Obstetrics and Gynecology - A.M. Hromova 2000

Fertilization and Fetal Development
Development of the Zygote
Structure and Dimensions of a Full-Term Fetus

The fetal cranium consists of the following bones: two frontal bones, two parietal bones, two temporal bones, the Occipital bone, the Sphenoid bone, and the Ethmoid bone. The sutures on the newborn's HEAD include: the frontal (metopic) suture between the frontal bones; the sagittal suture between the parietal bones; the coronal suture between the frontal and parietal bones; and the lambdoid suture between the parietal and occipital bones.

Two main fontanelles are identified on the newborn's head: the anterior fontanelle, which is diamond-shaped and bounded by the frontal and parietal bones, and the posterior fontanelle, which is triangular in shape and bounded by the occipital and parietal bones.

The anterior fontanelle is located at the intersection of the sagittal, frontal, and coronal sutures, whereas the posterior fontanelle lies at the intersection of the sagittal and lambdoid sutures. The following longitudinal dimensions of the fetal head are distinguished:

✵ suboccipito-bregmatic diameter — from the suboccipital depression to the anterior angle of the anterior fontanelle (length: 9.5 cm; circumference: 32 cm);

✵ suboccipito-frontal diameter — from the suboccipital depression to the hairline (length: 10 cm; circumference: 33 cm);

✵ occipito-frontal diameter — from the occipital protuberance to the glabella (length: 12 cm; circumference: 34 cm);

✵ mento-occipital diameter — from the chin to the most prominent part of the occiput (length: 13.5 cm; circumference: 38–42 cm);

✵ submento-bregmatic diameter — from the junction of the chin and neck to the center of the anterior fontanelle (length: 9.5 cm; circumference: 32 cm).

Additionally, two transverse dimensions of the head are measured: the biparietal diameter, measured between the furthest points of the parietal eminences (9–9.5 cm), and the bitemporal diameter, measured between the most distant points of the coronal suture (8 cm). Besides the dimensions of the fetal head, the measurements of its trunk (shoulder and pelvic girdles) are of great importance. The biacromial diameter of the newborn is measured between the acromion processes of the scapulae (12 cm; circumference: 35 cm); the bitrochanteric diameter is measured between the greater trochanters of the femurs (length: 9–9.5 cm; circumference is 28 cm in footling presentation, 32–34 cm in frank breech presentation, and 38–42 cm in complete breech presentation).

Signs of fetal maturity include:

✵ the umbilical ring located midway between the Pubic Symphysis and the xiphoid process;

✵ pale pink Skin color;

✵ well-developed subcutaneous adipose tissue;

✵ remnants of vernix caseosa present on the skin;

✵ lanugo Hair present only on the shoulders and upper back;

✵ scalp hair length of at least 2 cm;

✵ fingernails extending past the fingertips;

✵ firm and elastic ear and nasal cartilages;

✵ descended Testes in male infants;

✵ Labia Majora covering the Labia minora and Clitoris in female infants;

✵ body weight of 3200–3500 g;

✵ body length exceeding 47 cm.

Signs of vitality in a full-term newborn include active movements, a loud cry, open eyes, and a strong rooting and sucking reflex at the breast.