Physiological changes in pregnancy pdf - د. اشراق

Physiological

changes in

pregnancy

Dr. ISHRAQ MOHAMMED

Early pregnancy

In e arly pregnancy , the de veloping fe tus, corpus lute um

and place nta produce and re le ase increasing quantitie s of
hormone s, growth factors and othe r substances in to
maternal circulation which trigge rs a cascade of eve nts.

· C hange s in all body syste ms to pre pare the mothe r to

support fe tal growth

· F ollowing implantation, the mate rnal adaptation to

pre gnancy can be cate gorize d base d on following functions:

1. Incre ased availability of pre cursors for hormone production

and fe tal-placental me tabolism.

2.I mprove d transport capacity.

3.M aternal-fe tal e xchange .

4. Re moval of additional waste products.

Incre ased availability of me tabolic substrate s is achie ved by

incre ase s in die tary intake.

· T ransport capacity is enhanced by incre ase s in cardiac

output.

· T he place nta re gulate mate rnal-fe tal e xchange by 10-12

we eks ge station.

Disposal of waste product occurs through pe riphe ral

vasodilatation and by incre ases in ventilation and re nal
filtration.

Volume homeostasis

Maternal blood volume e xpand during pre gnancy to allow
ade quate perfusion of vital organs including the place nta
and fe tus, and to anticipate blood loss associate d with

de live ry.

· T he rapid e xpansion of blood volume be gins at 6-8 we e ks

ge station and plate aus at 32-34 we e ks gestation.

The most marke d e xpansion occurs in extracellular fluid
volume e spe cially circulating plasma volume , this

accounts for be twee n 8 and 10 kg of ave rage mate rnal
we ight gain during pre gnancy.

The factors contributing to fluid re tention are :

1.S odium re te ntion.

2.R e se tting of osmostat.

3.D e crease thirst thre shold.

4.D e crease plasma oncotic pressure.

· C onse que nce s of fluid re tention:

1.D e crease in hae moglobin conce ntration.

2.D e crease in hae matocrit.

3.D e crease in se rum albumin concentration.

4.I ncre asing in stroke volume .

5. Incre asing in re nal blood flow.

Blood

Haematology

· M aternal Hb le ve ls are de cre ases because of discre pancy

be twe e n incre ases in plasma volume &the incre ases in
e rythrcyte mass.

· T he me an Hb conce ntration falls from 13gm/ dl in non-

pre gnant state to10,9gm/ dl at 36 we eks of normal

pre gnancy.

· T he hae matocrit is also re duced 32-34pe r cent.

· P re gnancy without iron supple me ntation le ad to de pletion of

iron stores.

· R e nal cle arance of folic acid incre ase leads to fall in plasma

folate conc. Howe ve r re d ce ll folate conc. Do not fall to the
same e xte nt. Folate supple me ntation in wome n e ating

ade quate diet & carrying a single fetus is not routinely
indicate d.

· P late le t count may be lower than the non-pre gnant state

due to increase d aggre gation.

Erythrocyte sedime ntation rate is inre ase d in pre gnancy

Haemostasis &coagulation

Pre gnancy is a hype rgoagulable state & re turn to normal
around 4 wee ks afte r de live ry.

· A lmost all procoagulant factor including factor 7,8,9,10&11&

fibrinogen are incre ased during pregnancy

· F ibrinoge n is incre ase d by 50 pe r ce nt 300mg/ dl to

450mg/ dl in pre gnancy

· L e ve l of von Willebrand factor incre ase in pre gnancy

· T he incre ase in procoagulant, pote ntial for vascular damage

& incre ase ve nous stasis particularly in the lower
e xtre mitie s, e xplain why the incide nce of ve nous
thromboe mbolic complications is five time s gre ate r during
pre gnancy but this is to prote ct wome n from ble e ding afte r
de live ry

· A ctivate d prote in c re sistance is increase d in pregnancy

D-dime rs incre ase d in pre gnancy

Biochemistry

Plasma prote in conce ntration particularly albumin, are
de cre ased during normal pre gnancy , which not only affects

the plasma oncotic pre ssure , but also affe cts the pe ak
plasma conce ntration of drugs that are highly protein bound.

· S erum cre atinine, uric acid & ure a conce ntration are

re duce d during normal pre gnancy.

Alkaline phosphatase le vels incre ases thoughout pre gnancy.
In contrast SGOT & SGPT show lower leve l in uncomplicated
pre gnancy

The immune response

The pre se nce of the fetus is analogous to the grafting
of tissue s or organs be twe en two individuals of the
same spe cies who are gene tically dissimilar.

· P ropose d me chanisms for the succe ss of the fe tal

allograft:

1- mate rnal/ syste mic: none ( normal ce ll me diate d

immunity).

