Department of Obstetrics and Gynecology, Peking University First Hospital
1. Basic concepts
The first is fertilization. Fertilization is the process by which sperm penetrates the egg to form a fertilized egg. Pregnancy is the process of embryo and fetus growth and development in the uterine cavity. Egg fertilization is the beginning of pregnancy, and the fetus and placenta are delivered from the mother, which is the end of pregnancy. The gestation period refers to the time before the sperm and egg combine to form a fertilized egg, the pregnant egg is implanted in the uterine cavity, and the placenta and fetus grow and mature before being discharged from the body. The entire pregnancy period is about 280 days, also known as 40 gestational weeks, which can be divided into 3 periods: early pregnancy, middle pregnancy and late pregnancy.
Early pregnancy refers to menopause to 12 weeks + 6 days of pregnancy, middle pregnancy refers to 13 weeks of pregnancy to 27 weeks + 6 days of pregnancy, and the third trimester is after 28 weeks of pregnancy.
2. Local changes during pregnancy
(1) Changes in the vulva and vagina
Changes in the reproductive system include changes in the vulva and vagina. First, the extensibility of the vulva is enhanced, local hyperemia, thickened skin, pigmentation of the labia majora, increased blood vessels in the labia majora, and soft connective tissue. Second, the vaginal stretchability is enhanced, the vaginal mucosa is colored and thickened, the folds increase, and the connective tissue becomes soft. Third, the defense function of the vagina is enhanced. There are more exfoliated cells in the vagina, and the secretion is mushy. The pH of the vagina also changes. Due to the influence of a large amount of estrogen and progesterone, the glycogen in the vaginal epithelial cells accumulates and is decomposed into lactic acid by Lactobacillus, which increases the pH in the vagina and helps prevent bacterial infections.
(2) Changes in the uterus
The first is menopause. The uterus gradually enlarges and softens. At 12 weeks of pregnancy, the uterus enlarges beyond the pelvic cavity. In the third trimester, due to the sigmoid colon on the left side of the pelvis, the uterus has different degrees of dextrorotation. The second is the increase in uterine cavity volume, from 10ml in non-pregnancy to 1500ml in term pregnancy. The cheeks of the uterus are also elongated and thinned, gradually elongated at 12 weeks of gestation, from 1cm in non-pregnancy to 7-10cm in term. There are more blood vessels in the cervix, the edema changes in purple-blue color, and the glandular secretions of the cervical canal increase to form mucus plugs to prevent the invasion of bacteria.
(3) Changes in the ovaries
The ovary stops ovulating, and its volume increases slightly. Before 10 weeks of pregnancy, the corpus luteum produces estrogen and progesterone to maintain pregnancy. After 10 weeks, the function of the corpus luteum is replaced by the placenta.
(4) Changes in breasts
During early pregnancy, the breasts are obviously enlarged and congested, the nipples are colored and darkened, and the sebaceous glands on the areola form sprout nodules. The large amount of estrogen secreted by the placenta stimulates the development of mammary ducts, progesterone stimulates the development of mammary glands, pituitary hormone, Placentapoietin and others are involved in the development and perfection of mammary glands and prepare for breastfeeding. During the third trimester, the breasts will have light yellow and thin colostrum outflow. At this time should pay attention to breast care, avoid excessive stimulation of the nipple, so as not to cause contractions.
3. Systemic changes during pregnancy
(1) Changes in the circulatory system
1. Heart changes during pregnancy
The position of the heart has changed. Due to the elevation of the diaphragm, the heart shifts to the left, up, and forward. The increase in heart volume increases by about 10% from the first trimester to the end of pregnancy. At the same time, the blood flow and the speed of blood flow also increase. The heart rate in the third trimester can generally increase by 10-15 times per minute.
Increase in cardiac output and blood volume. First, the increase in cardiac output peaks from the 10th week of pregnancy to the 32nd and 34th weeks of pregnancy, and the peak continues until delivery. After labor, especially in the second stage of labor, the cardiac output has a significant increase. The increase in blood volume begins at 6 weeks of gestation and reaches its peak at 32 to 34 weeks of gestation. The increase in blood volume is 1500ml, which is about 35% increase. Among them, plasma increases by 1000ml, and red blood cells increase by 500ml, making it easy to develop physiological anemia during pregnancy.
