Physiological changes during pregnancy

Physiological changes during pregnancy

1. PHYSIOLOGICAL CHANGES DURING PREGNANCY Prepared by, Pinki Sah Lecturer BHC

2. During pregnancy there is progressive anatomical, physiological and biochemical change not only confined to the genital organs but also to all systems of the body. This is principally a phenomenon of maternal adaptation to the increasing demands of the growing fetus. Unless well understood, these physiological adaptations of normal pregnancy can be misinterpreted as pathological.

3. GENITAL ORGANS

4. VULVA: Vulva becomes edematous and more vascular; superficial varicosities may appear especially in multipara. Labia minora are pigmented and hypertrophied . VAGINA: Vaginal walls become hypertrophied, edematous and more vascular. Increased blood supply of the venous plexus surrounding the walls gives the bluish coloration of the mucosa ( Jacquemier ’ s sign ) . The length of the anterior vaginal wall is increased .

5. Secretion: The secretion becomes copious, thin and curdy white due to marked exfoliated cells and bacteria.

6. UTERUS

7. There is enormous growth of the uterus during pregnancy. The uterus which in non-pregnant state weighs about 60 g, with a cavity of 5–10 mL and measures about 7.5 cm in length, at term, weighs 900–1,000 g and measures 35 cm in length. The capacity is increased by 500–1,000 times. Changes occur in all the parts of the uterus—body, isthmus and cervix .

8. BODY OF THE UTERUS There is increase in growth and enlargement of the body of the uterus . Enlargement: The enlargement of the uterus is affected by the following factors : Changes in the muscles — Hypertrophy and hyperplasia : Not only the individual muscle fiber increases in length and breadth but also there is limited addition of new muscle fibers. These occur under the influence of the hormones—estrogen and progesterone—limited to the first half of pregnancy but pronounced up to 12 weeks.

9. Stretching: The muscle fibers further elongate beyond 20 weeks due to distension by the growing fetus. The wall becomes thinner and, at term, measures about 1.5 cm or less. The uterus feels soft and elastic in contrast to firm feel of the nongravid uterus.

10. There is simultaneous increase in number and size of the supporting fibrous and elastic tissues . Vascular system— Whereas in the non-pregnant state, the blood supply to the uterus is mainly through the uterine and least through the ovarian but, in the pregnant state , the latter carries as much the blood as the former. There is marked spiraling of the arteries, reaching the maximum at 20 weeks; thereafter, they straighten out.

11. The uterine enlargement is not a symmetrical one. The fundus enlarges more than the body . Weight: The increase in weight is due to the increased growth of the uterine muscles, connective tissues and vascular channels . Shape —Non-pregnant pyriform shape is maintained in early months. It becomes globular at 12 weeks. As the uterus enlarges, the shape once more becomes pyriform or ovoid by 28 weeks and changes to spherical beyond 36th week

12. Position Normal anteverted position is exaggerated up to 8 weeks. Thus, the enlarged uterus may lie on the bladder rendering it incapable of filling, clinically evident by frequency of micturition. Afterwards, it becomes erect, the long axis of the uterus conforms more or less to the axis of the inlet.

13. As the term approaches, especially in multipara with lax abdominal wall, there is a tendency of anteversion . But in primigravida with good tone of the abdominal muscles, it is held firmly against the maternal spine.

14. Contractions (Braxton-Hicks ) Uterine contraction in pregnancy has been named after Braxton-Hicks who first described its entity during pregnancy. From the very early weeks of pregnancy, the uterus undergoes spontaneous contraction. This can be felt during bimanual palpation in early weeks or during abdominal palpation when the uterus feels firmer at one moment and softer at another.

15. Although spontaneous, the contractions may be excited by rubbing the uterus. The contractions are irregular, infrequent, spasmodic and painless without any effect on dilatation of the cervix. The patient is not conscious about the contractions.

16. Endometrium: The changes of the endometrium of the non-pregnant uterus into decidua of pregnancy

17. ISTHMUS During the first trimester, isthmus hypertrophies and elongates to about 3 times its original length. It becomes softer. With advancing pregnancy beyond 12 weeks, it progressively unfolds from above, downward until it is incorporated into the uterine cavity. The circularly arranged muscle fibers in the region.

