Fronto-Occipital Index (FOI)

Definition: Ratio of the occipitofrontal diameter (OFD) to the biparietal diameter (BPD), expressed as a percentage.

Plane: Axial plane of the fetal head at the level of the thalami and cavum septi pellucidi, ensuring symmetric hemispheres and visualization of midline falx.

Calculation: FOI = (OFD / BPD) × 100

Normal Range: Typically 70–85%. - FOI < 70% → Suggests brachycephaly. - FOI > 85% → Suggests dolichocephaly.

Clinical Use: Assesses skull shape and head molding; useful in differentiating abnormal skull configurations which may affect BPD reliability in gestational age estimation.

Normal Range: 70% – 85%

Gestational Age (Weeks)	Expected FOI (%)	Interpretation
14	70 – 85	Normal
16	70 – 85	Normal
18	70 – 85	Normal
20	70 – 85	Normal
22	70 – 85	Normal
24	70 – 85	Normal
26	70 – 85	Normal
28	70 – 85	Normal
30	70 – 85	Normal
32	70 – 85	Normal
34	70 – 85	Normal
36	70 – 85	Normal
38	70 – 85	Normal
40	70 – 85	Normal

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Note: If you select English, answer all questions in English.
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1. What does FOI stand for in fetal ultrasound? 1. भ्रूण अल्ट्रासाउंड में FOI का क्या अर्थ है?
A. Fetal Orbital Index
B. Fronto-Occipital Index
C. Fetal Ossification Index
D. Frontal Orientation Index

2. What is the formula of FOI? 2. FOI का सूत्र क्या है?
A. (BPD / OFD) × 100
B. (OFD / BPD) × 100
C. (HC / AC) × 100
D. (FL / BPD) × 100

3. Which parameters are used to calculate FOI? 3. FOI की गणना के लिए किन पैरामीटरों का उपयोग किया जाता है?
A. HC and AC
B. FL and AC
C. BPD and OFD
D. CRL and FHR

4. What does an abnormal FOI value suggest? 4. असामान्य FOI मान किसकी ओर संकेत करता है?
A. Cranial shape abnormality
B. Placental insufficiency
C. Polyhydramnios
D. Cardiac malformation

5. FOI is commonly used to assess which condition? 5. FOI का सामान्यत: किस स्थिति के मूल्यांकन के लिए उपयोग किया जाता है?
A. Hydrocephalus
B. Craniosynostosis
C. Cephalic index variations
D. All of the above

6. Which imaging plane is required for measuring BPD and OFD? 6. BPD और OFD मापने के लिए किस इमेजिंग प्लेन की आवश्यकता होती है?
A. Coronal plane
B. Axial plane
C. Sagittal plane
D. Oblique plane

7. A normal FOI range is approximately: 7. FOI का सामान्य मान लगभग कितना होता है?
A. 60–70
B. 70–85
C. 85–95
D. 95–110

8. If FOI is significantly increased, it may indicate: 8. यदि FOI काफी बढ़ा हुआ है, तो यह किस ओर संकेत करता है?
A. Dolichocephaly
B. Brachycephaly
C. Hydrocephalus
D. Normal skull

9. FOI values lower than normal usually indicate: 9. सामान्य से कम FOI मान आमतौर पर किस ओर संकेत करता है?
A. Dolichocephaly
B. Brachycephaly
C. Plagiocephaly
D. Hydrocephalus

10. Which fetal biometric index is closely related to FOI? 10. कौन सा भ्रूण बायोमेट्रिक इंडेक्स FOI से निकटता से संबंधित है?
A. Cephalic Index (CI)
B. HC/AC ratio
C. FL/AC ratio
D. Ponderal Index

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Fronto-Occipital Index (FOI)

OFD (mm)

BPD (mm)

FOI = —

Formula: FOI = (OFD / BPD) × 100   |   Normal: 70–85%