Midpregnancy Anatomy Ultrasound: What to Expect

Understanding Your Midpregnancy Anatomy Ultrasound

The midpregnancy anatomy scan represents one of the most anticipated and medically significant milestones in pregnancy. Typically performed between 18 and 22 weeks of gestation, this detailed ultrasound examination provides crucial insights into fetal development and maternal health. Unlike earlier pregnancy scans that focus primarily on confirming pregnancy viability and dating, the anatomy scan conducts a systematic evaluation of virtually every major fetal structure and system. This comprehensive imaging procedure plays a foundational role in modern prenatal care by enabling early detection of developmental concerns and allowing healthcare providers to make informed recommendations about ongoing pregnancy management.

The Purpose Behind Your Midpregnancy Screening

The anatomy scan serves multiple important functions beyond simple reassurance about your baby’s development. Healthcare providers use this examination to establish baseline measurements of fetal growth, verify that the placenta is positioned appropriately for optimal nutrient and oxygen delivery, and assess the volume of amniotic fluid surrounding your developing baby. Perhaps most significantly, the scan systematically screens for 11 specific conditions that may warrant further evaluation or specialized care during pregnancy and after birth.

This screening is particularly valuable because detecting potential concerns early allows for better preparation and planning. Whether you need to consult with maternal-fetal medicine specialists, arrange for specialized pediatric care at delivery, or simply gain peace of mind about your baby’s structural development, the information gathered during this scan provides an essential foundation for your prenatal care plan.

What Specific Conditions Are Evaluated During the Scan

The anatomy scan screens for 11 significant conditions that can be identified through ultrasound imaging. Understanding what your healthcare provider is looking for can help you appreciate the importance of this detailed examination:

• Anencephaly: A severe condition where major portions of the fetal brain and skull fail to develop properly
• Open spina bifida: A neural tube defect affecting spinal cord closure and development
• Cleft lip and palate: A separation in the upper lip and roof of the mouth that may affect feeding and speech
• Diaphragmatic hernia: An opening in the diaphragm allowing abdominal organs to enter the chest cavity
• Gastroschisis: A condition where loops of the intestine protrude through an opening in the abdominal wall
• Exomphalos: A defect where abdominal organs remain partially outside the body within a membrane sac
• Serious cardiac abnormalities: Structural heart defects that may require intervention before or after birth
• Bilateral renal agenesis: The absence of both kidneys, a condition requiring specialized management
• Severe skeletal dysplasia: Significant bone development abnormalities affecting skeletal formation
• Edwards’ syndrome (trisomy 18): A chromosomal condition associated with multiple physical abnormalities
• Patau’s syndrome (trisomy 13): Another chromosomal condition with various developmental implications

Comprehensive Fetal Structures Examined During Your Scan

The anatomy scan involves a systematic examination of virtually every major structure in your developing baby. Skilled sonographers follow established protocols to ensure consistent and thorough evaluation across all patients.

Brain and Neurological Development

The fetal brain undergoes remarkable development during the second trimester. Sonographers assess the lateral ventricles, which are fluid-filled chambers deep within the brain, looking for appropriate size and symmetry. The cavum septi pellucidi, a normal fluid collection between specific brain structures, becomes visible around 16 weeks and serves as an important anatomical landmark. The cerebellum, responsible for balance and coordination, is measured for appropriate size. Additionally, the cisterna magna, a fluid space at the back of the brain, is assessed to ensure measurements fall within normal parameters of 2 to 10 millimeters.

Facial Structures and Appearance

The facial profile provides important information about fetal development. Sonographers evaluate the forehead, nose, lips, and chin for proper formation and proportion. The examination specifically screens for cleft lip and palate, conditions affecting the upper lip and roof of the mouth that may be visible on ultrasound imaging. The eye orbits are assessed for appropriate size and position, and the ears are examined for normal development.

Spine and Spinal Cord

The spine is evaluated in multiple imaging planes to ensure proper vertebral alignment and closure. Sonographers look for the characteristic appearance of ossified vertebral bodies, which appear as parallel echogenic lines running the length of the spine. The examination specifically screens for spina bifida and other neural tube defects that affect spinal column closure. The sacrum, which forms the base of the spine, is also assessed during this evaluation.

Cardiac Structure and Function

The fetal heart, beating at approximately 140 to 160 beats per minute during the second trimester, receives detailed scrutiny during the anatomy scan. Sonographers assess the four chambers of the heart, the valves controlling blood flow between chambers, and the major vessels carrying blood to and from the heart. The examination evaluates the relationship of the heart to other chest structures and screens for serious cardiac abnormalities that might require specialized pediatric care.