18. function as a sphincter in early pregnancy and thus help to retain the fetus within the uterus. Incompetency of the sphincteric action leads to mid-trimester abortion and the encirclage operation done to rectify the defect is based on the principle of restoration of the retentive function of the isthmus

19. CERVIX Stroma : There are hypertrophy and hyperplasia of the elastic and connective tissues. Fluids accumulate inside and in between the fibers. Vascularity is increased especially beneath the squamous epithelium of the portio vaginalis which is responsible for its bluish coloration.

20. There are marked hypertrophy and hyperplasia of the glands which occupy about half the bulk of the cervix. All these lead to marked softening of the cervix ( Goodell’s sign) It not only provides diagnostic aid in pregnancy but also the changes in the cervix facilitate its dilatation during labor .

21. Epithelium: There is marked proliferation of the endocervical mucosa with downward extension beyond the squamocolumnar junction .

22. Secretion: The secretion is copious and tenacious-physiological leucorrhea of pregnancy. This is due to the effect of progesterone. There is no alteration in the relation of the cervix. There is unfolding of the isthmus; beginning 12 weeks onwards and takes part in the formation of the lower uterine segment. Variable amount of effacement is noticed near term in primigravidae . In multiparae , the canal is slightly dilated.

23. FALLOPIAN TUBE As the uterine end rises up and the fimbrial end is held up by the infundibulopelvic ligament, it is placed almost vertical by the side of the uterus . The total length is somewhat increased . The tube becomes congested. Muscles undergo hypertrophy. Epithelium becomes flattened, and patches of decidual reaction are observed.

24. OVARY The growth and function of the corpus luteum reaches its maximum at 8th week when it measures about 2.5 cm and becomes cystic. It looks bright orange, later on becomes yellow and, finally pale. Regression occurs following decline in the secretion of human chorionic gonadotropin ( hCG ) from the placenta. Hormones—estrogen and progesterone—secreted by the corpus luteum maintain the environment for the growing ovum before the action is taken over by the placenta.

25. These hormones not only control the formation and maintenance of decidua of pregnancy but also inhibit ripening of the follicles. Thus both the ovarian and uterine cycles of the normal menstruation remain suspended. Luteoma of pregnancy results from exaggerated luteinization reaction of the ovary.

26. BREAST The changes in the breasts are best evident in a primigravida. In multipara, who has once lactated, the changes are not clearly defined . SIZE: Increased size of the breasts becomes evident even in early weeks. This is due to marked hypertrophy and proliferation of the ducts (estrogen) and the alveoli (estrogen and progesterone) which are marked in the peripheral lobules. There is also hypertrophy of the connective tissue stroma . Quite often, the “axillary tail” becomes enlarged and painful.

27. NIPPLES AND AREOLA: The nipples become larger, erectile and deeply pigmented. Variable number of sebaceous glands (5–15) which remain invisible in the non-pregnant state in the areola, become hypertrophied and are called Montgomery’s tubercles . Those are placed surrounding the nipples. Their secretion keeps the nipple and the areola moist and healthy. An outer zone of less marked and irregular pigmented area appears in second trimester and is called secondary areola .

28. SECRETION: Secretion (colostrum) can be squeezed out of the breast at about 12th week which at first becomes sticky. Later on, by 16th week, it becomes thick and yellowish. The demonstration of secretion from the breast of a woman who has never lactated is an important sign of pregnancy. In latter months, colostrum may be expressed from the nipples.

29. CUTANEOUS CHANGES 1. Face ( chloasma gravidarum or pregnancy mask): It is an extreme form of pigmentation around the cheek , forehead and around the eyes. It may be patchy or diffuse; disappears spontaneously after delivery . 2. Breast : 3. Abdomen : Linea nigra : It is a brownish black pigmented area in the midline stretching from the xiphisternum to the symphysis pubis. The pigmentation disappears after delivery.

30. Striae gravidarum : These are slightly depressed linear marks with varying length and breadth found in pregnancy. They are predominantly found in the abdominal wall below the umbilicus, sometimes over the thighs and breasts. These stretch marks represent the scar tissues in the deeper layer of the cutis .

31. Apart from the mechanical stretching of the skin, increase in aldosterone production during pregnancy are the responsible factors. Controlled weight gain during pregnancy and massaging the abdominal wall by lubricants like olive oil may be helpful in reducing their formation.

32. OTHER CUTANEOUS CHANGES: These include vascular spider and palmar erythema which are due to high estrogen level. Mild degrees of hirsutism may be observed and in puerperium the excess hair is lost.

