Fetal Biometry & Growth Assessment

During a growth scan, we focus on four primary measurements (biometry):

• Bipolar Diameter (BPD) and Head Circumference (HC): Measurements of the baby's head to assess brain development and gestational age.
• Abdominal Circumference (AC): The most sensitive measurement for checking fetal nutrition. The AC reflects the size of the liver and the amount of fat storage (glycogen), making it a key indicator of whether the baby is receiving enough nutrients from the placenta.
• Femur Length (FL): Measuring the longest bone in the body to monitor skeletal growth.

These four parameters are combined using a mathematical formula to calculate the Estimated Fetal Weight (EFW). We then plot this weight on a standardized growth chart (often tailored to the local population or specific to the mother's height and weight) to see which 'centile' the baby falls into.

While growth is assessed at every routine scan, formal 'Growth & Doppler' assessments are specifically required for:

• Maternal Health Issues: Like high blood pressure, pre-eclampsia, or gestational diabetes.
• Placental Concerns: If previous scans showed a small placenta or abnormal uterine artery Dopplers.
• Previous Pregnancy History: If a mother has previously delivered a very small (SGA) or very large (LGA) baby.
• Suspected Growth Deviation: If the 'fundal height' (measured by your midwife or obstetrician) does not match the weeks of pregnancy.

Monitoring growth is the most effective way to ensure the timing of delivery is optimized for the baby's safety.

Diagnosing a 'growth problem' requires looking beyond the numbers.

1. The Centile: A baby on the 50th centile is 'average' size. A baby below the 10th centile is considered 'Small for Gestational Age' (SGA), and above the 90th centile is 'Large for Gestational Age' (LGA).
2. Growth Velocity: If a baby was on the 70th centile at 28 weeks but has dropped to the 20th centile at 32 weeks, this 'crossing of centiles' is a significant clinical sign, even if the baby is still within the 'normal' range.
3. Functional Correlation: If growth is slow, we immediately perform Doppler studies to check the blood flow in the umbilical cord and brain to see if the baby is coping well with the placental supply.
4. Liquor Volume: We also measure the amniotic fluid ('liquor'). Low fluid levels often accompany poor growth, while excessive fluid can indicate issues like gestational diabetes.

Management is tailored to the growth pattern:

• For small babies (FGR): We increase the frequency of monitoring (sometimes weekly or twice-weekly) and use Dopplers to decide the safest time for delivery. The goal is to keep the baby in the womb as long as they are safe and growing, but to deliver before they become distressed.
• For large babies (Macrosomia): We focus on managing maternal blood sugar levels and planning for a delivery that minimizes the risk of birth complications like shoulder dystocia.
• Symmetric vs. Asymmetric Growth: We look at whether the whole baby is small (often a genetic trait or early infection) or if just the abdomen is small (typically a sign of placental 'starvation').

At the MFM Unit, our subspecialists provide the expert interpretation needed to distinguish a 'constitutionally small' healthy baby from one that is truly struggling.

Expert monitoring of fetal growth radically improves neonatal outcomes. By identifying babies who are not reaching their growth potential, we can prevent stillbirth and complications related to placental failure.

Furthermore, for parents of babies who are naturally 'big' or 'small' due to their own height and genetics, our detailed assessments provide the reassurance needed to avoid unnecessary interventions. Accurate EFW and growth velocity tracking allow for a calm, evidence-based approach to the final weeks of pregnancy and birth planning.

If your routine obstetrician has noted that your 'baby's tummy is measuring small' or if there is a 'drop in growth' on your chart, an immediate referral to the MFM Unit is essential.

Measuring a baby in the third trimester can be technically challenging due to the baby's position and the amount of fluid. Our subspecialists use high-end ultrasound machines and specialized software to achieve the most accurate EFW possible. We also provide the 'multimodal' assessment (combining growth, fluid, and Dopplers) that is required to make the most informed decision about your baby's wellbeing.