Congenital abnormalities

1. Big picture

Congenital abnormalities are structural, chromosomal, genetic, or functional fetal disorders present before birth. In obstetrics, the examiner wants you to think like this:

Detect early → define severity → check genetics/infection/teratogen causes → counsel parents → plan pregnancy, delivery, neonatal care, or termination where appropriate.

Most mothers are asymptomatic. The abnormality is usually suspected by:

• abnormal first-trimester screening
• abnormal cell-free DNA screening
• abnormal maternal serum alpha-fetoprotein
• abnormal 18–22-week fetal anomaly scan
• abnormal amniotic fluid volume, fetal growth, hydrops, or fetal movements
• previous pregnancy affected by anomaly

The key exam distinction is:

Cell-free DNA is a highly sensitive screening test for common aneuploidies, but it is not diagnostic; positive screening should be followed by diagnostic testing if parents want certainty. Screening and diagnostic testing should be offered to all pregnant patients. ([ACOG][1])

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