Introduction
Fetal surveillance aims to find the fetus at risk of hypoxia or growth failure early enough to act. Methods range from counting movements to invasive sampling.
Ultrasound
- 1st trimester: viability, number of fetuses and chorionicity, dating, nuchal translucency.
- 2nd trimester (18–22 weeks): anomaly scan, placenta position, cervix length.
- 3rd trimester: growth (biometry, estimated fetal weight), amniotic fluid, presentation.
- Doppler: umbilical artery (placental resistance), middle cerebral artery (brain sparing; peak velocity for fetal anaemia), ductus venosus (late cardiac compromise).
- Biophysical profile: fetal breathing, movements, tone, amniotic fluid and NST, 2 points each; 8–10 is reassuring.
Cardiotocography (CTG)
CTG records the fetal heart rate together with uterine contractions.
- NST (non-stress test): CTG without contractions; reactive = at least 2 accelerations in 20 minutes.
- CST/OCT (contraction or oxytocin stress test): contractions induced with oxytocin or nipple stimulation; repeated late decelerations = positive, poor placental reserve. It is rarely used now that Doppler is available.
Invasive and other methods
- Fetal movement counting by the mother: reduced movements need same-day assessment.
A late deceleration with reduced variability is the CTG pattern of fetal hypoxia: it needs action, fetal blood sampling or delivery.