Small for gestational age

Question 1

How is small for gestational age defined?

Answer 1

Estimated foetal weight or abdo circumference <10th centile for gestational age when adjusted for maternal height, weight and ethnicity - considered severe if <3rd centile

• SGA foetuses are at risk of still birth, intrapartum hypoxia, neonatal complications, necrotising enterocolitis, impairment of neurodevelopment, obesity, CV disease and diabetes in later life.
• The majority of SGA foetuses are healthy but in very small foetuses the risk of complications is higher

Question 2

Epidemiology of small for gestational age

Answer 2

• 10% of foetuses are SGA
• 50-70% are small with no underlying pathology

Question 3

What are the causes of foetal growth restriction?

Answer 3

Placenta mediated: low maternal weight, substance abuse, pre-eclampsia and HTN, DM, kidney disease, autoimmune disease, thrombophilia

Non-placenta mediated: structural anomaly, chromosomal anomaly, inborn error of metabolism, congenital infection

Maternal factors: age, stress, undernutrition, HTN

Question 4

How is foetal growth restriction diagnosed?

Answer 4

• Growth restriction is initially suspected based on palpation of a symphysis fundal height smaller than expected
• Diagnosed by USS

Question 5

Investigations into foetal growth restriction

Answer 5

• Foetal weight estimated based on USS measurements of abdo circumference and femur length which is plotted on a customised chart
• Placental mediated growth restriction is associated with oligohydramnios (single deepest pool of amniotic fluid <2cm) this occurs because less nutrients travel from mother to foetus so foetus maintains blood supply to brain rather than other organs such as kidneys
• If a severe case of SGA is diagnosed <23 weeks further investigation is needed such as karyotyping, detailed anomaly scan, uterine artery Doppler, serological screening for CMV and toxoplasmosis, screening for syphilis and malaria

Question 6

Management of foetal growth restriction

Answer 6

• If umbilical Doppler normal, serial growth assessment is carried out every 2-4 weeks with planned delivery at 37 weeks
• If umbilical Doppler abnormal more regular monitoring is carried out and these foetuses are delivered by c-section because they do it tolerate labour