2. Changes in venous pressure
Pregnancy increases the blood volume of pelvic blood flowing back to the inferior vena cava, and the right circumflexion of the uterus compresses the inferior vena cava to obstruct the blood return, which is prone to lower limbs and perineal varicose and hemorrhoids. When lying on the supine position for a long time, it can also cause a decrease in the amount of blood returned to the heart, a decrease in cardiac output, and a drop in blood pressure, which is called supine syndrome or supine hypotension syndrome.
3. Changes in blood composition
The first is the change of red blood cells. During pregnancy, the bone marrow continuously produces red blood cells. The red blood cells increase slightly, but the increase in blood volume is less. Due to blood dilution, iron-deficiency anemia is prone to occur during pregnancy. In order to meet the growth and development of the fetus and the physiological changes of the mother's various organs and to adapt to the increase in red blood cells, in the middle and late pregnancy, attention should be paid to increasing the intake of iron-rich foods. The second is the change of coagulation factors. The coagulation factors are increased, the platelets have no obvious changes, and the blood is in a hypercoagulable state, which helps prevent postpartum hemorrhage. The change of plasma protein during pregnancy is mainly due to the decrease of albumin. Due to blood dilution, it begins to decrease from the first trimester. In the second trimester, the plasma protein is about 60-65g/L and remains until delivery.
(2) Changes in the urinary system
Renal plasma flow and glomerular filtration rate have both increased. During pregnancy, the increase in metabolites increases the burden on the mother’s kidneys. Renal blood flow increases by 35% compared with non-pregnancy. The glomerular filtration rate is higher than Increased by 50% during non-pregnancy. Due to the influence of renal plasma flow and glomerular filtration rate, urine output increases in the supine position, so nocturia during pregnancy increases.
During early pregnancy, due to the enlarged uterus compressing the bladder, pregnant women often experience frequent urination. As the gestational age increases, the uterus enlarges beyond the pelvic cavity. Generally, the above symptoms disappear at 12 weeks of pregnancy. In the third trimester, due to the fetal presentation dropping into the pelvis, pregnant women may again experience frequent urination and urine overflow, mainly caused by the fetal presentation re-pressing the bladder. Because the glomerular filtration rate increases and the renal tubule reabsorption of glucose cannot increase correspondingly, about 15% of pregnant women have urine sugar, which should be differentiated from gestational diabetes. Under the influence of progesterone during pregnancy, the smooth muscle tension of the urinary system is reduced, and the renal pelvis and ureter are slightly dilated in the second trimester, and urine reflux can occur. Pregnant women are prone to acute pyelonephritis.
(3) Changes in the respiratory system
During the first trimester, the rib cage widens and increases, the diaphragm rises, and the diaphragm activity during breathing also increases. The increase in lung ventilation in the second trimester is greater than the oxygen consumption, which is beneficial to provide oxygen for pregnant women and fetuses. Pregnant women in the third trimester of pregnancy are mainly chest breathing, and the gas exchange remains unabated. As the diaphragm rises, pregnant women breathe deeply and have difficulty breathing after lying down. They should choose a lateral position or raise their head to relieve symptoms.
(4) Changes in the digestive system
Pregnant women in early pregnancy will experience various degrees of nausea, vomiting, loss of appetite and other early pregnancy reactions, which usually disappear at 12 weeks of pregnancy. In the second and third trimesters, due to the influence of estrogen, the smooth muscle tension of the digestive tract is reduced, the bowel movement is reduced and weakened, and the time for gastric emptying is prolonged. Pregnant women often experience fullness in the upper abdomen. Due to the rise of the diaphragm, the stomach is compressed and the pylorus When the dilator muscles relax, the contents of the stomach will also flow back to the lower part of the esophagus, causing a burning sensation in the stomach; bowel movements are weakened and constipation occurs.
(5) Other changes during pregnancy
1. Weight change
Weight gain during pregnancy includes fetus, placenta, amniotic fluid, uterus, breast, blood, tissue fluid, and fat accumulation. The ideal average gain 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 causes increased melanin, skin pigmentation, and pregnancy spots.
The entire gestation period is 280 days, that is, 40 gestational weeks. Various maternal systems have undergone a series of physiological changes and functional adjustments, in order to meet the needs of fetal growth and delivery, and to prepare for postpartum breastfeeding. In order to adapt to these physiological changes, nutrition management during pregnancy should be done to ensure the health of mothers and babies.