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Chapter 7 The fetus


CHAPTER 7 THE FETUS By DR. Areefa Albahri Assistant Prof. of MCH Islamic University of Gaza DR. Areefa Albahri – PowerPoint PPT presentation

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Title: Chapter 7 The fetus

Chapter 7The fetus
  • By
  • DR. Areefa Albahri
  • Assistant Prof. of MCH
  • Islamic University of Gaza

  • The midwife's role in embryological and fetal
    development is focused on health education for
    maternal and fetal well-being. This involves
    providing parents with information about the
    effects of maternal lifestyle, such as diet,
    smoking, alcohol, drugs and exercise, on fetal
    growth and development. Additionally, an
    understanding of fetal development is of value
    when a baby is born before term.

Time scale of development
  • Embryological development is complex and occurs
    from weeks 28 and includes the development of
    the zygote in the first 23 weeks after
    fertilization. Fetal development occurs from week
    8 until birth. The interval from the beginning of
    the last menstrual period (LMP) until
    fertilization is not part of pregnancy. However,
    this period is important for the calculation of
    the expected date of birth.

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Summary of embryological and fetal development
embryo 04 weeks Primitive streak appears
Blastocyct implantation Primitive central
nervous system forms Heart develops and begins
to beat Covered with a layer of skin Limb buds
form Gender determined. .
  • 48 weeks
  • Very rapid cell division
  • Blood is pumped around the vessels
  • Lower respiratory system begins
  • Head and facial features develop
  • Early movements
  • Visible on ultrasound from 6 weeks.

  • Fetus
  • 812 weeks
  • Rapid weight gain
  • Eyelids fuse
  • Urine passed
  • Swallowing begins
  • External genitalia present but-gender not
  • Fingernails develop
  • Some primitive reflexes present.

  • 1216 weeks
  • Rapid skeletal development
  • lanugo appear
  • Meconium present in gut
  • Nasal septum and palate fuse
  • Gender distinguishable.
  • Able to suck

1620 weeks
  • Constant weight gain
  • Quickening
  • Fetal heart heard on auscultation
  • Vernix caseosa appears
  • Skin cells begin to be renewed.

  • 2024 weeks
  • Most organs functioning well
  • Eyes complete
  • Periods of sleep and activity
  • Ear apparatus developing
  • Responds to sound
  • Skin red and wrinkled.

  • 2832 weeks
  • Begins to store fat and iron
  • Testes descend into scrotum
  • Lanugo disappear from face
  • Skin becomes paler and less wrinkled.
  • 2428 weeks
  • survival may be expected if born
  • Eyelids open
  • Respiratory movements.

  • 3236 weeks
  • Weight gain 25 g/day
  • Increased fat makes the body more rounded
  • Lanugo disappears from body
  • Nails reach tips of fingers
  • Ear cartilage soft
  • Plantar creases visible.

  • 36 weeksBirth
  • Birth is expected
  • Shape rounded
  • Skull formed but soft and pliable.

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The fetal circulation
  • The placenta is the source of oxygenation,
    nutrition and elimination of waste for the fetus.
  • The ductus venosus which connects the umbilical
    vein to the inferior vena cava
  • The foramen ovale which is an opening between the
    right and left atria
  • The ductus arteriosus which leads from the
    pulmonary artery to the descending aorta
  • The hypogastric arteries which branch off from
    the internal iliac arteries and become the
    umbilical arteries when they enter the umbilical

The fetal circulation takes the following
  • Oxygenated blood from the placenta travels to the
    fetus in the umbilical vein. The umbilical veins
    divide into the portal vein in the liver, the
    ductus venosus joining the inferior vena cava.
    Most of the oxygenated blood that enters the
    right atrium passes across the foramen ovale to
    the left atrium and the left ventricle, and then
    the aorta. The head and upper extremities receive
    approximately 50 of this blood via the coronary
    and carotid arteries, and the subclavian arteries
    respectively. The rest of the blood travels down
    the descending aorta. A little blood travels to
    the lungs in the pulmonary artery, for their

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Adaptation to extrauterine life
  • At birth, there is a dramatic alteration to the
    fetal circulation and an almost immediate change
    occurs. The cessation of umbilical blood flow
    causes a cessation of flow in the ductus venosus,
    a fall in pressure in the right atrium and
    closure of the foramen ovale. As the baby takes
    the first breath, the lungs inflate, and there is
    a rapid fall in pulmonary vascular resistance.

Adaptation to extrauterine life
  • The ductus arteriosus constricts due to
    bradykinin released from the lungs on initial
    inflation. The effect of bradykinin is dependant
    on the increase in arterial oxygen. In the term
    baby, the ductus arteriosus closes within the
    first few days of birth.

