Ultrasound imaging is a non-invasive method in prenatal care that monitors fetal development throughout pregnancy. This technology uses sound waves to create images of the baby within the womb, providing valuable insights into their growth and well-being. It helps healthcare providers track progress and assess the fetus.
Purpose of a 28-Week Ultrasound
While not routine for every pregnancy, a 28-week ultrasound is often recommended, especially when specific information about fetal development is needed. This scan, often called a third-trimester or growth scan, assesses fetal growth patterns, ensuring the baby is developing as expected and identifying any potential deviations.
The scan also evaluates the volume of amniotic fluid, which is important for fetal movement and lung development. Healthcare providers check the placenta’s health and location, particularly if there were earlier concerns like a low-lying placenta. Confirming the baby’s position in the uterus is another important aspect, as it influences birth planning. This ultrasound is common in pregnancies with certain considerations, including a history of small or large babies, conditions like gestational diabetes or high blood pressure, or concerns about the baby’s size based on external measurements.
Key Measurements and Observations
During a 28-week ultrasound, specific biometric measurements assess fetal growth. These include head circumference (HC), which gauges head size, and abdominal circumference (AC), an indicator of fetal nutrition and organ development. Femur length (FL), the longest bone, is also measured for skeletal development and overall growth. These measurements are compared against standard charts to track the baby’s growth.
Amniotic fluid volume is another important component. This is typically done using methods like the Amniotic Fluid Index (AFI) or by measuring the single deepest vertical pocket (SDP). AFI involves dividing the uterus into four quadrants and summing the largest vertical fluid pockets in each. The deepest pocket method measures the largest single pocket of fluid free from the umbilical cord or fetal parts.
The placenta’s position and appearance are re-evaluated to ensure it is not obstructing the cervix, a condition known as placenta previa. The scan also confirms the baby’s presentation, noting whether the baby is head-down (cephalic), bottom-down (breech), or lying sideways (transverse). Visual observations of fetal movement and general well-being are also made.
Interpreting Results and Next Steps
Interpreting 28-week ultrasound findings involves comparing measurements and observations to established normal ranges for this gestational age. For fetal growth, babies typically fall between the 10th and 90th percentile for their estimated weight. Variations in measurements are common and do not automatically indicate a problem, as individual growth patterns differ.
Amniotic fluid levels are assessed against normal values. An Amniotic Fluid Index (AFI) between 8 and 18 cm is generally typical at this stage, and a single deepest pocket measurement between 2-8 cm is also considered normal. Significant deviations, such as very low (oligohydramnios) or very high (polyhydramnios) fluid levels, may warrant further investigation. Similarly, if the placenta is still low-lying or covering the cervix, continued monitoring may be necessary.
If the ultrasound reveals findings outside the typical range, healthcare providers will discuss the implications and determine appropriate next steps. This might include scheduling repeat scans to monitor growth, ordering additional tests like a glucose tolerance test if a large baby is suspected, or adjusting prenatal care to address specific concerns. The healthcare team will provide detailed explanations of all findings and guide the pregnancy journey.