I. Basic concepts First of all, fertilization. Fertilization is the process by which a sperm penetrates an egg to form a fertilized egg. Pregnancy is the process of growth and development of the embryo and fetus in the uterine cavity. Fertilization of the egg is the beginning of pregnancy, and delivery of the fetus and placenta from the mother is the end of pregnancy. The gestation period is the time before the sperm and egg unite to form a fertilized egg, the pregnant egg settles in the uterine cavity, and the placenta and fetus grow and develop to maturity and are expelled from the body. The entire gestation period is about 280 days, also known as 40 weeks of pregnancy, and can be divided into 3 periods: early pregnancy, middle pregnancy and late pregnancy. Early pregnancy is from menopause to 12 weeks + 6 days of pregnancy, middle pregnancy is from 13 weeks of pregnancy to 27 weeks + 6 days of pregnancy, and late pregnancy is after 28 weeks of pregnancy. Local changes during pregnancy (a) Changes in vulva and vagina Changes in reproductive system include changes in vulva and vagina. Firstly, the vulva becomes more extended, locally congested, the skin thickens, the labia majora and minora become pigmented, the blood vessels in the labia majora increase, and the connective tissues become soft and loose. Secondly, the vaginal extension increases, the vaginal mucosa becomes thicker with coloring, more folds and softer connective tissue. Thirdly, the defensive function of the vagina is enhanced. The shedding cells of the vagina increase and the secretions become paste-like. The pH level of the vagina also changes. Due to the influence of large amounts of estrogen and progesterone, glycogen in the vaginal epithelium accumulates and is broken down into lactic acid by Lactobacillus, which enhances the pH of the vagina and helps prevent bacterial infection. (ii) Changes in the uterus Firstly, menopause, the uterus gradually increases in size and softness, and at 12 weeks of pregnancy, the uterus increases beyond the pelvic cavity. In late pregnancy, due to the sigmoid colon on the left side of the pelvis, the uterus is mostly right-sided to varying degrees. Secondly, the volume of the uterine cavity increases, from 10 ml in non-pregnancy to 1500 ml in full-term pregnancy. the cheek of the uterus is also elongated and thinned, gradually elongating from 1 cm in non-pregnancy to 7-10 cm in full-term pregnancy at 12 weeks of gestation. the cervix becomes more vascular and edematous with a purple-blue change, and the glandular secretions of the cervical canal increase to form a mucus tether to prevent the invasion of bacteria. (iii) Changes in the ovaries The ovaries stop ovulating and increase slightly in size. The pregnancy is maintained by the corpus luteum producing estrogen and progesterone until 10 weeks of gestation, and after 10 weeks the corpus luteum function is replaced by the placenta. (iv) Changes in breasts During early pregnancy, breasts are obviously enlarged and engorged, nipples are colored and darkened, sebaceous glands on the areola form budding nodules, a large amount of estrogen secreted by the placenta stimulates the development of milk ducts, progesterone stimulates the development of breast glandular follicles, pituitary hormone and placental hormone are involved in the development and perfection of the breast, ready for breastfeeding. During late pregnancy, there will be thin yellowish colostrum coming out of the breasts. At this time, attention should be paid to breast care and avoid over-stimulation of the nipples to avoid contractions. (a) Changes in the circulatory system (1) Changes in the heart during pregnancy The position of the heart has changed, as the diaphragm rises, causing the heart to shift to the left, up and forward. The heart volume increases from early pregnancy to the end of pregnancy by about 10%, while the blood flow and the speed of blood flow also increase, and the heart rate can generally increase by 10-15 times per minute in late pregnancy. The increase of cardiac output and blood volume. Firstly, the increase in cardiac output starts from the 10th week of pregnancy and reaches a peak between the 32nd and 34th weeks of pregnancy, and the peak is maintained until delivery, and after delivery, especially in the second stage of labor, there is another significant increase in cardiac output. The increase of blood volume starts from 6 weeks of pregnancy and reaches the peak between 32 and 34 weeks of pregnancy, the increase of blood volume is 1500ml, about 35%, among which the increase of plasma is 1000ml and the increase of red blood cells is 500ml, which makes it very easy to have physiological anemia during pregnancy. 2. Changes in venous pressure Pregnancy increases the amount of pelvic blood flowing back to the inferior vena cava, and the rightward rotation of the uterus compresses the inferior vena cava so that blood flow is blocked, making it easy for varicose veins and hemorrhoids to occur in the lower limbs and perineum. When prolonged supine position, it can also cause the reduction of cardiac blood return, lower cardiac output, so that blood pressure drops, known as supine syndrome, also known as supine hypotension syndrome. 