Fetal Skull Flashcards
(18 cards)
Which of the following is the largest diameter of the fetal head?
Occipitomental
Sinciput
anterior portion of the fetal skull
• Located between the brow (just above the eyes) and the fontanelles
Biparietal Diameter
• Biparietal Diameter (BPD) = distance between the two parietal bones of the fetal skull
• Widest transverse diameter of the fetal head
• Measured via ultrasound to assess gestational age and fetal size
• In vertex presentation, it is the optimal diameter for passing through the pelvis
• Average at term: ~9.5 cm
Cranial
sutures
• Cranial sutures are the fibrous joints between the bones of the fetal skull
• Allow bones to overlap (mold) during birth
• Help providers determine fetal position and presentation during vaginal exams
Major Sutures:
• Sagittal – Between parietal bones
• Coronal – Between frontal and parietal bones
• Lambdoid – Between parietal and occipital bones
• Frontal (metopic) – Between the two frontal bones
Fontanelles
• Fontanelles = soft spots where cranial sutures meet
• Allow for molding of the fetal head during birth
• Help determine fetal position during vaginal exams
Anterior Fontanelle
• Diamond-shaped
• Where sagittal, coronal & frontal sutures meet
• Closes by ~18 months
Posterior Fontanelle
• Triangle-shaped
• Where sagittal & lambdoid sutures meet
• Closes by ~2–3 months
The posterior transverse suture is called the:
lambdoidal suture
The anterior transverse suture is called the:
coronal suture
The anterior posterior suture is called the:
sagittal suture
Which of the following is the largest diameter of the fetal head?
Occipitomental
What is the vertex?
Vertex = area between the anterior and posterior fontanelles
• Represents the optimal presenting part in labor (well-flexed head)
• Suboccipitobregmatic diameter presents (≈9.5 cm)
What is the sinciput?
Sinciput = fetal forehead region
• Presents in a partially extended head (military attitude)
• Larger diameter than vertex, may slow labor
What is the Mentum?
Mentum = the chin of the fetus
• Presenting part in face presentation (fully extended head)
• Vaginal birth possible only if mentum anterior (chin rotates under pubic bone)
What is the anterior fontanelle?
• Largest soft spot on a newborn’s skull
• Located at the junction of the two frontal and two parietal bones
• Allows skull bones to overlap during birth (molding)
• Provides space for brain growth after birth
• Typically closes between 12 to 18 months of age
What is the posterior fontanelle?
• Smaller soft spot on a newborn’s skull
• Located at the junction of the two parietal bones and the occipital bone
• Allows skull bones to overlap during birth (molding)
• Provides some flexibility for brain growth
• Typically closes within 6 to 8 weeks after birth
What is the shape difference between the anterior and posterior fontanelles?
• Anterior fontanelle: Diamond or kite-shaped
• Posterior fontanelle: Triangular-shaped
