Physiological changes in pregnancy

Dr.M.Mirzaei Assistant professor of GynAmiralmomenin Hospital

The major maternal physiological adaptation to pregnancy

1-Reproductive organs.2-Systemic changes:

A. -volume homeostasisB. -bloodC. -cardio vascular system

3-Respiratory changes.4-urinary tract and renal function.5-Alimentary tract.6-endocrinological changes.

Reproductive organsA. the uterus:• Uterus

– Nonpregnant: 70gm, 10ml– Term: 1100gm, 5L– Dextrorotation (rectosigmoid on left side)

– Uteroplacental flow: 450~650ml/min (term).the ratio of muscle to connective tissue

increase from the lower part of the uterus to the fundus.

in early pregnancy uterine growth result from both hyperplasia and hypertrophy while later hypertrophy accounts for most of increase.

it weight one kilo gram at term( in pre pregnancy 70 grams)

as the pregnancy advanced the uterus divided into upper and lower uterine segment the lower uterine segment composed of lower part of uterus and the upper cervix composed mainly from connective tissue because of this the lower uterine segment becomes stretched in late pregnancy.

B.the cervix:• the cervix becomes softer and swollen in pregnancy

with the result columnar epithelium lining cervical canal becomes exposed to vaginal secretion.

• oestradiol stimulate growth of columnar epithelial of the cervical canal so it becomes violte and is called ectropine.

• the mucus gland becomes distended and secrete mucus which forms a mucus plug that is expelled in labour as the show.

• prostaglandins and collagenase especially in last weeks of pregnancy act on collagen fiber make cervix more softer.

E- Ovary

– Corpus luteum (first 7 weeks)– Pregnancy luteoma– Theca-lutein cysts

C. the vagina :• the vaginal mucosa becomes thicker during

pregnancy. • the vaginal discharge during pregnancy increased

due to increase desquamation of the superficial vaginal mucosal cells

skin signs:– linear nigra.– stria gravidarum.– chloasma.– Spider angioma, palmar erythema

Skin : • Striae gravidarum

• Linea nigra

• Chloasma

• Spider angioma, palmar erythema (estrogen)

breasts signs:• enlargement and increase pigmentation of the nipple.• increased pigmentation in the areola (areola).• formation of secondary areola.• montgomery areola or tubercle:• small tubercles 12-20 at the periphery of primary areola

appear at 8th week due to active sebaceous gland.• prominent vein on the surface.• colostrum at 16th week is reliable in primigravida.

D-breasts and lactation :• the earliest changes is a swelling of the breast tissue.

oestrogen leads to increase in number of glandular ducts.progesterone leads to proliferation of glandular epithelium of the

alveoli.prolactine leads to active secretion of milk after birth.

Most of the normal increase in weight during pregnancy is attributableto:

the uterus and its contents the breasts and increases in blood volume and extravascular extracellular fluid. A smaller fraction of the increased weight is the result of metabolic alterations that result in an increase in cellular water and deposition of new fat and protein—so-called maternal reserves.

Weight Gain (average 12.5kg)

Water Metabolism

• Increased water retension• Osmolality decrease 10

mOsm/kg• Extra water gain: 6.5 L

Systemic changes :

A. volume homeostasis:• the total blood volume is increased during

pregnancy 40_ 50 %• the most marked expansion occurs in extra

cellular volume (ECV) with some increase in intra cellular water.

The factors contributing including:Increase sodium retention.Decrease in plasma osmotic pressure.Decrease in thirst threshold.Resetting of osmostate.Decrease in plasma oncotic pressure.

Blood Volume

• Increase 40~45%• Mild anemia, but should not below 11 g/dl

B. Blood: The marked increase in plasma volume associated with

normal pregnancy causes dilution of many circulating factors.

* Hematological changes :

Decrease in:o red cell count.o hemoglobin concentration.o haematocrit.o plasma folate concentration.

Increase in :o white cell count.o erythrocyte segmentation rate .o fibrogen concentration.

Iron Metabolism

• Of the approximate 1000 mg of iron required for normal pregnancy; about 300 mg are actively transferred to the fetus and placenta, and another 200 mg are lost through various normal routes of excretion, primarily the

gastrointestinal tract. These are obligatory losses and occur even when the mother is iron deficient. The average increase in the total volume of circulating erythrocytes— about 450 mL—requires

another 500 mg because 1 mL of erythrocytes contains 1.1 mg of iron.

* Because most iron is used during the latter half of pregnancy, the iron requirement becomes large after midpregnancy and averages 6 to 7 mg/day.

• The total iron content (Storage) of ; normal adult women ranges from 2.0 to 2.5 g or about half the amount found normally in men. Importantly, the iron stores of normal young women are only approximately 300 mg.

• Activated state; During normal pregnancy, both coagulation and fibrinolysis are augmented but remain balanced to maintain hemostasis. They are even more enhanced in multifetal gestation.

• Fibrinogen: 300 mg/dl 450 mg/dl• D-dimer increase• Platelet decrease due to hemodilution

– Define thrombocytopenia: < 116,000

Coagulation and Fibrinolysis

C. Cardio vascular changes:

Earliest changes is periphral vasodilatationResults in decreased systemic vascular resistence

• heart rate increase (10-20%).• stroke volume increase (10%).• cardiac out put increase (30-50%).• Mean arterial blood pressure decrease (10%).-• Peripheral resistance decrease (35%).-

*normal changes in heart sounds during pregnancy:

• increase loudness S1 • >95% develop systolic murmur which disappears after

delivery.• 20% have a transient diastolic murmur.• 10% develop continues murmur due to increase

mammary blood flow.