33. WEIGHT GAIN The total weight gain during the course of a singleton pregnancy for a healthy woman averages 11 kg (24 lb ). This has been distributed to 1 kg in first trimester and 5 kg each in second and third trimester. The total weight gain at term is distributed approximately as follows :

34. Ideally weight gain should depend on pre-pregnancy body mass index (BMI) level. Weight gain for a woman with normal BMI (20–26) is 11–16 kg. An obese woman (BMI > 30) should not gain more than 7 kg, whereas an underweight woman (BMI < 19) may be allowed to gain up to 18 kg . Maternal nutrition and weight gain during pregnancy are directly related to the newborn weight. However , it may not be a specific indicator as there are other factors for low birth weight infant.

35. BODY WATER METABOLISM During pregnancy, the amount of water retained at term is about 6.5 liters. The water content of the fetus , placenta and amniotic fluid is about 3.5 liters . Pregnancy is a state of hypervolemia. There is active retention of sodium (900 mEq ), potassium (300 mEq ) and water . The important causes of sodium retention and volume overload are: changes in maternal osmoregulation,

36. (ii) increased estrogen and progesterone, (iii) increase in renin-angiotensin-aldosterone system (RAAS) activity, (iv) increased aldosterone, deoxycorticosterone , (v) control by arginine vasopressin (AVP) from posterior pituitary and (vi) atrial natriuretic peptide.

37. Increase in water intake due to lowered osmotic threshold for thirst causes polyuria in early pregnancy.

38. HEMATOLOGICAL CHANGES BLOOD VOLUME: During pregnancy, there is increased vascularity of the enlarging uterus with the interposition of uteroplacental circulation. The activities of all the systems are increased. Blood volume is markedly raised during pregnancy .

39. The rise is progressive and inconsistent. All the constituents of blood are affected with increased blood volume. The blood volume starts to increase from about 6 th week, expands rapidly thereafter to maximum 40–50% above the nonpregnant level at 30–34 weeks . The level remains almost static till delivery

40. PLASMA VOLUME: It starts to increase by 6 weeks and it plateaus at 30 weeks of gestation. The rate of increase almost parallels to that of blood volume but the maximum is reached to the extent of 50 % . Total plasma volume increases to the extent of 1.25 liters . The increase is greater in multigravida, in multiple pregnancy and with large baby.

41. RBC AND HEMOGLOBIN: The RBC mass is increased to the extent of 20–30% . The total increase in volume is about 350 mL. This increase is regulated by the increased demand of oxygen transport during pregnancy . RBC mass begins to increase at about 10 weeks and continues till term without plateauing. Iron supplementation increases the RBC mass by 30%. Reticulocyte count increases by 2%. Erythropoietin level is raised.

42. The disproportionate increase in plasma and RBC volume produces a state of hemodilution (fall in hematocrit) during pregnancy. Thus , even though the total hemoglobin mass increases during pregnancy to the extent of 18–20%, there is apparent fall in hemoglobin concentration. At term, the fall is about 2 g% from the non-pregnant value. There is simultaneous fall in number of red cells by 15–20% and the hematocrit level. The excess of circulating hemoglobin left behind after delivery yields iron for storage.

43. LEUKOCYTES and IMMUNE SYSTEM: Neutrophilic leukocytosis occurs to the extent of 8,000/mm3 and even to 20,000/mm3 in labor. The increase may be due to rise in the levels of estrogen and cortisol. The major change in the immune system is the modulation away from cell-mediated cytotoxic immune response toward increased humoral innate immune responses

44. TOTAL PROTEIN :

45. BLOOD COAGULATION FACTORS : Pregnancy is a hypercoagulable state .

46. CARDIOVASCULAR SYSTEM ANATOMICAL CHANGES Due to elevation of the diaphragm consequent to the enlarged uterus, the heart is pushed upward and outward with slight rotation to left CARDIAC OUTPUT: The cardiac output (CO) starts to increase from 5th week of pregnancy and reaches its peak 40–50% at about 30–34 weeks. Thereafter the CO remains static till term.

47. CO is lowest in the sitting or supine position and highest in the right or left lateral or knee chest position. Cardiac output increases further during labor (+50%) and immediately following delivery (+70%) over the pre-labor values. MAP also rises. There is squeezing out of blood from the uterus into the maternal circulation (auto transfusion) during labor and in the immediate postpartum. CO returns to pre-labor values by 1 hour following delivery and to the pre-pregnant level by another 4 weeks time .

