Maternal–Fetal Medicine
Core concepts
Maternal–fetal medicine integrates imaging, genetics, and physiology. Aneuploidy screening includes first-trimester combined screening, cell-free DNA, and second-trimester biochemistry; diagnostic testing requires chorionic villus sampling or amniocentesis. Ultrasound assesses growth, anatomy, amniotic fluid, placental location, and cervical length. Fetal growth restriction is an estimated fetal weight below the 10th centile with abnormal growth velocity or Doppler findings; umbilical artery Doppler distinguishes placental insufficiency. Middle cerebral artery Doppler helps assess fetal anemia. Multiple pregnancy requires chorionicity determination before 14 weeks. Preterm birth prevention includes progesterone for selected women, cervical cerclage for history or ultrasound-indicated cases, and antenatal corticosteroids between 24 and 34 weeks. Magnesium sulfate before 32 weeks reduces cerebral palsy. Isoimmunization is prevented with anti-D.
Traps
Do not equate a small fetus with growth restriction; constitutionally small fetuses may be healthy. In twins, dichorionic placentation has two separate placentas and a thick lambda sign; monochorionic has a T sign. In TTTS, the donor is oliguric and the recipient polyuric; Quintero staging guides therapy. Do not offer routine ovarian cancer screening, and do not confuse screening with diagnosis.
Worked example
A fetus at 30 weeks has an estimated weight below the 3rd centile, absent umbilical artery end-diastolic flow, and a normal middle cerebral artery pulsatility index. This is early-onset placental insufficiency. Management includes corticosteroids, close surveillance, and delivery if reversed flow, non-reassuring CTG, or worsening Doppler occurs, often after 32 weeks depending on local protocol.
Rule of thumb: in growth restriction, the umbilical artery reflects the placenta; the middle cerebral artery reflects the fetus.