Physiological changes in pregnancy
Management of both healthy& diseased pregnancy necessitate knowledge
of the physiology of normal pregnancy. In early pregnancy, the
developing fetus, corpus luteum & placenta produce a lot off hormones
& substances that lead to many maternal local &systemic changes
including cardiovascular, respiratory &renal. most of these physiological
adaptation are completed during 1
st
trimester.
:
Volume homeostasis
1.maternal blood vol. expand during pregnancy start at 6-8 weeks of
pregnancy. There is increase in ECF(Plasma)>ICF& this account for 8-
10kg increase in maternal wt.
2. There is 6.5-8.5 increase in total body water by the end of pregnancy
3.increase in COP& renal blood flow
4. increase in plasma volume lead to haemodilution &physiological
anemia(decrease in Hb concentration & hematocrit.
5. decrease in plasma osmolality by 10 mOsmol/kg& there is decrease in
thirst threshold
6.decrease in osmotic & oncotic pressure(determined by albumin) by
20% , also there is increase in GFR& probably lead to development of
peripheral oedema
Factors lead to fluid retention : a. sodium retention b. decrease thirst
threshold c. decrease oncotic pressure.
Blood changes:
1.Decrease in maternal Hb due to increase in plasma volume by1000-
1500 ml compared to relative increase in erythrocyte mass by 280ml
2. decrease in mean red cell volume & s. ferritin
3. increase renal clearance of folic acid lead to decrease the level of
serum folate.
الدكتورة
سها وتوت
4. maternal platelet count remain constant , although it may be below than
non-pregnant due to increase aggregation.
Hemostasis & coagulation
Pregnancy is a hypercoaggulable state which return to normal around 4
weeks after delivery .
a. There is inc.in procoaggulant factors VII,VIII,IX,X.XII& fibrinogen by
50%.
b. level of von Will brand (carrier of factor 8) also increase.
c. anti-thrombin III remain unchanged, protein S activity decrease ,
increase in activated protein C resistance & there is increase in maternal
plasma D-diamer concentration& fibrin degradation product . those
increase in procoaggulant factors & decrease in fibrinolytic activity in
addition to venous stasis lead to increased incidence of thrombo- embolic
phenomena &DVT.
Biochemistry :
a. plasma protein con. decrease
b. serum creatinine ,uric acid &urea are reduced .
c. serum AL-Phosphatase increase due to placental production . s.
alanine transaminase &aspartate transaminase are decrease. LDH
slightly increase
system:
Immune
Pregnancy is considered is an immune suppressive state to allow
fetal allograft to implant & develop.
a. WBC increase up to 14x
10
9
/L
b. decrease in cytotoxic T cells, count of B-cell unaltered
Respiratory system :
a
.
-The vascularity of respiratory tract mucosa increase & the
nasal mucosa can be both edematous & prone to bleeding .
b
.
-The diaphragm is elevated by 4 cm as the pregnancy
progress& the lower ribcage circumference expand by 5cm
c
.
Pulmonary blood flow increase during pregnancy
d
.
-Tidal volume increase by 40% & respiratory rate remain
unchanged , this increase in the minute ventilation ( the
amount of air move in & out the lung /min) lead to
development of S.O.B in 60-70% of them ,vital volume
remain unchanged.
e
.
-The is decrease in functional residual capacity by 10-25%
which is a sum of expiratory reserve &residual volume
,both of which are decrease .
f
.
-There is increase in 2,3 DPG concentration in maternal
RBC this preferred binding to deoxygenated Hb, this
increase the availability of oxygen within the tissue &
more oxygen available to the fetus.
g
.
-There is increase in oxygen consumption during
pregnancy by 20%
h
.
-Progesterone has respiratory stimulant effect& then lead
to increase alveolar ventilation & tidal volume so there is
decrease in PCO2 by 15-20% & slight increase in PO2,
little change in PH & bicarbonate excretion is increase.
Cardiovascular system
-Elevation of diaphragm &increase in minute ventilation
lead to S.O.B
-Inc. in C.O.P by 40%due to increase in heart rate & stroke
volume by 10%
-increase in heart rate by 10-20 BPM& stoke volume by
10-20ml probably due to increase in plasma volume.
- decrease in diastolic B.P by 10-15 mmHg at first then
increase as in non-pregnant woman& decrease in mean
arterial pressure by 10%
- peripheral resistance decrease by 35%
-during pregnancy there is loud S1, audible S3 in 84% ,
ejection systolic murmur , diastolic murmur in 20%, 10%
develop continues murmur due to increase in mammary
blood flow.
GIT CHANGES:
-Pregnancy gingivitis is the term used for inflammation &
hyperplasia of the gingival mucosa occurring during
gestation which some time lead to gingival bleeding.
-elevated serum level of estrogen& progesterone lead to
increase vascular permeability& decrease immune
response lead to increase susceptibility to bacterial
colonization.
- change in salivary PH which become more acidic as well
as estrogen enhanced changes in the mucosa predispose to
dental caries.
-increase the incidence of reflux esophagitis& heartburn in
about 80% of woman due to increase progesterone which
lead to decrease lower esophageal sphincter tone &
increase placental production of gastrin.
