Anatomical and physiological changes in pregnancy Anatomical & physiological Changes of pregnancy

The anatomical, endocrinological and physiological changes are a positive adaptation of the mother to accommodate and support the fetus as it grows and develops throughout gestation. At the same time the mother is prepared for the delivery of the fetus and lactation. The physiological changes in the mother commence very early in pregnancy and precede any possible need of the fetus.

Reproductive organs Uterus High level of maternal oestradiol and progesterone stimulate both hyperplasia and hypertrophy of the myometrial cells, increasing the weight of the uterus from 50 – 60g prior to pregnancy to 1000g by term.

The uterus A specialized cell connection also develop with increasing gestation these allow changes in membrane potential to spread rapidly between cells , facilitating myometrial contraction As these junctions mature, uterine contraction become more frequent These are apparent initially as Braxton-Hicks, painless contraction that become obvious in 2nd half of pregnancy. Then these allow the pacemaker activity of the uterine fundus to promot th co-ordinated, fundal-dominant contraction necessary for labor

The uterus The uterus is divided into upper &lower uterine segments; the lower segment is part of the uterus & upper cervix which lie between the attachment of the peritoneum of uterovesical pouch & the level of internal os .

The uterine arteries also undergo hypertrophy in the first half of pregnancy As well as

Normally the uterus is anteverted but become more axial and vertical when enlarged and rotate in its long axis, usually to the right.

The cervix Under the influence of estradiol and progesterone, the cervix becomes swollen and softer during pregnancy. Oestradiol stimulate the growth of the columnar epithelium of the cervical canal that becomes visible on the ectocervix and is called an ectropion The cervix is often described as looking ‘bluer’ during pregnancy due to increased vascularity.

The cervical mucous becomes viscous and opaque and fills the endocervix, forming mucus plug. function?

Vagina and vulva All genetal organs undergo a marked increase in vascularity in pregnancy Estrogen cause thickening of the vaginal epithelium with increase rate of desquamation resulting in increase vaginal discharge .This discharge has a more acidic PH.

Breast After the second trimester the breast progressively increase in size, from proliferation of the glands and from deposition of fat between the lobules. Veins beneath the skin become visible and later become bluish streaks The nipple become larger, more pigmented and erectile , with colostrums secretion by the third trimester

The primary areola become larger and more deeply pigmented its base becomes raised up above the surface of breast The mouth of hypertrophied sebaceous gland appear as a number of small rounded elevations Montgomery's tubercules Later in pregnancy, secondary less pigmented areola develops, around the primary one

Skin Changes Melanocyte stimulating hormone produced by the placenta. Chloasma or the mask of pregnancy → hyperpigmentation with irregular brownish areas on the cheeks and nose. Relatively little is known about the cause of these pigmentary changes. It may be due to: Melanocyte stimulating hormone produced by the placenta. Oestrogen and progesterone may also have a melanocyte stimulating effect. linea nigra → pigmentation at the midline from the xyphoid process to the symphysis pubis

Striae gravidarum → irregular, wavy pink depression mainly on the skin of lower abdomen, and may be the buttocks and thigh due to stretching of the skin and breaking of the underlying connective tissue.

Systemic changes Volume Homeostasis The most important is fluid retention and this occurs due to There is a sodium retention Resetting of osmostat → plasma osmolality decreases. Decrease in thirst threshold → has urge to drink at lower level of plasma osmolality.

Decrease in plasma oncotic pressure → due to decrease in plasma protein by about 20% and this contribute to the increase in GFR development of peripheral oedema The consequence of fluid retention HB concentration reduced Haematocrit fall Serum albumin fall Stroke volume increase Renal blood flow increase

Cardiovascular system

Heart Rate A significant increase in heart rate occur as early as 5th week of pregnancy A progressive increase until the third trimester, when rate typically 10-15 beats / min. greater than the non pregnant one.

Cardiac Output Steady rises from an average of 4.5liters/min to about 7 liters/min flow at 20th week, and reach a plateau at 24-30 weeks gestation They are due, primarily, to an increase in stroke volume and, to a lesser extent, to a more rapid heart rate. Because Cardiac output =stroke volume× heart rate

Cardiac Size/Position/ECG The heart is enlarged by both chamber dilatation and hypertrophy. Dilation across the tricuspid valve can initiate mild regurgitant flow causing a normal grade I or II systolic murmur. The apex beat is moved outward and upward. These changes lead to common ECG findings of left axis deviation, sagging ST segments and frequently inversion or flattening of the T-wave in lead III.

