PU Cheat Sheet 2026

The 30 highest-yield PU facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. At what gestational age does the placenta normally migrate away from the cervical os? → By 28–32 weeks as the lower uterine segment develops
2. A double bubble sign on fetal ultrasound is diagnostic of which condition? → Duodenal atresia
3. Which bone is measured to assess femur length (FL) in fetal biometry? → The longest bone in the fetal thigh
4. What color Doppler setting adjustment is most important for detecting low-velocity venous flow? → Lowering the color velocity scale (PRF)
5. Which Doppler measurement is used in the biophysical profile scoring? → Doppler findings are not part of the standard biophysical profile
6. What does the pulsatility index (PI) calculation include that the S/D ratio does not? → Mean velocity in the denominator
7. What is typically assessed in the maternal ovaries during an ultrasound? → Presence of cysts or other abnormalities
8. In a naturally conceived triplet pregnancy, what is the most common chorionicity-amnionicity configuration? → Trichorionic-triamniotic
9. What crown-rump length (CRL) corresponds to the first detectable fetal cardiac activity? → 2–4 mm (approximately 5.5–6 weeks)
10. A hyperechoic bowel finding on second-trimester ultrasound may indicate which condition? → Cystic fibrosis, Down syndrome, or cytomegalovirus infection
11. The cephalic index (CI) is calculated as which ratio? → BPD divided by occipitofrontal diameter × 100
12. Which measurement is considered the most accurate indicator of gestational age in the second trimester? → Biparietal diameter (BPD)
13. At what atrial width measurement is ventriculomegaly diagnosed? → Greater than 10 mm
14. A fetus measuring below which percentile is typically classified as small for gestational age (SGA)? → 10th percentile
15. Which ultrasound finding best distinguishes dichorionic-diamniotic (DCDA) twins from monochorionic-diamniotic (MCDA) twins in the first trimester? → Twin peak (lambda) sign at placental insertion
16. What is the significance of an abdominal circumference crossing two major percentile lines downward on a growth chart? → It suggests developing IUGR requiring further evaluation
17. What is the significance of the Doppler function in ultrasound? → It detects and evaluates blood flow.
18. What ultrasound finding definitively differentiates monochorionic-monoamniotic (MCMA) twins from monochorionic-diamniotic (MCDA) twins? → Complete absence of any dividing membrane between the twins
19. Acardiac twinning (twin reversed arterial perfusion — TRAP sequence) occurs exclusively in which type of twin pregnancy? → Any monochorionic twin pregnancy regardless of amnionicity
20. What is the normal range for amniotic fluid index (AFI) in a term pregnancy? → 8–24 cm
21. What ultrasound finding suggests renal agenesis as a cause of oligohydramnios? → Absent or severely abnormal kidneys with no bladder filling
22. The 'T-sign' on ultrasound at the placental insertion of the inter-twin membrane is associated with which type of twin placentation? → Monochorionic-diamniotic
23. Which cardiac abnormality is most commonly detected on the four-chamber view of the fetal heart? → Hypoplastic left heart syndrome
24. What does the resistance index (RI) measure in Doppler assessment? → (Systolic - Diastolic) / Systolic velocity
25. What does M-mode ultrasound assess in the first trimester? → Fetal cardiac activity and heart rate
26. What AFI value defines oligohydramnios? → Less than 5 cm
27. Which vessel is sampled in the ductus venosus Doppler assessment? → The fetal venous connection between the portal vein and inferior vena cava
28. Which ultrasound finding is associated with congenital diaphragmatic hernia (CDH)? → Stomach and bowel in the chest alongside the heart
29. What is a succenturiate lobe of the placenta? → An accessory placental lobe separate from the main placenta
30. Which marker on second-trimester ultrasound is associated with Down syndrome (Trisomy 21)? → Absent or hypoplastic nasal bone