  • These structural changes become permanent and
    become as follows
  • The umbilical vein becomes the ligamentum teres
  • The ductus venosus becomes the ligamentum venosum
  • The ductus arteriosus becomes the ligamentum
  • The foramen ovale becomes the fossa ovalis

The fetal skull
  • The fetal head is large in relation to the fetal
    body compared with the adult . Additionally, it
    is large in comparison with the maternal pelvis
    and is the largest part of the fetal body to be

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Divisions of the fetal skull
  • The skull is divided into the vault, the base and
    the face. The base comprises bones that are
    firmly united to protect the vital centres in the
    medulla. The face is composed of 14 small bones
    which are also firmly united and
    non-compressible. The vault is the large,
    dome-shaped part above an imaginary line drawn
    between the orbital ridges and the nape of the

The bones of the vault
  • The occipital bone lies at the back of the head.
    Part of it contributes to the base of the skull
    as it contains the foramen magnum, which protects
    the spinal cord as it leaves the skull. The
    ossification centre is the occipital
  • The two parietal bones lie on either side of the
    skull. The ossification centre of each is called
    the parietal eminence.

  • The two frontal bones form the forehead or
    sinciput. The ossification centre of each is the
    frontal eminence. The frontal bones fuse into a
    single bone by 8 years of age.
  • The upper part of the temporal bone on both
    sides of the head forms part of the vault.

Sutures and fontanelles
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Fetal skull landmarks
diameters of the fetal skull
  • SOB, sub-occipitobregmatic 9.5
  • SOF, sub-occipitofrontal 10.0
  • OF, occipitofrontal
  • MV, mentovertical
  • SMV, sub-mentovertical 11.5
  • SMB, sub-mentobregmatic 9.5

  • The longitudinal diameters are
  • The sub-occipitobregmatic (SOB) diameter (9.5 cm)
    measured from below the occipital protuberance to
    the centre of the anterior fontanelle or bregma

  • The sub-occipitofrontal (SOF) diameter (10 cm)
    measured from below the occipital protuberance to
    the centre of the frontal suture
  • The occipitofrontal (OF) diameter (11.5 cm)
    measured from the occipital protuberance to the

  • The mentovertical (MV) diameter (13.5 cm)
    measured from the point of the chin to the
    highest point on the vertex, slightly nearer to
    the posterior than to the anterior fontanelle
  • The sub-mentovertical (SMV) diameter (11.5 cm)
    measured from the point where the chin joins the
    neck to the highest point on the vertex
  • The sub-mentobregmatic (SMB) diameter (9.5 cm)
    measured from the point where the chin joins the
    neck to the centre of the bregm

Presenting daimeters
  • Presenting diameters
  • Some presenting diameters are more favourable
    than others for easy passage through the pelvis
    and this will depend on the attitude of the head.
    This term attitude is used to describe the degree
    of flexion or extension of the head on the neck.
    The attitude of the head determines which
    diameters will present in labour and therefore
    influences the outcome.
  • There are always two, a longitudinal diameter and
    a transverse diameter. The presenting diameters
    determine the presentation of the fetal head, for
    which there are three

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  • Cephalic presentation come in three ways
  • Vertex presentation. When the head is well flexed
    the sub-occipitobregmatic diameter (9.5 cm) and
    the biparietal diameter (9.5 cm) present . As
    these two diameters are the same length the
    presenting area is circular, which is the most
    favourable shape for dilating the cervix and
    birth of the head. The diameter that distends the
    vaginal orifice is the sub-occipitofrontal
    diameter (10 cm).
  • When the head is deflexed, the presenting
    diameters are the occipitofrontal (11.5 cm) and
    the biparietal (9.5 cm). This situation often
    arises when the occiput is in a posterior

  • Face presentation. When the head is completely
    extended the presenting diameters are the
    sub-mentobregmatic (9.5 cm) .
  • The sub-mentovertical diameter (11.5 cm) will
    distend the vaginal orifice.
  • Brow presentation. When the head is partially
    extended and the mentovertical diameter (13.5 cm)
    and the bitemporal diameter (8.2 cm) present. If
    this presentation persists, vaginal birth is

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  • The term moulding is used to describe the change
    in shape of the fetal head that takes place
    during its passage through the birth canal.
    Alteration in shape is possible because the bones
    of the vault allow a slight degree of bending and
    the skull bones are able to override at the

  • This overriding allows a considerable reduction
    in the size of the presenting diameters.
    Additionally, moulding is a protective mechanism
    and prevents the fetal brain from being
    compressed as long as it is not excessive, too
    rapid or in an unfavourable direction.

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