Abdominal Organs and Systems

The fetal abdomen contains several critical organs requiring careful evaluation. The stomach is identified in its normal position on the left side of the abdomen, confirming proper situs (organ positioning). The kidneys, positioned on either side of the spine, are measured and assessed for normal size and appearance. The bladder is visualized as a small fluid-filled structure in the lower abdomen. The umbilical cord insertion site is examined carefully to exclude abdominal wall defects such as gastroschisis or exomphalos, conditions where abdominal contents are not fully enclosed.

Limbs, Hands, and Feet

Each arm and leg is measured and assessed for proper bone development and length. The hands and feet are examined for appropriate number and positioning of digits. The long bones of the legs, particularly the femur (thighbone), are measured as indicators of appropriate fetal growth proportionate to the head size. Sonographers assess whether the limbs appear symmetrical and whether movement appears appropriate and unrestricted.

Additional Maternal and Placental Assessments

While the fetal anatomy comprises the primary focus of the scan, the examination also provides important information about maternal structures and the pregnancy environment:

• Placental location: Confirmation that the placenta is positioned in a location that will not obstruct vaginal delivery or compromise fetal nutrition
• Amniotic fluid volume: Assessment of the fluid surrounding the baby to ensure adequate cushioning and space for movement
• Cervical length: Measurement of the cervix to screen for potential preterm labor risk
• Uterine blood flow: Evaluation of blood vessels supplying the uterus to ensure adequate placental perfusion
• Maternal pelvic organs: Assessment of overall uterine health and any structural concerns that might affect pregnancy management

How the Scanning Process Works

Understanding the technical aspects of the anatomy scan can help you feel more comfortable during your appointment. A trained sonographer performs the examination using ultrasound technology that transmits high-frequency sound waves through your abdomen. These sound waves reflect off fetal structures and return to the transducer (handheld probe) to create detailed two-dimensional grayscale images on a screen.

The scan typically requires 30 to 45 minutes, though duration varies depending on fetal position, maternal body composition, and whether the sonographer can obtain all necessary images. You’ll lie on an examination couch in a dimly lit room while the sonographer applies warm gel to your abdomen. This gel facilitates sound wave transmission and allows the probe to move smoothly across your skin. The sonographer will systematically move the probe across your abdomen, pausing at specific anatomical landmarks to obtain measurements and assess structures. You may experience some discomfort as the sonographer applies pressure to optimize image quality, but the procedure is entirely non-invasive and poses no known risk to your developing baby.

Interpreting Your Anatomy Scan Results

After your scan, a physician reviews the sonographer’s images and measurements to provide you with results. Most pregnancies progress normally with no abnormalities detected. In these cases, you’ll receive reassurance about your baby’s structural development and a report confirming that measurements are consistent with your expected delivery date.

If the sonographer is unable to obtain clear visualization of a particular structure—perhaps because your baby is in an awkward position or amniotic fluid volume limits imaging—you may be asked to return for a follow-up scan. This is a common occurrence and rarely indicates a problem; it simply means your baby didn’t cooperate during the initial examination. Scheduling a repeat scan a week or two later often allows clearer visualization when your baby has moved to a more favorable position.

Should the scan identify a potential concern, your healthcare provider will discuss findings in detail and explain what additional evaluation or monitoring might be recommended. Some findings may resolve spontaneously as pregnancy progresses, while others might warrant consultation with maternal-fetal medicine specialists or pediatric subspecialists to optimize your pregnancy management and birth planning.

Determining Fetal Sex During Your Anatomy Scan

Many parents choose to learn their baby’s biological sex during the anatomy scan. If you’re interested in this information, the sonographer can typically provide a determination with reasonable accuracy by 18 weeks of gestation. The examination looks at external genital structures visible on ultrasound. However, it’s important to understand that no imaging technique is 100 percent accurate, and occasionally the information provided during the scan may not match the baby’s actual sex at birth, particularly if imaging quality was limited or fetal position was unfavorable for clear visualization.

Preparing for Your Anatomy Scan Appointment

Simple preparation steps can help ensure your scan proceeds smoothly and images are of optimal quality. A full bladder can help push the uterus into a more favorable position for imaging, so consider drinking water before your appointment. Wear comfortable clothing that allows easy access to your abdomen. Arrive early to complete any necessary paperwork and discuss your medical history. Consider bringing your partner, a family member, or a friend for support and to help you process information during the appointment. Some facilities allow you to record the scan or take images to share with loved ones.

Frequently Asked Questions About the Anatomy Scan