Tutorial 7: SGA and Reduced Fetal Movements

Question 1

What is SGA?

Answer 1

birthweight <10th centile for gestational age. i.e. 2 standard deviations below mean weight for GA (below 10th percentile).

2x types: symmetrical (20-30%) and asymmetrical (70-80%) SGA

Question 2

What is the difference between SGA and IUGR?

Answer 2

IUGR: failure to obtain growth potential in utero

SGA DOES NOT equal IUGR, ie. A constitutionally small baby is SGA but not IUGR.

“Failure to reach growth potential” is difficult to measure and define, therefore SGA is often used as a surogate for IUGR.

Question 3

What are features of Symmetrical SGA?

Answer 3

Symmetrical: 20-30%

• All fetal measurements are low
• Intrinsic fetal insults occur EARLY in pregnancy and affect fetal growth at a time of development when cell division is the predominant mechanism of growth
• Types of Intrinsice Fetal insults:
  
  • 1. Infection
  • 2. Chromosomal abnormalities
  • 3. Congenital malformations
  • 4. Drugs
• Greater morbidity and mortality outcomes

Question 4

What are features of asymmetrical SGA?

Answer 4

• Abdominal circumference is disproportionately low compared with the head circumference (HC = HL >Wt)
  
  • head circ = height but > weight
• Extrinsic insult occurring LATER in pregnancy. Usually characterized by inadequate fetal nutrition due to placental insufficiency.
• Causes of extrinsic fetal insults: Maternal hypertension, placental insufficiency
• Lower morbidity and mortality outcomes

Question 5

Why do we use customized fetal growth charts for best practice?

Answer 5

They are growth charts which take into account maternal variables known to affect birth weight – maternal height, booking weight, parity and ethnicity.

A customized growth chart allows for better distinction between normal and abnormal smallness.

These charts have a higher detection rate than standard ultrasound growth charts for poor fetal growth.

Question 6

What do fetal growth charts show?

Answer 6

2x types of fetal growth charts: population and customised

Symphysis fundal height (SFH) is plotted serially and if an USS is performed, estimated fetal weight is also plotted.

Use of customized growth charts has been shown to increase antenatal detection of SGA babies.

This can be indicated when growth crosses centiles or is below the 10th percentile = needs a growth scan.

Question 7

What is the correct way to assess fundal height?

Answer 7

• Ask woman to empty bladder prior to examination
• Palpate for fundus of uterus with both hands from the xiphisternum and secure non-elastic tape at 0cm with hand
• Bring tape down along longitudinal axis of uterus to upper edge of pubic symphysis and read in centimetres

Question 8

What factors can impact their fundal height measurement?

Answer 8

Shorter measure due to:

• fetus descent into pelvis (2-4 weeks beforedelivery)
• SGA
• oligohydramnios
• fetus positioned sideways (transverse lie)

Longer measure due to:

• multiple preg
• LGA
• gestational diabetes,
• polyhydramnios
• breech

SFH may be unreliable in women with booking weight over 100kg

Question 9

What 4x USS measurements do you use to assess fetal growth?

Answer 9

1. Abdominal circumference
2. Head circumference
3. Biparietal diameter (BPD)
4. Femur length

The above 4 measurements can be used to provide a composite age estimate.

Question 10

What are common causes of SGA?

Answer 10

1. Incorrectly dated pregnancy
2. Constitutionally small
3. IUGR
   
   • Non-placenta mediated growth restriction
   • Placenta mediated growth restriction
   • Maternal factors

Question 11

What are common causes of IUGR?

Answer 11

Non-placenta mediated growth restriction/fetal

• Chromosomal abnormality
• Congenital abnormality
• Inborn errors of metabolism
• Fetal infection

Placenta mediated growth restriction

• Small placenta
• Placental abruption
• Placenta previa
• Placental infarcts

Maternal factors

• Low pre-pregnancy weight
• Malnutrition
• Substance abuse
• Severe anaemia
• HTN – essential, preeclampsia
• Autoimmune disease
• Thrombophilias
• Renal disease
• Diabetes
• Smoking

Question 12

What is the significance of SGA during pregnancy?

Answer 12

INCREASED RISK OF PERINATAL MORBIDITY AND MORTALITY - but most adverse outcomes are concentrated in the IUGR group.

Perinatal:

• Intrauterine death
• Poor temperature regulation/hypothermia
• Low resistance to infection
• Hypoxia in labour and at delivery
• Early hypoglycaemia
• Feeding problems
• Jaundice

Question 13

What is the significance of SGA longterm, both during childhood and adulthood?

Answer 13

Long term – paediatric/childhood

• Short stature
• Neurodevelopmental impairment
• Cerebral palsy

Long term - adult

• HTN
• Diabetes
• CVD

Question 14

What advice should you give re smoking in early pregnancy?

