physiological changes during pregnancy

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 1st trimester.
Volume homeostasis:
1.maternal blood vol. expand during preg. 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.dec.thirst threshold c. dec. 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. dec. in mean red cell volume & s. ferritin
3. inc .renal clearance of folic acid lead to dec. the level of serum folate.
4. maternal platelet count remain constant , although it may be below than non-pregnant due to inc. 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 Willebrand (carrier of factor 8) also increase.
c. anti thrombin III remain unchanged, protein S activity dec. , 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 increase incidence of thrombo embolic phenomena &DVT.
Biochemistry :
a.plasma protein con. decrease
b.serum creatinine,uric acid &urea are reduced .
c. serum AL-Phophatase increase due to placental production . s. alanine transaminase &aspartate transaminase are dec.. LDH slightly inc.
Immune system:
Pregnancy is considered is an immune suppressive state to allow fetal allograft to implant & develop.
a.WBC inc up to 14x109/L
b. decrease in cytotoxic T cells, count of B-cell unaltered
Respiratory system :
a. -The vascularity of respiratory tract mucosa inc. & 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 inc. 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 inc. 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 preg. By 20%
h. -Progesterone has respiratory stimulant effect& then lead to inc. alveolar ventilation & tidal volume so there is dec in PCO2 by 15-20% & slight increase in PO2, little change in PH & bicarbonate excretion is increase.

Cardiovascular system
-Elevation of diaphragm &inc. in minute ventilation lead to S.O.B
-Inc. in C.O.P by 40%due to inc. in heart rate & stroke volume by 10%
-inc. in heart rate by 10-20 BPM& stoke volume by 10-20ml probably due to increase in plasma volume.
- dec. in diastolic B.P by 10-15 mmHg at first then increase as in non pregnant woman& dec in mean arterial pressure by 10%
- peripheral resistance dec. 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& dec. 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.
-inc. the incidence of reflux esophagitis& heartburn in about 80% of woman due to inc. progesterone which lead to dec. lower esophageal sphincter tone & increase placental production of gastrin.
-enlarged uterus &inc. progesterone level lead to delay gastric empty lead to development of constipation .
- inc. placental production of estrogen & progesterone that can not metabolize by liver lead to development of palmer erythema &telangiectasia in 60% of woman
- there inc. in plasma level of cholesterol & triglyceride.

Renal system:
-The kidney inc. 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 inc. by 50%& renal blood flow inc. by 80%.
-Due to inc. 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 inc. in the weight of the uterus from 60g to 1000g during pregnancy.
-Uterine arteries undergo hypertrophy in the 1st half of pregnancy. Progesterone helps maintain lower myogenic tone in the uterine vessels despite of inc. 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 2nd half of pregnancy.
Changes in the cervix:
-Because of inc. vascularity & under the hormonal effect ,the cervix become bluer in color ,soft &swollen. also estrogen stimulate the growth of cervical columnar ep. 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 inc.
-Progesterone & HPL lead to inc. no. of gland alveoli - prolactin is essential for milk production & secretion, it s level inc 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 –likeGF, PTH, renin& angiotensin.

Thyroid function:
-HCG has thyrotrophic activity owing to alph-subunit which is mimic to TSH, so TSH is suppressed during 1st trimester due to high HCG level
-Thyroid binding globulin inc. & reach the peak at 20 weeks ,this lead to inc. in total T3,T4.
-As the GFR inc. ,this lead to inc renal loss of iodine & thus the development of goiter.
TSH is slightly suppressed in early pregnancy & free T4 is dec. 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 inc. in unbound form.
-Also during pregnancy ,there is inc. in the level of ADH, aldosterone ,CRH, ACTH.
There is increase in basal metabolic rate ,inc. wt. gain during pregnancy as 1.6 kg/week gained during 1st trim.& 0.45kg/w in the 2nd trim. && 0.4 kg in the 3rd trim .with total weight gain of 12.5 kg & mostly to inc. in total body water in addition to inc . 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 dec. as about 40% of calcium bind to albumin& the later is usually dec. during pregnancy.& there is little change in unbound ionized calcium. Also during pregnancy , there is inc. 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 inc. 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.