SECTION 4: MATERNAL CHANGES DURING PREGNANCY
1. Changes in reproductive system
1.1 Uterus: There are obvious changes in the uterus during pregnancy.
1.1.1 Corpus
There is increase in growth of the body of the uterus. The uterus which in non-pregnant state weight about 50 gm and measures about 7.5cm in length, at term, weighs 900-1000gm and measures 35cm in length at full term. The increase of uterus is due to the increased growth of uterine muscles.
The fastest growth happens at the findus of uterus as the most muscle fibers are concentrated there. The lower uterine segment undergoes a growth slower than the fundus, in the cervix demonstrates the slowest growth. By the end of 12 weeks, the enlarged uterine will be outside the pelvic cavity.
As the uterus enlarges to occupy the abdominal cavity, it usually rotates on its long axis to the right （dexto-rotation）. This is due to the occupation of the rectosigmoid in the left posterior quadrant of the pelvis.
Uterine irregular contraction at 12 to 14 weeks' pregnancy have been named after Brsxton-Hicks who first described its entity during pregnancy. This can be felt during bimanual palpation in early weeks or during bimanual palpation when the uterus feels firmer at one moment and softer at an-other. The contractions are irregular, infrequent spasmodic and painless without any effect on dilatation of the cervix. They can be appreciated by the mother at times.
1.1.2 Uterine Isthmus
There are important structural and functional changes in the isthmus during pregnancy. During the first trimester of pregnancy, isthmus hypertrophies and elongates to about 3 times its original length. It becomes softer, especially in 10 weeks. With advancing pregnancy beyond 12 weeks, it progressively unfolds from above, downwards until it is incorporated into the uterine cavity. During parturient, it could changes to be a part of birth canal which would extent to 7-10 centimeters.
2. The changes of circulatory system
2.1 Heart: Due to elevation of the diaphragm consequent to the enlarged uterus, the heart is pushed upwards and out-wards with slight rotation to the left. The apex beat is shifted to the 4th intercostal space about 1-2cm outside the midclavicular line. A systolic murmur may be audible in the apical or pulmonary area. This is due to decreased blood viscosity and torsion of the great vessels.
ECG reveals normal pattern except evidences of left axis deviation.
2.2 Cardiac output: Cardiac output starts to increase from 10th week of pregnancy, reaches its peak at about 32-34 weeks.
Thereafter the cardiac output remains about 80ml（+30%）static till term when the observation is made at lateral recumbent position.
2.3 Blood pressure: Inspite of the large increase in cardiac output, the maternal blood pressure is decreased due to decrease in systemic vascular resistance during the first and second trimester of pregnancy. There is overall decrease in diastolic blood pressure（BP）and mean arterial pressure（MAP）, but no obvious changes in systolic pressure.
2.4 Venous pressure: Antecubital venous pressure remains unaffected. Femoral venous pressure is markedly raised, especially in the later months. It is due to pressure exerted by the gravid uterus on the common iliac veins, more on the right side due to dextro-rotation of the uterus. The venous pressure is quickly restored by turning the patient to lateral position. Distensibility of the veins and stagnation of blood in the venous system explain the development of oedema, varicose veins, piles （haemorrhoids）and deep vein thrombosis.
Supine hypotension syndrome（postural hypotension）:During the late pregnancy, the gravid uterus produces a compression effect on the inferior vena cava when the patient is in supine position, thus reducing Cardiac output. This results in production of hypotension, tachycardia and syncope.
3. Changes of blood
3.1 Maternal blood volume: The blood volume starts to increase from about 6-8 weeks, expands rapidly thereafter to maximum 40-45% above the nonpregnant level at 32 to 34 weeks. The level remains almost static till term. Total plasma volume increases to the extent of 1450ml. The total increase of RBC in volume is about 450ml.
3.2 Blood components
3.2.1 Erythrocytes: Moderate erythroid hyperplasia is present in the bone marrow, and the reticulocyte count is elevated slightly during normal pregnancy. Whole blood viscosity decreases. Hemoglobin concentration at term averages 125 g/L, and in approximately 5 percent of women, it is below 110 g/L.
Importantly, the iron stores of normal pregnant women are only approximately 500 mg. Due to Iron Requirements for in-creased RBC, normal pregnancy, the fetus and placenta, and other genital organs, iron deficiency usually coexist during the pregnancy. Pregnant woman should be given supplemental iron after midpregnancy to prevent the decrease of haemoglobin values.
