Can fetal anomalies be detected prior to birth?

Prenatal Detection of Fetal Anomalies

Yes, most fetal anomalies can be detected prior to birth through routine prenatal screening and specialized imaging techniques, with ultrasound being the primary diagnostic tool. 1

Timing and Methods of Detection

First Trimester (11-14 weeks)

• Approximately 44% of fetal anomalies can be detected during first trimester screening 2
• Increased nuchal translucency at 10-14 weeks can be an early sign of severe skeletal dysplasia 1
• Major abnormalities reliably detectable at this stage include:
  • Acrania/anencephaly
  • Abdominal wall defects
  • Holoprosencephaly
  • Cystic hygromata 3
• Cardiac examination capability increases from 20% at 11 weeks to 92% at 13 weeks 2

Second Trimester (18-22 weeks)

• This is the optimal time for detecting most fetal anomalies 1
• Most severe skeletal dysplasias are detected during routine ultrasound at 18-20 weeks 1
• Detection rate increases to approximately 74% compared to first trimester 2
• Ultrasound performed before 18 weeks is more likely to result in incomplete anatomic surveys 4
• Factors affecting detection:
  • Maternal BMI (higher BMI reduces visualization)
  • Fetal position
  • Equipment quality
  • Sonographer experience 1, 4

Types of Anomalies Detectable

Central Nervous System

• Brain anomalies (hydrocephalus, holoprosencephaly)
• Spinal defects (spina bifida, anencephaly) 1, 3

Cardiovascular System

• Congenital heart defects
• Cardiac structures are among the most commonly incompletely visualized 4

Gastrointestinal System

• Abdominal wall defects (gastroschisis, omphalocele)
• Echogenic bowel (requires follow-up ultrasound at 32 weeks) 1, 5

Genitourinary System

• Renal anomalies (30-50% of all structural anomalies present at birth) 6
• Urinary tract obstructions 1, 6

Skeletal System

• Short limb length (femur or humerus length <5th percentile)
• Angular deformity of long bones 1
• Key measurements for skeletal dysplasias:
  • Chest-to-abdomen ratio
  • Femur length to abdominal circumference ratio 1

Advanced Imaging Techniques

Detailed Ultrasound

• Indicated when anomalies are suspected or detected on routine screening 1
• 3D ultrasound can assist in assessment of facial features characteristic of certain disorders 1

Fetal MRI

• Recommended when ultrasound findings are inconclusive 1, 5
• Particularly valuable for:
  • Central nervous system anomalies
  • Planning for prenatal and postnatal intervention
  • Airway management in fetuses with neck masses
  • Lung volume measurement in congenital diaphragmatic hernia
  • Pre-surgical planning for spina bifida repair 1, 3, 6

Genetic Testing

• Prenatal next-generation skeletal panel gene sequencing or whole exome/genome testing should be offered to increase diagnostic yield in suspected skeletal dysplasia 1
• Chromosomal microarray is recommended over routine karyotype when major structural abnormalities are detected 3

Clinical Implications

Follow-up Protocol

• When soft markers are found, detailed ultrasound examination should be performed to look for additional markers and anomalies 1
• Follow-up ultrasound at 32 weeks is recommended for certain findings like pyelectasis, short humerus/femur length, and echogenic bowel 1, 5

Delivery Planning

• Fetuses with prenatally detected congenital anomalies should be delivered at tertiary care centers with facilities for neonatal surgery and pediatric intensive care 7
• Most anomalies do not require preterm delivery 7
• Only specific conditions warrant cesarean section as primary mode of delivery:
  • High-risk sacrococcygeal teratoma
  • Congenital lung masses with significant fetal compromise
  • Neural tube defects with head circumference >40 cm
  • Gastroschisis with extracorporeal liver
  • Giant omphaloceles 7

Limitations and Caveats

• Detection rates vary by organ system and depend on equipment settings and sonographer experience 3
• Maternal obesity significantly reduces visualization and detection rates 4
• Some anomalies may not be evident until later in pregnancy due to ongoing development of organ systems 3
• Cardiac structures and spine are the most commonly incompletely visualized areas 4
• Plain radiography should be avoided prenatally due to radiation exposure 1

By utilizing a systematic approach to prenatal imaging and following established guidelines for timing and techniques, most significant fetal anomalies can be detected before birth, allowing for optimal perinatal management and improved outcomes.