SGA/LGA

Question 1

Define ‘small for gestational age’

Answer 1

an infant with a birth weight <10th centile for its gestational age.

Severe SGA = birth weight < 3rd centile.

Question 2

What are fetal growth restrictions?

Answer 2

When a pathological process has restricted genetic growth potential.

This can present with features of fetal compromise including reduced liquor volume (LV) or abnormal doppler studies.

The likelihood of FGR is higher in a severe SGA fetus.

Question 3

What are the risk factors for SGA?

Answer 3

Minor =

• maternal age >35
• smoker 1-10/day
• nulliparity

Major =

• maternal age >40
• smoker >11/day
• previous SGA baby
• previous stillbirth
• cocaine use
• heavy bleeding
• maternal disease (HTN, renal impairment, DM)

BMI

Question 4

How is SGA investigated?

Answer 4

US = estimated fetal weight + abdo circumference are plotted on customised centile charts

These charts take into account maternal characteristics (height, weight, ethnicity and parity), gestational age and sex

Other =

• HC:AC
• Detailed fetal anatomical survey
• Uterine artery Doppler (UAD)
• Karyotyping
• screen for infections

Question 5

How should SGA be prevented?

Answer 5

Smoking cessation

Optimising maternal disease

High risk pre-eclampsia = 75mg aspirin

Question 6

Outline the surveillance of SGA

Answer 6

UAD - repeat every 14 days

Symphysis fundal height (SFH), middle cerebral artery (MCA) Doppler, ductus venosus (DV) Doppler, cardiotocography (CTG) and amniotic fluid volume

Question 7

What are the complications of SGA?

Answer 7

Neonatal = birth asphyxia, meconium aspiration, hypothermia, hypo/hyperglycaemia, polycythaemia, retinopathy, pulmonary HTN

Long-term = cerebral palsy, T2DM, obesity, HTN, precocious puberty, depression, Alzheimer’s disease, cancer

Question 8

How does SGA effect the timing and mode of delivery?

Answer 8

Umbilical A normal = delay delivery until 37w

AREDF (absent or reversed end diastolic flow) consider delivery if >34/40w

AREDF delivery before 34/40w if other doppler parameters abnormal

Question 9

How can fetal growth be assessed?

Answer 9

Abdo palpation of fundal height (sensitivity 20-30%)

Symphysis-fundal height measurement (sensitivity
30-40%)

US measurement (sensitivity 90-95%)

• Head circumference
• Abdo circumference
• Femur length

Question 10

What factors can make a fetus appear larger on clinical assessment?

Answer 10

Uterine fibroids

Ovarian tumour

Pelvic mass pushing up the uterus

Polyhydramnios

Maternal obesity

Question 11

What can cause a fetus to be large?

Answer 11

Maternal

• DM
• Obesity
• Increased maternal age
• Multiparity
• Large stature

Fetal

• Constitutionally
• Male gender
• Post maturity
• Genetic disorder - beckwith wiedeman (chrom 11)

Question 12

How should macrosomia be managed?

Answer 12

Exclude maternal DM

In the absence of polyhydramnios - treat preg as normal

Maternal DM - offer C-section

Anticipate shoulder dystocia (baby of DM mother, fat deposition on shoulders, higher risk)

Monitor for hypoglycaemia

Question 13

What risks are associated with a macrosomic baby?

Answer 13

Maternal

• Prolonged labour
• Operative delivery
• Postpartum haemorrhage
• Genital tract trauma

Fetal

• Birth injury
• Perinatal asphyxia
• Shoulder dystocia/erbs palsy
• Hypoglycaemia
• Childhood obesity
• Metabolic syndrome

Question 14

What causes IUGR symmetrical vs asymmetrical?

Answer 14

Sym = baby’s body is proportionally small

• Infections: CMV, rubella or toxoplasmosis
• Chromosomal abnormalities
• Anemia
• Maternal substance abuse (prenatal alcohol = Fetal alcohol syndrome)

Asym = baby has a normal-size head/brain, the rest of the body is small

• Pre-eclampsia
• Chronic HTN
• Severe malnutrition
• Genetic mutations: Ehlers–Danlos syndrome

Question 15

How can due date be estimated?

Answer 15

Naegele’s rule = first day of LMP - 3m, + 7d, + 1y