3, changes in blood components First of all, the change of red blood cells, bone marrow during pregnancy constantly produce red blood cells, red blood cells mildly increased, but less than the increase in blood volume. Due to blood dilution, iron deficiency anemia is likely to occur during pregnancy. In order to meet the needs of fetal growth and development and physiological changes in various organs of the mother and to adapt to the increase in red blood cells, attention should be paid to increasing the intake of iron-rich foods in the middle and late stages of pregnancy. The second is the change of coagulation factors. All coagulation factors increase, platelets do not change significantly, and blood is in a hypercoagulable state, which helps prevent postpartum bleeding. The changes of plasma protein, mainly the decrease of clear protein during pregnancy, due to hemodilution, began to decrease since early pregnancy, and by mid-pregnancy, the plasma protein was about 60-65g/L, which was maintained until delivery. (ii) Changes in the urinary system Renal plasma flow and glomerular filtration rate are increased. During pregnancy, due to the increase in metabolites, which increases the burden on the mother’s kidneys, renal blood flow is 35% higher than during non-pregnancy, and glomerular filtration rate is 50% higher than during non-pregnancy. Nocturia increases during pregnancy because renal plasma flow and glomerular filtration rate are influenced by body position, and urine output increases in the supine position. In early pregnancy, pregnant women often experience frequent urination due to the pressure of the enlarged uterus on the bladder. As the weeks of pregnancy increase, the uterus increases beyond the pelvis, and the above symptoms usually disappear at 12 weeks of pregnancy. In late pregnancy, as the fetal dew descends into the pelvis, pregnant women can again experience frequent urination and urine overflow, mainly due to the pressure of the fetal dew on the bladder again. Due to the increase of glomerular filtration rate and the inability of renal tubular reabsorption of glucose to increase correspondingly, urinary sugar occurs in about 15% of pregnant women and should be distinguished from diabetes mellitus in pregnancy. The smooth muscle tone of the urinary system is reduced during pregnancy under the influence of progesterone, and the renal pelvis and ureter are mildly dilated in mid-pregnancy, and the phenomenon of urine reflux can occur, and pregnant women are prone to acute pyelonephritis. (C) Changes in the respiratory system The thorax widens and increases during early pregnancy, the diaphragm rises, and the amplitude of diaphragmatic activity increases during breathing. The increase in ventilation of the lungs in mid-pregnancy is greater than the oxygen consumption, which is conducive to the provision of oxygen for the pregnant woman and the fetus. Pregnant women in late pregnancy are predominantly thoracic breathers, and gas exchange remains undiminished. As the diaphragm rises, pregnant women breathe deeper and have difficulty breathing after lying down, they should choose to lie on their side or padding their head to relieve the symptoms. (IV) Changes of digestive system Early pregnancy reactions such as nausea, vomiting and loss of appetite will occur in varying degrees during early pregnancy, which usually disappear in the 12th week of pregnancy. In the middle and late pregnancy, due to the influence of estrogen, the smooth muscle tone of the digestive tract decreases, intestinal peristalsis decreases and weakens, the time of gastric emptying is prolonged, and pregnant women often experience a feeling of fullness in the upper abdomen; as the diaphragm rises, the stomach is pressurized, the dilator muscle of the pylorus loosens, and the stomach contents also reflux to the lower part of the esophagus, causing a burning sensation in the stomach; intestinal peristalsis weakens and constipation occurs. (E) other changes during pregnancy 1, changes in weight Weight gain during pregnancy includes the fetus, placenta, amniotic fluid, uterus, breasts, blood, tissue fluid, and fat accumulation, the most ideal average growth during pregnancy is 12.5 kg. 2.Increased demand for minerals The growth and development of the fetus requires a large amount of calcium, phosphorus, iron and other minerals. Therefore, attention should be paid to mineral supplementation during pregnancy. 3, skin changes The effect of increased progesterone increases melanin, skin pigmentation, and stretch marks. The whole gestation period is 280 days, i.e. 40 gestational weeks. A series of physiological changes and functional regulation of the mother’s systems occur to meet the needs of fetal growth and development and delivery, as well as to prepare for postpartum breastfeeding. In order to adapt to these physiological changes, the nutritional management of pregnancy should be done well to ensure the health of mother and child.