Physiology of Pregnancy

Xing Aiyun

aiyun-x@126.com

Ref:

1,Current Obstetric&Gynecologic

Diagnosis & Treatment （11ed）

2,Willams’ obstetrics(24ed)

Obstetrics

The branch of medicine that is concerned with

pregnancy, labor, and the puerperium in both

normal and abnormal circumstances.

maternal and neonatal outcome are used as an

index of the quality of health and life in a human

society.

Obstetrics

Pregnancy/labor/puerperium is a normal physiologic

event that may be dangerous for some ones.

The goal of modern obstetrics：identification and

special treatment of the high-risk patient, to ensure as

much as possible a good outcome both for mother and

her offspring

“I am going to fetch a new baby. The journey is dangerous and I may not return…”

Common saying of Tanzanian women to older children near the time of delivery.

Although health indicators overall have improved in most of the world Over the past 20 years, two critical indicators –

maternal mortality and newborn mortality have hardly changed.

The current MMR Tanzania is estimated at 1,100

/100,000 live births (compared to Canada to

6/100,000)

The beginning of pregnancy:

Fertilization of the ovum

The termination of pregnancy :

Discharge the fetus and its

appendage from the maternal

uterus

Physiology of Pregnancy

Introduction

Embryology

Fetal appendage (placenta、fetal

membranes 、 umbilical cord 、

amniotic fluid)

Maternal adaptation to

pregnancy

Fetal growth and development

prenantal care

Fertilization

The beginning of a new life.

Implantation：

➢ 6 days after fertilization.

➢ The blastocyst ( trophoblast invasion ) and

maternal endometrium (decidua) development must

occurs in parallel.

Infertility

Embryology

Placenta(The structure )

Fetal origin

Amnion

Chorion vills

(trophoblast cell)

Maternal originBasal decidua

Placenta ( function )

The fetus is a demanding and efficient parasite!

During its brief intrauterine passage, the fetus is dependent on

the placenta for pulmonary, hepatic, and renal functions

Metabolic function

Gas exchange: ( lung)Nutrient transfer: ( liver)Elimination of fetal metabolites：( kidney)`

Placenta ( function )

Defensive function (limited)

Endocrine function:

Syncytiotrophoblast

HCG、HPL、PAPP、E、P、HSAP、

Oxytocinase

Placenta ( The function )

HCG（Human Chorionic Gonadotropin ）

➢ A specific marker for pregnancy: normal and abnormal (abortion, ectopic, hydatidiform moles and choriocarcinoma). β- HCG

➢ Corpus luteum 黄体(ovary) → Corpus luteum of pregnancy

➢ Immunological mechanism on the maternal-fetal interface

Placenta ( function )

Steroid: Estrone、Progesterone

✓ Corpus luteum of pregnancy →placenta, 8∼10W

✓ Maternal -placental – Fetal unit

✓ Maintaining the pregnancy and maternal adaptation to

pregnancy

Fetal membrane

Chorion laeve (outer) 、amnion(inner)

avascular membranous structure

It has an initiating effect on the onset of labor.

Umbilical cord

Average length: 30-100 cm

Vessels: 2 arteries、1 vein

within Wharton’s jelly

It is an important passage

for fetal-maternal exchange

Amniotic fluid

Function:

protection of fetus

protection of mother

Amniotic fluid

Maternal adaptation to pregnancy

During normal pregnancy, virtually every organ system undergoes anatomical and functional changes, The physiological adaptations to pregnancy are profound. and most occur in response to physiological stimuli provided by the fetus and placenta

Affect from placental hormone (E,P)

Facilitate fetal development

Prepare for the process of labor

Maternal adaptation to pregnancy

Many of these physiological adaptations

Be perceived as abnormal in the

nonpregnant woman & misinterpreted as

pathological

Lead to unmask or worsen preexisting

disease.

Alter criteria for diagnosis and treatment of

diseases.

Uterine

During pregnancy the uterus has achieved

a capacity that is 500 to 1000 times greater

than in the nonpregnant state

nonpregnant term pregnant

Weight 70g 1100g

Volume ≤10ml 5L

Uterine

Stretching & hypertrophy of the

muscle cells

✓ The accommodation of a conceptus

✓ Prepare for labor

Marked increase in the number of

blood vessels

✓ Maternal-fetal exchange

Uterine endometrium→decidua

Isthmus uteri → low uterine segment

Uterine cervix

Cervical softening

✓ Maintenance of a pregnancy to term,

✓ Dilatation to aid delivery

Mucous Plug

✓ Rich in immunoglobulins and cytokines

✓ Act as an immunological barrier to protect the

uterine contents against infection from the vagina

Ovaries

Ovulation ceases & maturation of new follicles

suspended

Corpus luteum functions during the first 6 to 7

weeks of pregnancy—4 to 5 weeks

postovulation—and thereafter contributes

relatively little to progesterone production.