Blood Pressure Early pregnancy is characterized by peripheral vasodilatation due to the vasoactive substances derived from the endothelium like nitric oxide. The diastolic blood pressure is more markedly decreased than the decrease in systolic pressure. Thus early pregnancy is associated with a relative increase in pulse pressure, but later return to the non pregnant state.

Aortocaval Compression From mid-pregnancy, the enlarged uterus compresses both the inferior vena cava (IVC)and the lower aorta when the patient lies supine; Compression of the aorta may lead to a reduction in uteroplacental and renal blood flow.

Compression of the IVC by the gravid uterus impairs venous return to the heart in supine position. Some women , develop significant supine hypotension, and loss of consciousness is possible. By rolling over on to the left side,cardiac output is almost instantly restored.

Normal changes in heart sound during pregnancy Many chnges, the most noticed: > 95% functional systolic murmur 20% transient diastolic murmur 10% continuous murmur due to increase mammary blood flow

Haematology The circulating red cell mass increases by 20–30% during pregnancy, with rises in both cell number and size. It rises more in women with multiple pregnancies, and more with iron supplementation . Serum iron concentration falls, the absorption of iron from the gut rises and iron-binding capacity rises in a normal pregnancy, since there is increased synthesis of the β1-globulin, transferrin. Plasma folate concentration halves by term, because of greater renal clearance,

Haematology Blood Volume increases progressively from 6-8 weeks gestation and reaches a maximum at approximately 32-34 weeks with little change thereafter. The blood volume returns to normal 10-14 days post partum.

The increased blood volume reduces the impact of maternal blood loss at delivery.An "autotransfusion" of blood from the contracting uterus compensates for the typical losses of 300-500 ml for vaginal births and 750-1000 ml for a Caesarean section. This can however delay the onset of the classical signs and symptoms of hypovolaemia.

Renal erythropoietin increases red cell mass by 20-30% which is a smaller rise than the plasma volume, resulting in haemodilution &a decrease in [Hb] from 13.3 g/dl to 10.5 g/dl. This is termed the physiological anaemia ofpregnancy Renal clearance of folic acid increased during pregnancy lead to fall in plasma[folate]but not the RBC [folate]

The total white cell count increases, and the average value during the third trimester is 9×109/L.

Platelet production is increased but the platelet count falls because of dilution and consumption

Coagulation there is hypercoagulable state and a reduction in plasma fibrinolytic activity. With the exception of XI and FIII, plasma concentrations of all clotting factors and fibrinogen increase.

Increase in Decrease in White cell count Red cell count Erythrocyte sedimentation rate Haemoglobin concentration Fibrinogen concentration Haematocrit Plasma folate concentration

Respiratory system Increase in pulmonary blood flow Increase in tidal volume Thoracic anatomical changes improve the airflow along the bronchial tree

Renal system &function The kidneys increase in size in pregnancy mainly because renal parenchymal volume

Urinary tract and Urinary Function Urinary tract dilatation due to smooth muscle relaxation, and by third trimester, about 97% of women have been shown to have some evidence of urinary stasis and hydronephrosis. Increase in total protein excretion (microalbuminuria), upper limit is 0.3g per day.decrease in threshould of glucose excretion

The gastrointestinal system Taste often alters very early in pregnancy. gastric emptying and intestinal transient time delayed The whole intestinal tract has decreased motility during the first two trimesters, with increased absorption of water and salt,tending to increase constipation. Heartburn is common from the increased intragastric pressure.

Gastrointestinal tract appendix displaced and reach the right flank Hemorrhoids or varicose veins may appear or worse during pregnancy.

Endocrinological Changes HCG produced within the uterus. β subunit → specific for pregnancy α subunit (differs slightly from α subunit of FSH, LH, and TSH hPL produced by the placenta (similar to prolactin and hGF)

The adrenal gland Both the plasma total and the unbound cortisol and other corticosteroid concentrations rise in pregnancy from about the end of the first trimester. Concentrations of cortisol binding globulin double.

Carbohyadrate Metabolism first half of pregnancy → fasting plasma glucose reduced Little change in insulin level second half of pregnancy → altered GTT Increase in insulin level

Thyroid function hCG may suppress thyroid-stimulating hormone (TSH) in early pregnancy because they share a common α-subunit. The thyroid remains normally responsive to stimulation by TSH and suppression by tri-iodothyronine(T3). Maternal iodine requirement increased. Total serum calcium decreased thyroid function considered to remain normal throughout the remainder of pregnancy

calcium metabolism Calcium homeostasis changes markedly Maternal total plasma calcium concentration falls, because albumin concentration falls, but unbound ionized calcium concentration is unchanged.