2-fe tal:

· a -ute rus & local lymphatic syste m:

· - uterus has bee n considered as privile ge d

immunological site.

· - localize d, non spe cific suppression induce s tole rance &

ge ne rate suppre ssor T cells.

· b -place nal:

· - se paration of the maternal-fe tal circulations, including

tight local barrie rs.

· - lack of e xpre ssion of class 2 HLA at the mate rnal-fe tal

inte rface.

· - limite d immune re sponse of cytotoxic T lymphocyte s

to trophoblasts.

c-syte mic : unidentifie d hume ral &ce llular
immunosuppre ssive elements.

The maternal brain & the senses

De cline in memory in the third trime ste r, the unde rlying

me chanisms are le ss cle ar. Proposed cause s include lack
of oe strogen or ele vate d leve l of oxytocin, which has an

amnesic e ffe ct while proge ste rone has a se dative e ffe ct.

· P re gnant wome n appe ar to have gre ate r tolerance for

pain, which is bioche mically me diate d by incre ase d se rum
le ve l of B-e ndorphins

· T HE SENSES

· C hange s in pe rce ption of odours during pre gnancy

,olfactory se nsitivity & odour thre sholds are significantly

de cre ased during the third trime ster.

Corneal se nsitivity decre ase s inmost pre gnant wome n &
this can be re late d to an incre ase in corne al thickne ss

cause d by oe dema & a de cre ase in te ar production
occurs in around 80 per ce nt of pre gnant wome n.

Respiratory tract

Airway: the ne ck, oropharynge al tissues, bre ast & che st wall
are all affe cte d by we ight gain, breast e ngorge me nt & air
way e dema, can compromise the airway le ading to difficulty
with visualization of the larynx during trache al intubation.

Ve ntilation: this begins to increase significantly at around 8
we eks ge station in re sponse to proge sterone se nsitization
of
the respiratory centre to CO2.the diaphragm is e levate d
4cm

by the enlarging uterus& the lowe r che st circumfe re nce

e xpand by 5cm.

· I ncre ase minute ventilation
· I ncre ase tidal volume
· D e crease re sidual volume

· D e crease d functional re sidual capacity
·

Vital capacity unchange d or slightly incre ase d

Oxyge nation: during pre gnancy the re is an increase in 2,3-

diphosphoglyce rate conce ntration within mate rnal
e rythrocyte s. This le ad incre ase availability of oxyge n within

the tissues(shifts the oxyge n-hemoglobin dissociation curve
to the right).

· D e crease d Pco2

· I ncre ased pO2

· P Halters little

· I ncre ased bicarbonate excre tion

Cardiovascular system

Sign & symptoms of pregnancy mimics those of he art
dise ase such as bre athle ssne ss, ede ma in the e xtre mitie s,
palpitation

are common & usually re present sinus tachycardia, which is

normal in pre gnancy.

· I n normal pre gnancy, cardiac output incre ase s as e arly as5

we eks ge stations

· N on pre gnant adult fe male 4.5L/ min

· 2 0we e ks pre gnant6.3L/ min 40pe r cent rise

· E arly labour17 pe r cent rise 7.3

· A ctive labor 7.7 L/ min

· 2

stage of labor 8.4

· M ost increase in cardiac output is contributed to raise of

stroke volume

De crease s in diastolic blood pre ssure are more marke d than
the de crease in systolic pre ssure le ad to increase in pulse
pre ssure . Late r, diastolic blood pre ssure increase s to le ve l

that are at le ast e quivale nt to those found in the non-
pre gnant state. The be st measure me nt are obtaine d when
the fifth Korotkoff sound is use d

A 70 pe r ce nt re duction in pe ripheral vascular resistance
has bee n de monstrated by 8 we eks ge station due to
alte ration in the production vasoconstrictor& vasodilator
age nt that pe ripheral arte rial tone .

· 1

heart sound is loud , wide splitting of the 2

heart sound,

he art sound is audible in 84 pe r ce nt of the pre gnant

wome n by 20 we eks ge station, an e jection systolic murmur
can be heard in 96 per ce nt of normal pregnant wome n,
diastolic murmur occur transie ntly in only 20 pe r ce nt of

pre gnant wome n &10 pe r cent de ve lop continuous murmur
due to increase d mammary blood flow.

Gastrointestinal changes

Oral: pre gnancy gingivitis, e de ma, hype rplasia & incre ased
ble eding of gingival tissue & dental caries &increase tooth
mobility.

· G ut: the ute rus displace the stomach & inte stine upwards,

incre ase incide nce of re flux oe sophagitis & he artburn,
de layed gastric e mptying.

Live r: physical finding such as te langie ctasia & palme r
e rythe ma, othe rwise sugge stive of live r dise ase in non-
pre gnant wome n, appe ar in up to 60e r ce nt of normal

pre gnancie s be cause of the hype roe strogenic state of
pre gnancy. Absolute he patic blood flow re main large ly
unalte red & he patic function remain normal.