Vagina

preparation for the distention that accompanies

labor and delivery

✓ increase in mucosal thickness✓ loosening of the connective tissue

✓ hypertrophy of smooth muscle cells

Acidic pH: Result of increased production of lactic

acid from glycogen by the action of Lactobacillus

acidophilus

-- against infection from the vagina

Perineum

Increased vascularity and hyperemia

develop in the skin

Softening of the normally abundant connective tissue

Breasts

Increase in size, preparation

for lactation after birth

Endocrinology of lactation:

P、E、PL、PRL、cortisol、insulin

Hypervolemia40 -45 % above the nonpregnant blood volume after 32 ~ 34w

Haemodilutionmore plasma than erythrocytes anaemia : Hb＜100g/L

Hematological Changes

Haematological changes

WBC ↑:

15x109/L, 30w

Low-grade increase in coagulant activity:

Help reduce blood loss at delivery, increase

risk of thrombosis

Cardiovascular changes

The resting pulse rate

increases about 10 beats/min

during pregnancy

Arterial pressure decreases to

a nadir at 24 to 26 weeks and

rises thereafter. diastolic

pressure decreases more than

systolic

Supine hypotensive syndrome

Obstruction of the inferior

vena cava by uterine

Characterized by decreased

cardiac output , bradycardia

and hypotension

Relief is obtained with the

lateral position

Renal changes

Kidney size increases slightly

glomerular filtration rate (GFR) and renal

plasma flow( RPF ) increase ~50%

✓ Urinary frequency

✓ Plasma urea and creatinine ↓

✓ Glucosuria

Gastrointestinal tract

The stomach and intestines displaced, Consequently,

the physical findings in certain diseases are

altered. The appendix, for instance, is usually

displaced upward and somewhat laterally as the

uterus enlarges. At times, it may reach the right

flank.

Gastrointestinal tract

Gastric-emptying and intestinal transit times delayed,

Gastric reflux → heartburn

Gums become hyperemic and softened , bleed easily

epulis of pregnancy

-- highly vascular swelling of the gums

Embryo and fetal growth

Weeks from LMP Weeks stage of development

1~12,or first trimester 2 ~4 Fertilisation (pre-embryonic)

4 ~10 Embryonic development

(Organogenesis)

13 ~27,or second trimester Fetal development

23 onwards Viability

28 ~40,or third trimester Maturation

37 ~42,or term Delivery of the mature fetus

Cardiovascular system

Fetal circulation

Umbilical vein: well-oxygenated and nutrients-

riched

Umbilical arteries: inverse

Fetal blood: mixture with arterial and venous

blood.

Fetal circulation

The high pulmonary vascular resistance

right artrium → Left ( Foramen ovale)Pulmonary artery → Aorta (ductus arteriosus)

Cardiovascular system

After birth

Expansion of lung: pulmonary vascular resistance decrease

Foramen ovale、ductus arteriosus: collapse

Pulmonary System

Fetal gas exchange function is performed by placenta although there is structure and morphological fetal lung development in utero.

The presence of a sufficient amount of surface –active materials (surfactant) by lung type II cells is

of considerable importance to the newbornsurvival

Perinatal Medicine

Perinatal period

28 weeks of completed gestation to the

first 7 days of neonatal life (China)

The key span for fetal and neonatal life

Cooperation between obstetrician and

pediatrician

Perinatal mortality is a index of the healthy

level of a country

Prenatal care

“A comprehensive antepartum care program

involves a coordinated approach to medical care

and psychosocial support that optimally begins

before conception and extends throughout the

antepartum period”

--- ACOG 2007

Prenatal care

preconceptional care

prompt diagnosis of pregnancy

initial prenatal evaluation

follow-up prenatal visits

Decrease maternal and perinatal mortality

Decrease birth defect rate

Signs

amenorrhea

morning sickness

Symptoms

increase in uterine size (globular 、softer )

breast tenderness、hyperpigmented nipples

Assisted test

pregnancy tests: 8 ～ 9 days after ovulation

sonographic recognition of pregnancy

第五章 妊娠生理Diagnosis of Pregnancy

--1st trimester

Diagnosis of late Pregnancy

Enlargement of uterus

第五章 妊娠生理

Palpation of fetal body

Perception of Fetal Movements

Primigravida: 18 ～20 weeks

Mulitigravida: 16 ～18 weeks

第五章 妊娠生理

Sonographic diagnosis

late pregnancy

第五章 妊娠生理

Fetal size、position

Fetal movement

Fetal heart beat

Fetal structure

Preconceptional prevention

Prenatal screening & diagnosis

Newborn screening

Prevention of birth defects

(3 levels)

Thank you