Obstetric — 2nd/3rd trimester — Reference values: Amniotic fluid index (AFI), Biometry (BPD, HC, AC, FL), Calculator — amniotic fluid (AFI / deepest pocket).
| Measurement | Usual value | Note |
|---|---|---|
| Amniotic fluid index (AFI) | 5–25 cm | single deepest pocket normal: 2–8 cmSource: Ultrasoundpaedia / FMF |
| Biometry (BPD, HC, AC, FL) | — | use gestational-age tables (Hadlock/FMF) — no single valueSource: Hadlock / FMF |
| Range | AFI | Deepest pocket |
|---|---|---|
| Oligohydramnios | ≤ 5 cm | < 2 cm |
| Normal | 8–18 cm (5–24) | 2–8 cm |
| Polyhydramnios | ≥ 24 cm | ≥ 8 cm |
SMFM prefers the single deepest pocket (fewer false-positive oligohydramnios). Correlate with gestational age, growth and membrane integrity.
Source: Phelan/Moore (AFI) / SMFM / ISUOG
| Finding | Reading |
|---|---|
| Normal umbilical, normal MCA | Routine surveillance. |
| Umbilical PI >95th or MCA <5th or CPR <5th | Redistribution/resistance: increase surveillance. |
| Absent umbilical diastole (AEDF) | Advanced placental insufficiency. |
| Reversed umbilical diastole (REDF) | Severe: fetal medicine; ductus venosus/delivery per GA. |
Indices are gestational-age specific (FMF references). Absent/reversed umbilical diastole is the most severe sign.
Source: ISUOG Doppler guidelines / Delphi FGR consensus 2016
| Situation | Definition/sign | Management |
|---|---|---|
| Normally sited placenta | Edge ≥2 cm from internal os. | No restriction by location. |
| Low-lying placenta | Edge <2 cm from os, not covering. | Reassess in the 3rd trimester. |
| Placenta previa | Covers the internal os. | Cesarean; plan delivery. |
| Accreta spectrum (PAS) | Lacunae, loss of clear zone, hypervascularity, bulging (prior cesarean + previa). | Referral center; multidisciplinary team. |
Accreta risk rises sharply with previa over a cesarean scar. Document edge-to-os distance and invasion signs.
Source: FIGO PAS 2019 / ISUOG placenta previa & PAS guideline
| Cervix (transvaginal) | Reading |
|---|---|
| ≥ 25 mm | Low preterm birth risk. |
| 15–24 mm | Shortened: consider progesterone/follow-up. |
| < 15 mm or funneling | High risk: refer; discuss cerclage/pessary. |
Measure transvaginally, empty bladder, no excess pressure; use the shortest of 3. 25 mm cutoff in the 2nd trimester.
Source: FMF / SMFM / ISUOG cervical assessment
| Vessel/index | Abnormal | Meaning |
|---|---|---|
| Umbilical artery — PI | > 95th centile | increased placental resistance |
| Middle cerebral artery — PI | < 5th centile | redistribution (brain-sparing) |
| Cerebroplacental ratio (CPR) | < 10th centile | early placental insufficiency |
Indices are gestational-age specific (FMF references). Absent/reversed umbilical end-diastole = severe.
Source: FMF (Ciobanu 2019, UOG)