physiology of pregnancy. the perinatal care of the fetus. prepared by n. bahniy

Physiology of pregnancy. The perinatal care of the fetus.

Prepared by N. Bahniy

STAGES OF PRENATAL DEVELOPMENT Preembryonic stage - first 2

weeks. Products of conception are called as conceptus.

Embryonic stage - from the third week until the end of the eight week. From this period conceptus is called embryo.

Fetal period starts from the beginning of the ninth week through the full 41 weeks of development. Products of conception are called as fetus.

Preembryonic Stage fertilization zygote formation division of fertilized ovum morula formatiom formation of free blastocyst implantation of the ovum in

the uterine wall Primitive chorionic villi

formation Initial folding into layers –

gastrulation beginning.

Chorion and amnion begin to form during this period also.

A SPERM FERTILIZING AN OVUM

Formation of free blastocyst

Morula

From outer layer - trophoblast

From inner layer - embryoblast

Implantation- attachment of the blastocyst on the 7th day into uterine wall

called implantation.

EMBRYONIC STAGE Formation of supportive structures - include the placenta, umbilical

cord, and certain extraembryonic membranes. The yolk sac forms early and manufactures blood cells until the liver

takes over at 6 week. The allantois forms the part of the yolk sac; it produces blood cells and

eventually forms the umbilical arteries and veins. During the third week the primitive streak appears, and then, other

rudiments of organs form, including the central nervous system, notochord, neural tube, heart, limbs, finger, toes, eyes, ears, and nose.

AN AMBRYO IS ABOUT 5 WEEKS OLD

"FETUS OF ABOUT EIGHT WEEKS, ENCLOSED IN THE AMNION,"

FROM GRAY'S ANATOMY. PART OF THE PLACENTA IS SHOWN AS THE LOWEST FEATURE IN THIS IMAGE, AND THE AMNION EXTENDS

ABOVE THE FETUS.[1

Critical periods of fetal development

ImplantationMorphogenesis and organogenesisPlacentation

Growing and differentiation of the structures during the Fetal Period

Conceptus structure in the end of pregnancy

Fetus Umbilical cord Placenta Amniotic Fluid Amnion Chorion Decidua

Fetal characteristics

Classification Gestational age (weeks of

pregnancy

Weight, gram Length, cm Signs of maturity

“Deep pre-term fetus”

12 – 22 25 – 500 9 - 25 Absent

“Fetus pre-term” 22 –36+6 days 500 – 2500 25 - 46 Absent

“Fetus in-term” 37 – 41 > 2500(3200-3500)

47(50-52)

Present

“Fetus post-term” > 41 > 2500 47 Present

Signs of fetal maturity

Umbilical ring is between pubis and processes xyphoideus

Pink skin Well-developed subcutaneous tissue, Lanugo in the shoulders and upper part

of the back Length of the hair on the head is 2 cm Nails are present till the top of the fingers Well-developed ears and nose cartilage Testes are present in the scrotum in the

boys and labia major are covered labia minor in the girls

Active movements Loud cry of the infant

FETAL HEAD AT TERM

DIAMETERS OF THE FETAL HEAD AT TERM

1. The suboccipitobregmatic (9.5 cm, 32cm), which follows from the middle of the large fontanel to the undersurface of the occipital bone.

2. The suboccipitofrontalis (10cm,33 cm) – from subocipital fossa to border of the hair.

3. The occipitofrontal (12 cm, 34 cm), which follows a line extending from a point just above the root of the nose to the most prominent portion of the occipital bone.

4. The occipitomental (12.5-13 cm, 39-41cm), from the chin to the most prominent portion of the occiput.

5.The sublingquobregmatica (9,5 cm, 32 cm).

6. The biparietal (9.5 cm), the greatest transverse diameter of the head, which extends from one parietal boss to the other.

7. The bitemporal (8.0 cm), the greatest distance between the two temporal sutures.

DIAMETERS OF THE FETAL BODY AT TERM

Biacromial distance – 12cm, 34-35 cm

Bisiliacus distance – 9cm, 27-28 cm

DECIDUA - MATERNAL MEMBRANE, immunologically specialized tissue.

provides for embryo-fetal nutrition.