Respiratory changes

↑tidal volume with normal (unchanged) respiratory rate.↑po2 and ↓pco2 with compensatory ↓HCO3(mild

compensated respiratory alkalosis).Breathlessness due to hyperventilation and elevation

of diaphragm. oxygen availability to placenta improves.PH alters little.

• ventilatory changes:thoracic anatomy changes.tidal volume increases(↓ Hering–Breuer inflation reflex).

vital capacity Unchanged.functional residual capacity decrease.

Lung compliance is unaffected by pregnancy, but airway conductance is increased and total pulmonary resistance reduced, possibly as a result of Progesterone.

The urinary tract and renal function

• blood flow increase (60-70%).• glomerular filtration increased (50%).• clearance of most substances is enhanced.• plasma creatinine ,urea,urate are reduced.• glycoseuria is normal.

Alimentary system changes

• the gums becomes spongy.

• the lower oesophageal sphincter is relaxed (hurt burn).

• gastric secretion is reduced.• the intestinal musculature is relaxed

(constipation).

Endocrinological changes:• prolactine concentration increases markedly

but act after delivery.• human growth hormone is suppressed .• insulin resistance develop.• thyroid function changes little.• trans placental calcium transport is enhanced.• corticosteroid concentration increased.• aldesterone concentration increased.

angiotensin and renine increased

– constant level of HCG in late pregnancy is useful in:

• controlling placental secretion of Estrogen progesterone.

• suppressing maternal immune system against fetus.

– the human chorionic gonadotrophine normally disappear from urine 7-10 days after delivery of placenta.

human placental lactogen• it is secreted by syncytotrophoblast.• It is level increase when the level of HCG start to

drop .• HPL has no effect on fetus.• HPL effect on :

1-the breast:o mammary growth during pregnancy.o produce of colostrums.o milk production lactation.

2-protiens:o HPL stimulate protein synthesis at cellular level.

3-carbohydrate:o stimulate insuline secretion .o inhibit insulin action.

4-fat: HPL mobilize fat from body store (lypolysis) lead

to increase maternal blood glucose and maternal tissue can not utilze the glucose so the glucose will be available for fetus.

Role of hPL during pregnancyRole of hPL during pregnancy

Growth hormone (GH and PRL-like effects) :

– induces lypolysis, plasma FFA

– inhibits glucose uptake and gluconeogenesis, glucose intolerance – insulinogenic effect ( insulin)– hyperinsulinemia– plasma IGF-I

progesterone

• it is production same as estrogen.• it has effect on smooth muscle leads to

decrease muscle excitability leads to muscle relaxation mainly in uterus.

Thyroid function

• increase thyroid binding globulin.• increase bound form of T3,T4.• no change in free form of T3,T4.So no evidence to support what previously

thought to be physiological such as increase in size of thyroid gland , increase BMR, body temperature, heart rate.

Maternal changes include : marked and early increase in hepatic production of thyroxine-binding globulin (TBG) increases serum thyroxine (T4) concentrations,

placental production of chorionic gonadotropin (hCG) has thyrotropinlike activity and stimulates maternal T4 secretion transient hCG-induced increase in serum T4 levels inhibits maternal secretion of thyrotropin.

Except for minimally increased free T4 levelswhen hCG peaks, these levels are essentially unchanged. (T3 triiodothyronine.)

Relative changes in maternal thyroid function during pregnancy :

2- Ultrasonography:

• 4 weeks: pregnancy sac with decidual reaction .

• 5 weeks: yolk sac.• 6 weeks: fetal echo.• 6-7 weeks : presence of fetal heart.• 9 weeks :fetal morphology.

First-trimester Milestones• 5 weeks: Gestational sac (~5mm)

seen with TVUS• 6 wks: Embryo (1-2mm) visible on

TVUS• Yolk sac: Seen with TVUS when

GS>10mm (>20 w/ TAUS)• Cardiac activity: Seen with TVUS

when GS >18mm (>25mm on TAUS)– Cardiac activity should always be

seen when embryo >5mm– Embryonic demise rate decreases

to 0.5% with visualization of cardiac activity in 6-10mm embryo

Normal gestational sac at arrow, endometrial cavity at curved arrow

“Double decidual sac” sign

GS=gestational sac, DP=decidua parietalis, * = endometrial cavity, arrow=decidua capsularis

Normal US Findings

Yolk sac (at arrow) within gestational sac Yolk sac (at curved arrow) with embryo (between X’s)

Normal US Findings

Embryo (black arrow); amnion (small arrow) does not fuse with chorion (large arrow) until 12-16wks gestation.

Spontaneous Abortion

Anembryonic pregnancy: large (>18mm) gestational sac without embryo

• Presentation: Varies greatly depending on type of abortion, but often presents with vaginal bleeding and uterine cramps or back pain.

• β-hCG: Falling or rising abnormally slow

• US findings vary depending on classification and cause of abortion

Abnormal US Findings: Spontaneous Abortion

Abortion in progress: low-lying gestational sac (thick arrow), decidual reaction and hemorrhage (mixed hyper- and hypo-echoic material between arrowheads)

Missed abortion: embryo (at arrow) is relatively small compared to large gestational sac. No cardiac activity was present.

Abnormal US Findings: Spontaneous Abortion

Patient presented with continued vaginal bleeding after spontaneous abortion. US shows retained products of conception.

Abnormally shaped gestational sac at 5 wks. Patient later had a complete spontaneous abortion.

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CRL-Uterine texture subtleitis and 1st trimester fetus

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