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Expert Advice

Is your baby not achieving its full growth potential? By Dr Tan Toh Lick

FETAL GROWTH RESTRICTION

Fetal growth restriction (FGR) is used to describe a baby fetus that has not achieved its full growth potential. Another commonly used terminology for FGR is intrauterine growth restriction (IUGR).

The reason for FGR may be due to the fetus, placenta, mother or a combination of these. Pregnancy at risk of FGR includes a fetus with genetic abnormalities, infection, multiple pregnancies; umbilical cord and placental abnormalities such as a single umbilical artery; maternal medical conditions such as pre-eclampsia, diabetes, bleeding in pregnancy; exposure to teratogens, alcohol, tobacco and air pollution. While the air may be fresher at high altitudes, the lower oxygen level results in lower birth weight. IVF pregnancy, short interval between pregnancies, and extremes of maternal age are more likely to have a small baby.

SCREENING FOR FGR

One of the purposes of antenatal care is to screen for FGR as intervention can reduce problems associated with FGR.

Routine screening generally involves measuring the symphysis-fundal height (SFH) at each visit after 24 weeks. A difference of more than 3 cm compared to gestational age in weeks such as SFH 30 cm at 34 weeks pregnancy, or static serial measurement is considered abnormal. This method for detecting FGR is affected by the woman’s size, the number of previous pregnancies and ethnicity.

An alternative technique of screening for FGR involves ultrasound growth scan(s) for abdominal circumference (AC) and/or estimated the fetal weight (EFW) in the third trimester such as at 34 weeks, or 31 and 36 weeks. This method is generally used in women with risk factors for FGR. A slowdown in the growth of the fetus in serial scans suggests FGR and warrants further evaluation. FGR is also suggested in women with a single scan showing AC or EFW below the 10^th centile. However, this single measurement does not differentiate between a fetus that is normally small and that with FGR, particularly if customized growth curves are not used.

IMPLICATIONS OF FGR

Fetuses affected by FGR are more likely to have poor outcomes. These include a 6-fold increase in stillbirth, a 5-fold increase in neonatal death, and a 5-fold increase in small for gestational age at birth. In the longer term, these individuals affected by FGR are more likely to develop obesity, diabetes, heart and kidney disease.

Mothers with FGR pregnancies appear to double their risk of ischemic heart disease and mortality.

INVESTIGATIONS TO DETERMINE THE CAUSE(S) OF FGR

When FGR is diagnosed, clinical assessment is performed to determine the cause(s).

The health, diet, and lifestyle of the mother are explored to determine if there is any factor that predisposes her to have an FGR pregnancy. Conditions such as pre-eclampsia will need to be managed separately, while conditions such as poor diet and smoking can be potentially changed.
A detailed fetal anatomic scan is required to detect anomalies such as omphalocele, gastroschisis, diaphragmatic hernia, skeletal dysplasia, and congenital heart defects.
Where FGR is present early (before 24 weeks), severe (below 5^th percentile), or symmetrical (where both the head and abdomen are small), then a genetic cause is suspected. Similarly, if there are major fetal structural abnormalities or soft markers associated with aneuploidy, then genetics studies are warranted. This typically involves amniocentesis for karyotype or chromosomal microarray analysis.
Infections such as cytomegalovirus, toxoplasmosis, rubella, varicella, and syphilis can result in FGR. Where clinical assessment or fetal ultrasound findings suggest such infection, maternal blood screening for these relevant infections, and amniotic fluid DNA testing as indicated by the clinical setting are warranted.
Mosquito-borne infections such as malaria, dengue and zika can also result in FGR and should be considered in women with high fever and risk of exposure.

MANAGEMENT OF FGR DUE TO UTEROPLACENTAL INSUFFICIENCY

The majority of FGR pregnancies are due to inadequate transfer of nutrients and oxygen from the mother to the fetus (uteroplacental insufficiency) and therefore would be structurally and chromosomally normal.

There is no robust evidence that any intervention or bed rest in healthy women improves the growth of FGR fetuses. Therefore, management of FGR due to uteroplacental insufficiency generally involves regular fetal assessments to identify fetuses that are at high risk of stillbirth or neonatal morbidity so that interventions can be planned.

Fortnightly ultrasound scans for EFW and umbilical artery (UA) doppler are arranged until delivery around 37 weeks if the findings are normal. Fetal heart rate monitoring (Cardiotocography, CTG) and amniotic fluid measurement can be used to complement ultrasound surveillance.

If the UA doppler is abnormal, then twice weekly to daily UA doppler monitoring together with ductus venosus (DV) doppler or middle cerebral artery (MCA) doppler before or after 32 weeks respectively is indicated. Should there be abnormal MCA doppler after 37 weeks, no growth over 3 weeks after 34 weeks, or there is absent reversed end-diastolic velocity (AREDV) UA doppler after 32 weeks, or abnormal DV dopplers and/or abnormal CTG after 24 weeks, then delivery should be considered.

PLANNING THE BIRTH

If the fetus has AREDV in the UA doppler, delivery by caesarean section is recommended. In other situations, induction of labour is feasible unless there is another indication for caesarean section. Continuous CTG is recommended in labour as fetal distress is common in FGR pregnancies.

A course of corticosteroids should be given if delivery is planned before 36 weeks. For delivery before 32 weeks, magnesium sulphate is recommended before delivery for the neuroprotection of the baby.

CARE AFTER BIRTH

In the absence of associated complications such as pre-eclampsia, post-natal care is routine for the mother.

PLANNING FOR THE NEXT PREGNANCY

Women with FGR pregnancies are more likely to experience FGR as well as preterm delivery, pre-eclampsia, placenta abruption and stillbirth in subsequent pregnancies.

All women planning to conceive should consider preconception counselling to optimize their health and readiness for pregnancy. Cessation of smoking and alcohol intake, folic acid, a good diet, as well as food and hand hygiene are important.

In women with previous FGR pregnancies, ultrasound dating in the first trimester with intermittent ultrasound monitoring of fetal growth in the second and third trimester is recommended.

Anti-coagulants, anti-hypertensives, progesterone, calcium supplements or bedrest do not prevent FGR. However, in women whose FGR is due to pre-eclampsia, or in women who have risk factors for pre-eclampsia, starting low-dose aspirin by 16 weeks can reduce the risk of FGR.

DR TAN TOH LICK, MBBS (LONDON), FRCOG (UK)

Dr Tan Toh Lick graduated from King’s College School of Medicine and Dentistry, the University of London in 1997. He undertook his Obstetrics and Gynaecology Specialist Training in London and was appointed Consultant Obstetrician and Gynaecologist in 2008. As a consultant, his contributions to service development, patient care and staff training were widely recognised and he was awarded 3 Clinical Excellence Awards in 2010 and 2012 in the United Kingdom. After he relocated to Singapore in 2013, he was awarded the Singapore Health Quality Service Award in 2015, Singapore.

Dr Tan now consults at Thomson Women’s Clinic (JEM) and Thomson Surgical Centre (Thomson Medical Centre). He continues to be active in his academic work organizing 2 CME courses “Your Woman Matters” for family physicians and “PROMPT4 – The Tetralogy” for maternity specialists, as well as publishing in medical journals and public magazines.

FURTHER READING

1. Royal College of Obstetricians and Gynaecologists. The Investigation and Management of the Small–for–Gestational–Age Fetus. Green-top guideline no 31. London RCOG 2014

2. Low dose aspirin use during pregnancy. ACOG Committee Opinion No 743. American College of Obstetricians and Gynecologist. Obstet Gynecol 2018; 132: e44-52