48. BLOOD PRESSURE: Systemic vascular resistance (SVR ) decreases (–21%) due to smooth muscle relaxing effect of progesterone, NO prostaglandins . In spite of the large increase in cardiac output , the maternal BP (BP = CO × SVR) is decreased due to decrease in SVR. There is overall decrease in diastolic blood pressure (BP) and mean arterial pressure (MAP) by 5–10 mm Hg .

49. SUPINE HYPOTENSION SYNDROME (POSTURAL HYPOTENSION): During late pregnancy, the gravid uterus produces a compression effect on the inferior vena cava when the patient is in supine position. This , however, results in opening up of the collateral circulation by means of paravertebral and azygos veins. In some cases (10%), when the collateral circulation fails to open up, the venous return of the heart may be seriously curtailed.

50. This results in production of hypotension, tachycardia and syncope. The normal blood pressure is quickly restored by turning the patient to lateral position . The augmentation of the venous return during uterine contraction prevents the manifestation from developing during labor.

51. METABOLIC CHANGES GENERAL METABOLIC CHANGES: Total metabolism is increased due to the needs of the growing fetus and the uterus. Basal metabolic rate is increased to the extent of 30% higher than that of the average for the nonpregnant women.

52. SYSTEMIC CHANGES RESPIRATORY SYSTEM: With the enlargement of the uterus, especially in the later months, there is elevation of the diaphragm by 4 cm. Total lung capacity is reduced by 5% due to this elevation. However, diaphragmatic excursion is increased by 1–2 cm and breathing becomes diaphragmatic.

53. Total pulmonary resistance is reduced due to progesterone effect. The mucosa of the nasopharynx becomes hyperemic and edematous. This may cause nasal stuffiness and rarely epistaxis. The woman feels shortness of breath.

54. URINARY SYSTEM : Kidney — There is dilatation of the ureters , renal pelvis and the calyces. The kidneys enlarge in length by 1 cm. Renal plasma flow is increased by 50–75%, maximum by the 16 weeks and is maintained until 34 weeks. Thereafter it falls by 25%. Glomerular filtration rate (GFR) is increased by 50 % all throughout pregnancy .

55. Ureter: Ureters become atonic due to high progesterone level. Dilatation of the ureter above the pelvic brim with stasis is marked on the right side especially in primigravidae . There is marked hypertrophy of the muscle and the sheath of the ureter especially the pelvic part probably due to estrogen. There is elongation , kinking and outward displacement of the ureters . The dilatation effect resolves by 6 weeks postpartum.

56. Bladder: There is marked congestion with hypertrophy of the muscles and elastic tissues of the wall. Increased frequency of micturition is noticed at 6–8 weeks of pregnancy which subsides after 12 weeks. It may be due to resetting of osmoregulation causing increased water intake and polyuria . .

57. In late pregnancy , frequency of micturition once more reappears due to pressure on the bladder as the presenting part descends down the pelvis. Stress incontinence may be observed in late pregnancy due to urethral sphincter weakness

58. ALIMENTARY SYSTEM: The gums become congested and spongy and may bleed to touch. Muscle tone and motility of the entire gastrointestinal tract are diminished due to high progesterone level. Cardiac sphincter is relaxed and regurgitation of acid gastric content into the esophagus may produce chemical esophagitis and heart burn.

59. Dyspepsia is common. There is diminished gastric secretion and delayed emptying time of the stomach. Risk of peptic ulcer disease is reduced. Atonicity of the gut leads to constipation, while diminished peristalsis facilitates more absorption of food materials.

60. LIVER AND GALLBLADDER: Although there is no histological change in the liver cells, but the functions are depressed. With the exception of raised alkaline phosphatase levels, other liver function tests (serum levels of bilirubin, AST, ALT, CPK, LDH) are unchanged.

61. There is mild cholestasis (estrogen effect). There is marked atonicity of the gallbladder (progesterone effect). This, together with high blood cholesterol level during pregnancy, favors stone formation .

62. NERVOUS SYSTEM: Some sorts of temperamental changes are found during pregnancy and in the puerperium . Nausea , vomiting, mental irritability and sleep disorders are probably due to some psychological background. Postpartum blues, depression or psychosis may develop in a susceptible Individual.

63. Compression of the median nerve underneath the flexor retinaculum over the wrist joint leading to pain and paresthesia in the hands and arm (Carpal tunnel syndrome) may appear in the later months of pregnancy. Similarly, paresthesia and sensory loss over the anterolateral aspect of the thigh may occur. It is due to compression of the lateral cutaneous nerve of the thigh.