3.2.2 Leucocytes: Neutrophilic leucocytosis increases from 7-8weeks, and will reach the peak at 30 weeks which occurs to the extent of 5—12×10⋆9/L and even to 15×10⋆9/L.
Clinical considerations: Careful clinical correlation is needed to diagnose infections along with increase in leucocytes.
3.2.3 Blood coagulation factors: during the pregnancy, blood is in a hypercoagulable state. There is a upregulation of clotting factors like II, V, VII, VIII, IX, X, but no obvious changes in blood platelet number. PT and APTT show a slight shortening in the third trimester of pregnancy. Overall, blood clotting time does not show any significant change.
3.2.4 Plasma protein: Due to the hemodilution , the plasma protein concentration falls to 60—65g/L.The reduction mainly occurs in albumin, it is about 35g/L in plasma.
4. Changes of urinary system
The kidneys enlarge in length by 1cm during pregnancy.Renal plasma flow is increased by 35%. Glomerular filtration rate（GFR）is increased by 50% all through pregnancy. Out-put of urine in the night is more than in the day.
The appreciable increase in glomerular filtration, together with impaired tubular reabsorptive capacity for filtered glucose, accounts in most cases for glucosuria about 15% pregnant women spill glucose in the urine after meal.
Ureters becomes atonic due to high progesterone. Dilatation of the ureter above the pelvic with stasis is marked on the right side especially in primigravidae. It is due to greater compression due to the right dextrorotation of uterus.
Clinical considerations: pregnant woman are vulnerable to acute pyelonephritis, especially on the right kidney.
5. Functional changes in lungs:
5.1 The lung capacity increases obviously.
5.2 About 40% increase in minute ventilation, and 39% in tidal volume.
5.3 20% decrease in residual volume.
5.4 Alveolar ventilation increases about 65%.
5.5 The upper respiratory tract mucous membrane will be thick, and mild hyperemic edema.
Clinical considerations: Easily exposed to upper respiratory tract infection.
6. Changes in the digestive system
6.1 Bleeding gums due to the effect of a large amount of estrogen during pregnancy
6.2 Burning sensation in the stomach
6.3 Abdominal distension
6.4 Hemorrhoids
6.5 Cholestasis
7. Changes of endocrine system
7.1 Pituitary Gland
7.1.1 Gonadotropic hormone:FHS and LH are down regulated
7.1.2 Maternal plasma level of prolactin increases markedly during normal pregnancy compared with nonpregnant women.
7.2 Adrenocortical hormone
7.2.1 Cortisol is increased obviously, but only 10% of the cortisol is free cortisol which have biological activity in body.
7.2.2 Aldosterone is upregulated
7.2.3 Testosterone increases, pubes and armpit hair will grow more.
7.3 Thyroid Gland
Anatomically, the thyroid gland undergoes moderate enlargement during pregnancy caused by glandular hyperplasia and increased vascularity, subclinical hyperthyroidism
8. Cutaneous changes
8.1 The distribution of pigmentation are around nipples, areola, linea alba, vulva.
8.2 Chloasma may appear during the pregnancy and may be patchy or diffuse.
8.3 Striae gravidarum, it is pinkish in priimipara, be comes glistening white in multipara.
9. General metabolic changes
9.1 Basal metabolic rate slightly decreased in early pregnancy and then gradually increased in mid-pregnancy. Basal metabolic rate is 15-20% higher than that of the average for the non-pregnant women.
9.2 The weight remains static before 12th weeks. From the 13th weeks onwards the weight gain is about 0.5 kg per week till term. The total weight gain during the course of a singleton pregnancy for a healthy woman averages 12.5kg.
9.3 Pregnant women's fasting blood glucose is slightly lower than the nonpregnant women.
9.4 Urine ketone usually appears when hyperemesis gravidarum occurs.
9.5 Enough protein and minerals are needed to supply the development of fetus. Calcium and Iron should be supplemented.
10. Changes of skeletons, joints and ligaments
In pregnant women: due to the gravid uterus the center of gravity is displaced forward, Head and shoulders are thrown backward to compensate for this. This produces the typical lordotic gait of pregnant women. Osteoporosis, pain in lumbosacral portion, ischialgia, symphyseolysis usually occus as complications in pregnant women.
（冯祥 潘苗苗）