Understanding the Fetal Well-being Scan at 36–40 Weeks

The fetal well-being scan, performed between 36 and 40 weeks of pregnancy, is a vital evaluation during the final weeks before delivery. This scan focuses on assessing the baby’s health and the readiness of the mother’s body for labour. While not always recommended for every pregnant woman, it plays a crucial role in ensuring safe delivery and identifying any last-minute complications that could affect the baby or the mother.

Why Is the Fetal Well-being Scan Done?

As the due date approaches, the fetal well-being scan helps monitor several factors critical for a healthy birth. Key reasons include:

• Monitoring Fetal Health: Ensuring the baby is thriving in the womb and not in distress.
• Assessing Growth and Weight: Checking if the baby’s size and weight align with gestational expectations.
• Evaluating Amniotic Fluid Levels: Detecting imbalances such as oligohydramnios (low fluid) or polyhydramnios (excess fluid), which may impact delivery.
• Placental Health: Ensuring the placenta is functioning properly and has not started deteriorating could compromise oxygen and nutrient delivery.
• Labour Preparation: Checking the baby’s position (head-down, breech, or transverse) and the status of the cervix.

What Does the Well-being Scan Reveal About the Baby?

This detailed scan provides vital insights into the baby’s condition, including:

• Fetal Position: Confirms whether the baby is in an optimal position for delivery. Determining the baby’s orientation, helps doctors plan for delivery.
• Fetal Movement and Heart Rate: Observes movements and breathing patterns, indicators of overall well-being and measures the heart rate to rule out distress.
• Fetal Size: Estimates weight and checks for size anomalies like macrosomia (large baby) or small-for-gestational-age (SGA). Fetal Growth Concerns (the baby is too small or too large) may require intervention or closer observation.
• Amniotic Fluid Volume: Confirms that fluid levels are appropriate for the baby’s needs.
• Umbilical Cord and Placenta: Evaluates blood flow in the umbilical cord and detects issues like the nuchal cord (cord around the neck). Identifies any signs of placental ageing, insufficiency, or abnormal placement of the placenta.
• Doppler Studies Measures blood flow in the umbilical cord and fetal brain, indicating whether the baby is receiving adequate oxygen and nutrients.

Why Is This an Important Scan?

At this late stage of pregnancy, the scan serves as a final check to confirm that the baby is thriving and the pregnancy is progressing smoothly. It allows for the identification of potential complications that could affect labour and delivery. By highlighting red flags, doctors can make timely decisions, whether that involves closer monitoring, changes in the delivery plan, or immediate interventions.

How Does a Fetal Wellbeing Scan Differ From Other Third-Trimester Scans?

Unlike earlier third-trimester scans, which may focus on growth patterns and anatomy, the 36–40-week wellbeing scan emphasizes:

• Labor Preparedness: Evaluating the baby’s position and signs of readiness for birth.
• Acute Complications: Detecting last-minute issues that may not have been present earlier.
• Placental Functionality: Ensuring the placenta is still supporting the baby adequately as it reaches the end of its functional lifespan.

Is This Scan Recommended for All Pregnant Women or Case-Specific?

The fetal wellbeing scan is not universally recommended for all pregnancies. Instead, it is typically suggested for pregnancies with identified risks or complications, such as:

• Women with conditions like hypertension, diabetes, or preeclampsia.
• Cases where earlier scans indicated concerns requiring follow-up.
• Those with abnormal fetal growth patterns identified earlier in the pregnancy.
• Pregnancies with multiple babies (e.g., twins or triplets).
• Women with a history of pregnancy complications.
• Overdue pregnancies to check amniotic fluid and placental health.

However, even in low-risk pregnancies, some healthcare providers may include it as a routine check to ensure optimal delivery conditions. In fact, in low-risk pregnancies,a routine ultrasound examination at 36 weeks' gestation was more effective than that at 32 weeks' gestation in detecting Fetal Growth Restrictions and related adverse perinatal and neonatal outcomes [1] .

Red Flags and Potential Issues Detected:

Some concerns that may be detected during this scan include:

• Fetal Growth Restriction (FGR): The baby is smaller than expected, indicating possible issues with placental function.
• Macrosomia: The baby is larger than normal, which could complicate delivery.
• Low or High Amniotic Fluid Levels: Abnormal fluid levels can indicate complications such as placental insufficiency or fetal kidney issues or gestational diabetes.
• Placental Problems: Signs of ageing, detachment (placental abruption), or abnormal placement, such as placenta previa. Premature ageing or insufficient blood flow may warrant early delivery.
• Umbilical Cord Issues: Abnormal blood flow or cord entanglement.
• Fetal Distress: Abnormal heart rates or reduced movements might indicate oxygen deprivation.
• Breech or Transverse Position: If the baby isn’t head-down, additional measures may be necessary, such as an external cephalic version (ECV) or scheduling a cesarean section.