The kidney & urinary tract

Incre ased kidne y size (1cm)

· D ilatation of re nal pe lvis & urete rs

· I ncre ase blood flow(60-75per ce nt)

· I ncre ase glome rular filtration (50pe r cent)

· I ncre ase renal plasma flow(50-80pe r cent)

· I ncre ase cle arance of most substance

· D e crease d plasma cre atinine , ure a& urate

Glycosuria is normal

Reproductive organ

Ute rus:

uterine

blood

flow

increase s

40-

folds(700ml/ minute at te rm)

· H igh le vels of mate rnal oe stradiol & proge sterone induce

hype rplasia &hype rtrophy of the myome trium incre asing
the we ight of the ute rus from 50-60gm prior to pre gnancy
to 1000gm by te rm.

By the third trime ste r, the uterus is de scribe d in lowe r &
upper segme nts. In addition to changes in the size
&numbe r of myome trial ce lls, interce llular gab junction
facilitating the spre ad of me mbrane de polarization &
subse quent myome trial contraction. The se are appare nt
initially as Braxton Hicks, painle ss contractions that are

notice in the 2

half of pre gnancy.

cervix: looks blue r during pre gnancy, swolle n &softer unde r
the influence of progeste rone & oe stradiol.

· V aginal e pithe lium be come s more vascular during

pre gnancy , & there is incre ased de squamation re sulting in

incre ase d vaginal discharge . This discharge has a more acid
pH& may prote ct against asce nding infe ction

Bre ast & lactation: the number of glandular duct is

incre ase d by oe srtoge n, while proge ste rone & human
place ntal lactoge n incre ase the numbe r of gland alve oli.

Endocrinology

Hormones produce d within pre gnant ute rus

1.P re gnancy spe cific: hCG& hPL

2.H ypothalamus: GnRH& CRH

3.P ituitary: prolactin, hGH, ACTH

4.S te roids: oe stradiol, progeste rone

5. Othe r pe ptide s: insuline like growth factor, parathyroid

hormone re late d pe ptide , re nin & angiote nsin 2

Pituitary gland

Enlarge d, conce ntration of prolactin 15 fold incre ase which is
ne ce ssary for initiation of lactation , it also may play a role in
the regulation of insulin secre tion.

· H uman growth hormone production by the ante rior pituitary

gland is suppre sse d during pre gnancy & human place ntal
lactoge n is involve d in suppressing its re lease .

Thyroid function

: mate rnal TSH production

suppresse d during the first trime ster but return to normal
afte r this. Thyroid binding globulin incre ase s in the first 2
we eks of pre gnancy & re ache s a plate au by 20 wee ks.
Incre ase re nal loss of iodide which result in e nlarge me nt of

the thyroid gland during pregnancy.

Uterus & placenta

HCG produced by the trophoblast ce lls, the B-subunit is
pre gnancy spe cific & used as a se nsitive pregnancy te st ,
this hormone has a major role during early pregnancy in
maintaining the function of corpus lute um, which produce s
proge ste rone .

Sex ste roid hormones are produce d in large quantitie s by

the

place nta

& fe tus. Oestroge n encourage s

ce llular

hype rtrophy of the

myome trium

while

progeste rone

discourage s contraction &, togethe r with prolactin, on the
tissue s of breast.

Corticosteroids

progre ssive

incre ase

mate rnal

circulating

concentrations of cortisol throughout normal pre gnancy has

be en notice as e arly as 11we eks & re aches 2-3fold highe r

concentration than in the non-pre gnant. Much of cortisol is
bound

cortisol-binding

globulin,

which

doubles

concentration during pre gnancy, but the re is also a slight
incre ase in unbound cortisol.

· A ldoste rone incre ase ten-fold in pregnancy.

The incre ased production of angiote nsins is the re sult of

incre ase production of the e nzyme re nin & its substrate
angiotensinogen

Corticotrophin-rele asing hormone (CRH) is produced by the
place nta in the se cond half of pre gnancy, which stimulate
the fe tal adrenal to synthe size & re lease

dihydroepiandroste rone , which the placenta the n converts to
oe stroge n. It also stimulate the fe tal adrenal gland to
synthe size & re le ase cortisol.

CRH pe ak leve l 48hours be fore de live ry . The placental
re gulation of its own me tabolism through e ffe ct on the fe tus,
with subseque nt e ffe cts on mate rnal ute rine physiology, &
possibly the onse t of labor, has be e n calle d the place ntal
clock the ory.

Metabolism

Energy re quire me nts & we ight gain

· C arbohydrate metabolism

· L ipid me tabolism

· C alcium meabolism