Fetal membranes

Structure

chorion and amnion Amnion

A double-layered

translucent membrane

Become distended

with fluid

Amniotic fluid 1000-1500ml at 36th-38th week (peak) Absorb

1. Fetal membrane

2. Umbilical cord

3. Fetal skin

4. Fetal drinking

Source

1. Fetal urine

2. Fetal lung

3. Exudation of amnion and fetal skin

Functions:

Protection of the fetus

Protect mother, prevent infection

Formation of the forebag

Umbilical Cord

Structure

amnion, yolk sac, one vein, two artery and Wharton jelly

Length

30-70cm

Placenta at section

Fetal and maternal parts.

Cotyledon –

is a small

compound of placenta.

Placental villi

At term, the placenta contains approximately 12 m2 of villous surface area for maternofetal exchange.

Placental functions

Endocrine Transfer of nutrients Excretory - removal

of the products of fetal catabolism

Barrier Oxygen-transport

Placental hormones1. Protein hormones of the placenta: chorionic gonadotropin (cHG)– it is maintain the function of the corpus

luteum during early gestation, promote uterine vascular vasodilation and myometrial smooth muscle relaxation, relaxin secretion by the corpus luteum, stimulate thyroid activity, and some more basic forms also stimulate iodine uptake

human lactogen – its actions include lipolisis and an increase in the levels of circulating free fatty acids, thus providing a source of energy for maternal metabolism and fetal nutrition

2. Steroid hormones of the placenta: estrogens; progesterone.3. Chorionic adrenocorticotropin and thyrotropin, growth hormone

variant, parathyroid hormone-related protein (PTH-rP), calcitonin, and relaxin – no significant role has been established for this substance in normal human pregnancy.

4. Hypothalamic-like-releasing hormones of the placenta

Type of human placentation - hemochorioendothelial

Role of Estrogen in Pregnancy:

Increasing blood flow to the uterus by promoting vasodilation.

Changing the sensitivity of the respiratory system to carbon dioxide.

Softening of the cervix, initiating uterine activity, and maintaining labor.

Developing the breasts in preparation for lactation and secretion of prolactin by the pituitary gland.

Role of Progesterone in Pregnancy:

Ready the uterus for implantation. Relaxes smooth muscle to prevent

spontaneous abortion. Works to prevent a maternal immunologic

response to the fetus. Relaxes smooth muscle

– to decrease motility & improve absorption of nutrients.

– Enlarges the ureters & bladder to increase capacity.

Plays a role in development of the alveoli & ductal system to prepare for lactation.

Physiologic changes in pregnant woman

Genital organs1. Uterus1) capacity: 5ml-5000ml.weight: 50g-

1000g2) Hypertrophy of muscle cells3) Endometrium→decidua: basal

decidua, capsular decidua, true decidua

4) Contraction: Braxton Hicks5) Isthmus uteri: 1cm→ 7-10cm6) Cervix: colored7) Ovary: placenta replaces ovary

(10th week)8) Vagina: dilated and soft, pH↓(anti-

bacteria)9) Ligaments: relaxed

Physiologic changes in pregnant woman

Cardiovascular system1. Heart: move upward, hypertrophy of cardiac muscle2. Cardiac Output increase by 30%, reach to peak at 32nd –

34th week3. Blood pressure early or mid pregnancy Bp↓.late pregnancy

Bp↑ .Supine hypotensive syndrome

Physiologic changes in pregnant woman

Hematology1. Blood volume1) Increase by 30%-45% at 32nd –34th (peak)2) Relatively diluted2. Composition1) Red cells Hb:130→110g/L, HCT:38%→ 31%.2) White cells: slightly increase3) Coagulating power of blood: ↑ 4) Albumin: ↓,35 g/L

Physiologic changes in pregnant woman

The Respiratory system

1. R rate: slightly ↑2. vital capacity: no

change

3. Tidal volume: ↑ 40%

4. Functional residual capacity:↓

5. O2 consumption: ↑ 20%

Physiologic changes in pregnant woman

1. Kidney

1) Renal plasma flow (RFP):↑35%

2) Glomerular filtration rate (GFR):↑ 50%

2. Ureter

Dilated (P↑)

3. Bladder

Frequent urination

Physiologic changes in pregnant woman

Gastrointestinal system

1) Gastric emptying time is prolonged→ nausea.

2) The motility of large bowel is diminished → constipation

3) Liver function: unchanged

Physiologic changes in pregnant woman

Endocrine1. Pituitary (hypertrophy)1) LH/FSH: ↓2) PRL:↑3) TSH and ACTH:↑2. Thyroid1) enlarged (TSH and HCG↑)

2) thyroxine↑ and TBG↑ → free T3 T4 unchanged