Answer 14

Smoking is the single most avoidable cause of SGA babies.

There is a Smokefree Pregnancy Service which is free for you and your partner and can help support you to quit smoking.

They can help you to make a quit plan and can provide you with patches, gum and lozenges.

Use of NRTs nicotine replacement therapies in pregnancy is still safer than smoking.

Question 15

What antenatal monitoring should occur once the baby is identified as SGA?

Answer 15

1. Reduce maternal risk factors – monitor BP, smoking cessation, blood sugar control
2. Fetal surveillance – as there are no current treatments for SGA, optimal management aims to achieve delivery of the infant in the best possible condition, balancing the risks of prematurity against the risks of the in-utero environment. The goal of surveillance in the SGA pregnancy is therefore to identify the fetus at risk of intrauterine acidaemia and death.

Weekly clinical checks and fortnightly growth scan, AFI and UAD. Frequency of monitoring may be increased depending on severity:

Question 16

What does Fetal Surveillance involver?

Answer 16

1. Fetal movement monitoring – reduced fetal movements (RFM) often precede fetal death. Although there is no evidence to support keeping formal kick charts, it is recommended that all women with known SGA fetuses are advised to report any change in their normal fetal movement patterns
2. Growth scan
3. Amniotic fluid assessment – low amniotic fluid is associated with increased perinatal morbidity. Abnormal is <5cm
4. Umbilical artery Doppler – primary tool of surveillance for SGA. During normal pregnancy, resistance in the umbilical circulation falls and blood flow velocities increase with advancing gestation. Abnormal umbilical Doppler waveforms, esp absent or reversed-end diastolic velocity, are associated with major placental abnormalities. Doppler flow indices expressed as resistance index (RI)

• ​Abnormal RI
  
  • ​RI > 0.80 @26 wks
  • RI >0.75 @ 32 wks
  • RI >0.70 @37 wks

Question 17

What intrapartum monitoring occurs (during labour) for a known SGA baby?

Answer 17

Continuous CTG monitoring is recommended. If there is any indication of deteriorating fetal status, then LSCS.

See above figure for delivery timing +/- steroids. Vaginal birth should be encouraged unless absent or reversed-end diastolic velocity present, then LSCS.

Question 18

What are the general recommendations re maternal monitoring of fetal movements during pregnancy?

Answer 18

• Women should be advised to be aware of their baby’s individual pattern of movements. If they are concerned about a reduction in or cessation of fetal movements after 28 weeks gestation, they should contact their maternity unit
• If women are unsure whether movements are reduced after 28 weeks gestation, they should lie still and focus on fetal movements for 2 hours. If they do not feel 10 or more discrete movements in 2 hours, they should contact their midwife or maternity unit immediately

Question 19

What Risk Factors should be questioned for during the “booking visit” for SGA baby?

Answer 19

Maternal Risk Factors:

1. age
2. parity
3. BMI
4. Maternal substance exposure
5. IVF
6. Exercise
7. Diet

Previous pregnancy History:

1. Previous SGA
2. PRevious Stillbirth
3. Pervious Pre-eclampsia
4. Pregnancy Interval

Maternal Medical history:

1. SGA
2. HT
3. DM
4. Renal disease
5. APLS

Paternal Medical history: SGA

Question 20

OSCE Station:

Basically had to read a growth chart and explain to the mother what is happening with the growth of the baby and what can be causing the fetus to be small. Also we got asked to predict the birth weight. Keep in mind that some babies cross centiles but then keep growing along the new curve.

Answer 20

SGA – 2 standard deviations below mean weight for GA – below 10th percentile.

SGA Causes:

• Hypertension
• Pre-eclampsia
• Smoking
• TORCH infections
• Chromosomal/congenital abnormalities
• Constitutionally small patients eg. Indians.

SGA DOES NOT equal IUGR, ie. A constitutionally small baby is SGA but not IUGR. AGA – between 10th and 90th percentile

LGA – above 90th percentile. Causes:

• Diabetic mother
• Constitutionally large
• Patients eg. Maori/Pacific, hydrops fetalis, Beckwith-Wiedemann

IUGR – failure of normal fetal growth caused by multiple adverse effects on the fetus. Incidence 3-10%. Associated with 4-8x higher perinatal mortality and results in serious morbidity in 50%. Barker’s hypothesis.

IUGR can be symmetrical or asymmetrical.

Symmetrical: HC=Ht=Wt and are all under 10th percentile. Can be due to infection or genetic disorder.

Asymmetrical: HC=Ht>Wt and are all under 10th percentile. For example, the fetal weight may be under 2nd percentile, disproportionally reduced. Can be due to uteroplacental insufficiency, maternal malnutrition.