Having an ultrasound at 38 weeks of pregnancy is common and perfectly normal. While a third-trimester ultrasound is not a standard screening procedure for every low-risk pregnancy, it is frequently used to monitor fetal well-being as the due date approaches. This late-term scan provides healthcare providers with current, detailed information about the baby’s growth and immediate environment. The procedure is non-invasive and serves as a proactive measure to ensure a safe transition into labor and delivery.
Context: When Are Late-Term Ultrasounds Routine?
The decision to perform an ultrasound at 38 weeks often arises from the need for increased fetal surveillance in the final weeks of gestation. Although there is no universal protocol mandating a late third-trimester scan for all low-risk patients, many practices perform one as a general precaution. This timing is important because complications, such as a slowdown in fetal growth, can become apparent close to term.
A 38-week scan is most commonly initiated when a clinician identifies a specific indication or risk factor during routine prenatal visits. Indications include maternal conditions like high blood pressure or diabetes, or if the fundal height measurement is inconsistent with gestational age. Advanced maternal age or a history of prior obstetric complications also frequently lead to scheduling a late-term ultrasound.
Key Assessments: Analyzing Fetal Environment and Size
The late-term ultrasound focuses on specific measurements to assess the baby’s physical condition and the uterine environment. A primary check is the assessment of the amniotic fluid volume, quantified using the Amniotic Fluid Index (AFI) or the Maximum Vertical Pocket (MVP). Low fluid levels (oligohydramnios) can indicate placental issues and may necessitate closer monitoring or earlier delivery.
The scan also confirms the baby’s presentation, noting whether the baby is head-down (vertex), breech, or transverse, which directly impacts delivery planning. The sonographer calculates the Estimated Fetal Weight (EFW) using biometric measurements, such as head circumference, abdominal circumference, and femur length. This EFW helps identify if the baby is growing too slowly (fetal growth restriction) or too large (macrosomia), requiring careful consideration for the timing and method of delivery.
Monitoring Fetal Function: The Biophysical Profile
A 38-week ultrasound frequently incorporates elements of a Biophysical Profile (BPP) to assess fetal well-being and oxygen supply. The BPP is a scoring system that uses ultrasound to observe four distinct biophysical variables, often combined with a Non-Stress Test (NST) to monitor the fetal heart rate. The ultrasound specifically looks for fetal breathing movements, gross body movements, and adequate muscle tone.
These four variables, along with the assessment of the amniotic fluid volume, are each given a score (zero or two points), contributing to a maximum score of ten. A high BPP score, usually eight or ten, is highly reassuring, suggesting the baby is well-oxygenated and healthy. If initial observations are non-reassuring, a full BPP is often performed immediately to gain a complete picture of the baby’s status.
Interpreting Results and Clinical Guidance
The results of the 38-week ultrasound and any associated BPP guide the final clinical management plan. A reassuring result (normal fluid volume, appropriate fetal size, and a good BPP score) typically means the pregnancy can continue with routine weekly monitoring. This confirms the baby is thriving and ready for the natural onset of labor.
If the results are non-reassuring, such as a low BPP score or severe oligohydramnios, the healthcare team develops an immediate action plan. Depending on the severity of the findings, next steps may range from increased surveillance with repeat testing within 12 to 24 hours to scheduled induction of labor. If the baby’s well-being is immediately compromised, an urgent delivery, often via Cesarean section, may be indicated.