A growth scan, also known as a fetal growth or obstetric ultrasound, is a non-invasive medical imaging technique. It uses sound waves to create pictures of a developing baby within the uterus and the mother’s reproductive organs. This procedure monitors fetal development and well-being throughout pregnancy.
Standard Timing of Growth Scans
For uncomplicated pregnancies, a standard prenatal ultrasound occurs around 18 to 22 weeks of gestation. This scan, often called an anatomy scan, primarily examines the fetus’s organs and body structures. While its main purpose is anatomical assessment, initial growth parameters are established during this mid-pregnancy scan.
Dedicated growth scans, focused on assessing fetal size and growth, are not routinely performed in low-risk pregnancies. However, a healthcare provider may recommend them later in the third trimester if there are specific indications. Timing for these additional scans varies based on individual pregnancy factors and provider protocol.
Medical Reasons for Additional Scans
Healthcare providers recommend additional growth scans when specific medical indications or concerns arise. Maternal conditions like diabetes, high blood pressure, or kidney disease prompt closer monitoring of fetal growth. A history of complications in previous pregnancies, such as pre-eclampsia or stillbirth, also leads to more frequent growth assessments.
Fetal factors necessitate these scans, particularly for suspected issues with baby’s size. This includes concerns about the baby being smaller than expected for gestational age (small for gestational age or fetal growth restriction), or larger than average (large for gestational age or macrosomia). Discrepancies between fundal height measurements and gestational age, where uterus size does not match expected growth, can trigger a growth scan referral. Concerns about amniotic fluid volume (too little or too much) are reasons for a growth scan, as these can impact fetal well-being. Pregnancies with multiple fetuses, such as twins or triplets, routinely involve more frequent growth scans to monitor each baby’s development.
Placental issues, including insufficiency or abnormalities in location or structure, are common reasons for these ultrasounds. The placenta delivers nutrients and oxygen to the fetus, so concerns about its function warrant a growth scan. Abnormal screening test results can also indicate a need for further evaluation with a growth scan, assessing the baby’s overall health and development.
What a Growth Scan Assesses
During a fetal growth scan, key biometric measurements evaluate the baby’s size and growth. These measurements include head circumference (HC), abdominal circumference (AC), and femur length (FL). The biparietal diameter (BPD), the diameter across the head, is also recorded.
These biometric data points estimate fetal weight and track growth compared to typical curves for gestational age. Beyond measurements, the scan assesses amniotic fluid volume, often by calculating the Amniotic Fluid Index (AFI) or measuring the single deepest pocket. Placenta location and appearance are also evaluated. In cases with growth concerns, Doppler studies may assess blood flow in specific vessels, such as the umbilical artery, to evaluate the baby’s well-being.
Interpreting Scan Results
Most growth scans reveal normal development, reassuring expectant parents. If the scan indicates growth variations (smaller or larger than average for gestational age), further discussion with a healthcare provider is important. The estimated fetal weight derived from these measurements is an estimate and can vary.
Scan results are interpreted with other clinical information, including maternal health history, fundal height measurements, and previous scan findings. This comprehensive approach ensures a complete understanding of the baby’s health. If concerns arise, next steps may include repeat scans for continued monitoring, additional fetal well-being assessments, or specialist consultation. Discussions about delivery timing implications may also occur if significant concerns are identified.