Physiology of Pregnancy
Xing Aiyun
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
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