-enlarged uterus &increase progesterone level lead to delay
gastric empty lead to development of constipation .
- increase placental production of estrogen & progesterone
that cannot metabolize by liver lead to development of
palmer erythema &telangiectasia in 60% of woman
- there increase in plasma level of cholesterol &
triglyceride.
Renal system:
-The kidney increase in size by 1-2cm
The is what we called hydro ureter& hydronephrosis which
marked at the right side together with alteration in the
urine composition itself predispose pregnant woman to
ascending UTI.
-GFR increase by 50%& renal blood flow increase by
80%.
-Due to increase GFR lead to decrease. level of blood urea
& serum creatinine
Increase GFR & decrease renal threshold for glucose lead
to development of glycosuria.
Reproductive organs
Changes in the uterus:
-Inc. in uterine blood flow by 40 fold with 80% of
blood distributed to intervillous space & 20% to uterine
myometrium.
-High level of estrogen &progesterone lead to both
hyperplasia &hypertrophy of myometrium that is lead
to increase in the weight of the uterus from 60g to
1000g during pregnancy.
-Uterine arteries undergo hypertrophy in the 1
st
half of
pregnancy. Progesterone helps maintain lower
myogenic tone in the uterine vessels despite of increase
in blood flow.
-As well as change in the size & no. of myometrial
cells, specialized cellular connection are also develop,
these facilitating the spread of membrane depolarization
& subsequent uterine contraction . these are apparent
initially as Braxton Hicks ,painless contraction that is
notice in the 2
nd
half of pregnancy.
Changes in the cervix:
-Because of increase vascularity & under the hormonal
effect ,the cervix become bluer in color ,soft &swollen.
also estrogen stimulate the growth of cervical columnar
epithelium This become more visible on the ectocervix
& called ectropion.
- Prostaglandin &collagenase lead to cervical
remodeling & softening.
Under the effect of estrogen, the vaginal epithelium
become more vascular &there is more desquamation
resulting into increase vaginal discharge . vaginal PH is
4.5-5 & this protected against ascending infection .
Breast & lactation:
-Estrogen lead to fat deposition around glandular tissue
& the no. of glandular ducts is increase
-Progesterone & HPL lead to increase no. of gland
alveoli - prolactin is essential for milk production &
secretion, it's level increase by 15 fold during
pregnancy
-Oxytocin is necessary for contraction of myoepithelial
cells surrounding the alveoli ,squeezing milk toward the
nipple.
Hormones produced within the pregnant uterus:
HCG, Hpl ,GnRH, CRH, prolactin ,GH, osterodiol,
progesterone, ACTH, insulin –like GF, PTH, renin&
angiotensin.
Thyroid function:
-HCG has thyrotrophic activity owing to alph-subunit
which is mimic to TSH, so TSH is suppressed during 1
st
trimester due to high HCG level
-Thyroid binding globulin increase. & reach the peak at 20
weeks ,this lead to increase in total T3,T4.
-As the GFR increase ,this lead to increase renal loss of
iodine & thus the development of goiter.
TSH is slightly suppressed in early pregnancy & free T4 is
decrease in late pregnancy.
-To assess TFT during pregnancy , we measure free
T3,T4& TSH but not total T3,T4.
Other metabolic changes :
-There is in the cortisol binding globulin& also increase in
unbound form.
-Also during pregnancy ,there is increase in the level of
ADH, aldosterone ,CRH, ACTH.
There is increase in basal metabolic rate ,increase wt. gain
during pregnancy as 1.6 kg/week gained during 1
st
trim.&
0.45kg/w in the 2
nd
trim. && 0.4 kg in the 3
rd
trim .with
total weight gain of 12.5 kg & mostly to increase in total
body water in addition to increase size of the uterus ,
placenta , developing fetus ,breast & AF.
-Blood level of fatty acid, triglyceride, cholesterol &
phospholipids are increase . estrogen & insulin resistance
are thought to be responsible .
-Total plasma calcium decrease as about 40% of calcium
bind to albumin& the latter is usually decrease during
pregnancy.& there is little change in unbound ionized
calcium. Also during pregnancy , there is increase in gut
absorption of calcium & decrease renal excretion&
mobilizing skeletal calcium , all these to preserve calcium
demand of the fetus . also level of parathyroid hormone
increase.
-Omega-fatty acid are essential & can obtained only from
the diet. It is essential for neural & retinal development as
it show to be associated with fetal cognitive &visual
development, prolong gestation &decrease preterm labor.
Skin changes :
- hyperpigmentation can be generalized or localized &
affect 90% of pregnant women like in the areola, nipple,
axilla& periumbilical area.
- Also development of linea nigra,
melisma(chloasma)which is symmetrical ,irregular macular
brown grey pigmentation of the face in 75% of women &
this is due to increase deposition of melanin due to
hormonal changes.
-Striae gravidarum (stretch marks) occur in 90% of
women& it is related to destruction of elastic fibers
depending on degree of abdominal distention, weight gain ,
genetic & hormonal factors .
There is increase in sebaceous activity , lead to
development of acne & hirsutism & thickening of scalp
hair fallowed by hair shedding postpartum because of
sudden hormonal changes after delivery.
References:
Obstetrics by Ten Teachers.