syndrome

Question 24

What placental factors can lead to IUGR ?

Answer 24

• Infarcts
• Abruption
• Often secondary to HTN

Question 25

IUGR implies a pathological restriction of the genetic growth potential of a fetus, as a result IUGR fetuses may manifest evidence of fetal compromise which may be indicated by what?

Answer 25

* Abnormal doppler studies * Decreased liquor volume

Question 26

What are the potential consequences of IUGR ?

Answer 26

* Antenatally/ in labour - risk of hypoxia &/or death Postnatally: * Hypoglycaemia * Effects of asphyxia * Hypothermia * Polycythaemia * Hyperbilirubinaemia * Abnormal neurodevelopment

Question 27

What are the clinical features suggestive of IUGR ?

Answer 27

* Predisposing factors * SFH \< than expected * Reduced liquor (oligohyraminos) * Reduced fetal movements

Question 28

What is done to assess fetal wellbeing (survellience of a SGA baby)?

Answer 28

* **Assessment of growth** * **CTG** * **Doppler US** Biophysical profile (now not done)

Question 29

How is the growth of a fetus assessed ?

Answer 29

* Initially use SFH and plot measurements against centile charts at each antenatal appointement from 24 weeks * If growth restriction suspected (AC or EFW below the 10th centile) then monitor growth with serial U/S of head & abdominal circumference

Question 30

How is a CTG assessed in the assessment of a SGA ?

Answer 30

DR C BRAVADO - covered in another lecture

Question 31

Serial growth scans and CTG are used in the assessment of a SGA baby but what is the primary survellience tool?

Answer 31

Umbilical artery doppler (middle cerebral artery doppler & ductus venous suppler also used) - it is used to measure placental resistance to blood flow

Question 32

Go over these points on US assessment of a SGA baby

Answer 32

* Umbilical artery should be low resistance but if compromised becomes high resistance, so flow becomes absent or even reversed in diastole. * Ductus venosus becomes pulsatile and increases its resistance. * Middle cerebral artey decreases its resistence to maintain blood flow to fetal brain.

Question 33

When should a SGA baby be delivered ?

Answer 33

**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 Note - Delivery of the SGA infant is a balance between the risks of prematurity and the potential of hypoxia in utero or still birth.