Chapter%207%20The%20fetus

1
Chapter 7The fetus

• By
• DR. Areefa Albahri
• Assistant Prof. of MCH
• Islamic University of Gaza

2
Introduction

• 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.

3
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.

4
(No Transcript)
5
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. .
6

• 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.

7

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

8

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

9
1620 weeks

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

10

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

11

• 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.

12

• 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.

13

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

14
(No Transcript)
15
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
  cord.

16
The fetal circulation takes the following
course

• 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
  development.

17
(No Transcript)
18
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.

19
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.

20

• 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

21
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
  born.

22
(No Transcript)
23
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
  neck.

24
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
  protuberance.
• The two parietal bones lie on either side of the
  skull. The ossification centre of each is called
  the parietal eminence.

25

• 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.

26
Sutures and fontanelles
27
(No Transcript)
28
Fetal skull landmarks
29
diameters of the fetal skull
30

• SOB, sub-occipitobregmatic 9.5
• SOF, sub-occipitofrontal 10.0
• OF, occipitofrontal
  11.5
• MV, mentovertical
  13.5
• SMV, sub-mentovertical 11.5
• SMB, sub-mentobregmatic 9.5

31

• 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

32

• 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
  glabella

33

• 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

34
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

35
(No Transcript)
36
(No Transcript)
37

• 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
  position.

38

• 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
  unlikely.

39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
Moulding

• 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
  sutures.

52
Moulding

• 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.

53
(No Transcript)
54
(No Transcript)
55
(No Transcript)
56
(No Transcript)