Chapter II - Obstetrics
Obstetrics (from the Latin obstare, "to stand by") is the surgical specialty dealing with the care of a woman and her offspring during pregnancy, childbirth and the puerperium (the period shortly after birth).
In obstetric practice, the obstetrician will see a pregnant woman on a regular basis as her pregnancy progresses. The exact schedule varies depending on resources and risk factors, such as diabetes.
The main rationale for these visits is surveillance for diseases of pregnancy, which are detectable. Some examples are:
· Pre-eclampsia. The blood pressure and urine of a pregnant woman is checked at every opportunity to check for this.
· Placenta praevia. On ultrasound, the placenta is visible obstructing the birth canal
· Abnormal presentation (late pregnancy only). The fetus may be feet-first (breech), side-on (transverse), or at an angle (oblique presentation)
· IUGR (Intrauterine Growth Restriction), this is a general designation, where the fetus is too small for its gestational age. Causes can be intrinsic (in the fetus) or extrinsic (usually placental problems). IUGR refers to fetal growth that is less than 10% of what is expected at that gestational age.
First trimester: elevated β-hCG (up to 100,000 mIU/mL by 10 weeks GA) can cause morning sickness, fatigue, mood swings and food cravings. The symptoms can last through 12 to 16 weeks of gestation.
Second trimester: The abdomen shows an obvious swelling arising from the pelvis, starting the "obvious phase" of pregnancy. Hyperpigmentation, including linea nigra may appear.
Third trimester: The mother may experience backaches due to increased strain. Typically, the curvature of the spine is changed as pregnancy evolves in order to counteract the change in weight distribution. The mother may also suffer mild urinary incontinence due to pressure on the bladder by the pregnant uterus, as well as heartburn (due to compression of the stomach).
· Bluish discoloration of vagina and cervix (Chadwick's sign)
· Softening and cyanosis of cervix after 4 weeks (Goodell's sign)
· Softening of uterus after 6 weeks (Ladin's sign)
· Breast swelling and tenderness
· Linea nigra from umbilicus to pubis
· Palmar erythema
· Nausea and vomiting
· Breast pain
· Fetal movement
During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including cardiovascular, renal, hematologic, metabolic or respiratory changes that become very important in the event of complications.
During pregnancy, both protein metabolism and carbohydrate metabolism are affected. One kilogram of extra protein is deposited, with half going to the fetus and placenta, and another half going to uterine contractile proteins, breast glandular tissue, plasma protein, and hemoglobin.
· Increased caloric requirement by 300 kcal/day
· Gain of 20 to 30 lb (10 to 15 kg)
· Increased protein requirement to 70 or 75 g/day
· Increased folate requirement from 0.4 to 0.8 mg/day (important in preventing neural tube defects)
· All patients are advised to take prenatal vitamins to compensate for the increased nutritional requirements.
The woman is the sole provider of nourishment for the embryo and later, the fetus, and so her plasma and blood volume slowly increase by 40-50% over the course of the pregnancy to accommodate the changes. This results in overall vasodilation, an increase in heart rate (15 beats/min more than usual), stroke volume, and cardiac output. Cardiac output increases by ~50%, mostly during the first trimester. The systemic vascular resistance also drops due to the smooth muscle relaxation caused by elevated progesterone, leading to a fall in blood pressure. Diastolic blood pressure consequently decreases between 12-26 weeks, and increases again to prepregnancy levels by 36 weeks. If the blood pressure remains abnormal beyond 36 weeks, the woman should be investigated for pre-eclampsia, a condition that precedes eclampsia.
· Increased tidal volume (30-40%)
· Decreased total lung capacity (TLC) by 5% due to elevation of diaphragm from uteral compression
· Decreased expiratory reserve volume
· Increased minute ventilation (30-40%) which causes a decrease in PaCO2 and a compensated respiratory alkalosis
· All of these changes can contribute to the dyspnea (shortness of breath) that a pregnant woman may experience.
· The plasma volume increases by 50% and the red blood cell volume increases only by 20-30%.
· Consequently, the hematocrit decreases.
· White blood cell count increases and may peak at over 20 mil/mL in stressful conditions.
· Decrease in platelet concentration to a minimal normal values of 100-150 mil/mL
· The pregnant woman also becomes hypercoagulable due to increased liver production of coagulation factors, mainly fibrinogen and factor VIII.
· nausea and vomiting ("morning sickness") due to elevated B-hCG, which should resolve by 14 to 16 weeks
· prolonged gastric empty time
· decreased gastroesophageal sphincter tone, which can lead to acid reflux
· decreased colonic motility, which leads to increased water absorption and constipation
· Increase in kidney and ureter size
· Increased glomerular filtration rate (GFR) by 50%, which subsides around 20 weeks postpartum
· Decreased BUN (blood urea nitrogen) and creatinine, and glucosuria (due to saturated tubular reabsorption)
· Persistent glucosuria can suggest gestational diabetes
· Increased renin-angiotensin system, causing increased aldosterone levels
· Plasma sodium does not change because this is offset by the increase in GFR
· Increased estrogen, which is mainly produced in the placenta
· Fetal well being is associated with maternal estrogen levels
· Causes an increase in thyroxine-binding globulin (TBG)
· Increased human chorionic gonadotropin (β-hCG), which is produced by the placenta. This maintains progesterone production by the corpus luteum
· Human placental lactogen (hPL) is produced by the placenta and ensures nutrient supply to the fetus. It also causes lipolysis and is an insulin antagonist, which is a diabetogenic effect.
· Increased progesterone production, first by corpus luteum and later by the placenta. Its main course of action is to relax smooth muscle.
· Increased prolactin
· Increased alkaline phosphatase
Musculoskeletal and dermatology
· Lower back pain due to a shift in gravity
· Increased estrogen can cause spider angiomata and palmar erythema
· Increase melanocyte-stimulating hormone (MSH) can cause hyperpigmentation of nipples, umbilicus, abdominal midline (linea nigra), perineum, and face (melasma or chloasma)
Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs. For the sake of comfort, many pregnant women wear larger shoes or go without. This may have something to do with the origin of the phrase "barefoot and pregnant".
The human gestation period of approximately 40 weeks between the time of the last menstrual cycle and delivery is traditionally divided into three periods of three months, or trimesters.
The first trimester is the period of time from the first day of the last menstrual period through 12 weeks of gestation. It is during this period that the embryo undergoes most of its early structural development. Most miscarriages occur during this period.
The second trimester is the period of time extending from the 13th to the 27th week of gestation. During this period the embryo, now known as a fetus, is recognizable as human in form, but is not developed enough to be viable if born.
The third trimester is the period of time extending from the 28th week of gestation to delivery. It is during this period that the fetus reaches viability, and may survive if born prematurely.
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Chapter II - Obstetrics