Pregnancy

Uterus, Cervix, Ovaries, and Vagina

The uterus hypertrophies up to 15 times its length during pregnancy. Its capacity grows from 10 ml up to 5 L, while its weight grows from 50-70 g to 950-1100g. Muscle fibres cease growing by 20 weeks, and the uterus becomes progressively thinner and more cylindrical as the fetus continues to grow. There is also increased blood vessel and number, and blood flow rises from 50 ml/min up to 500 ml/min.

Braxton-Hicks contractions - spontaneous contractions that occur every few minutes from~ 24 weeks; these develop in amplitude during labor.

The cervix softens and becomes more pliable (ripens) at approximately 4 weeks (Goodell's sign) due to estrodiol's action on glycoasminoglycans in the matrix. It also becomes more cyanotic, along with the vagina, due to vascular engorgement (Chadwick's sign) at 6 weeks.

Mucous appears granular under a microscope due to progesterone. During the last weeks of pregnancy, prostaglandins and collagenases, released from leukocytes, degrade collagen and prepare for delivery.

A thick mucus plug present in the cervical os is expelled during labour (the bloody show).

Ovaries do not ovulate during pregnancy. The corpus luteum functions up to 6-8 weeks, maintained by bHCG, to produce progesterone until placenta produces its own.

The vagina shows increased vascularity (risk of bleeding), thickened mucosa, increased secretions, and muscle hypertrophy.

Breasts

Breasts undergo glandular growth with increased vascularity. Areaolar pigmentation also occurs.

Abdominal Wall and Skin

• striae gravidarium - stretch marks and also hormone-mediated
  • disappear in some women, some it does not
• rectus abdominus separation (dastasis rectii), meaning situps are impt after delivery
• pigmentation: cholasma (under eye and on bridge of nose); linea nigra (abdomen)
• spider nevi: related to massive estrogen production
• palmar erythema due to estrogen presence

Cardiovascular System

The circulation is hyperdynamic during pregnancy, with increased blood volume (150% by first trimester), cardiac output, (6.2L/min, up from 4.3 L/min), and heart rate (~83 bpm).

A widened S1 split occurs, and S2 becomes louder. Murmurs are common, along with left axis deviation.

• colloid oncotic pressure = 21 mmHg (up from 18 mm Hg)

Blood pressure dips during second trimester due to decreased peripheral vascular resistance, then increases.

Femoral venous pressure rises due to pressure of uterus, leading to edema, varicose veins, and hemorrhoids.

Supine hypotension can follow fetal compression of the aorta and vena cava. This can be treated by using a wedge on one side. Normally the woman will notice an roll over; very dangerous during exams and especially surgery.

Respiratory System

An increased oxygen requirement results in an increased tidal volume and ventilation rate. The diaphragm becomes elevated, leading to a decreased residual volume and FRC.

Blood

Hemoglobin falls at first due to hemodilution, but returns to 125 g/L at term. Leukocyte count increases, but cells are impaired. Autoimmune diseases improve.

There is a larger risk of hemorrhage during pregnancy, and the body responds with increased capacity for coagulation and decreased fibrinolysis. Increased fibrinogen, VII, VIII, IX, X, antithrombin III, plasminogen; decreased XI, XIII. The resulting hypercoagulable state increases risk of DVT, and pulmonary embolism is now a leading cause of maternal mortality in the West.

At the same time, a mild and asymptomatic gestational thrombocytopenia occurs, normalizing within 2-12 weeks of delivery.

Gastrointestinal

GERD rates increase with increased intra-abdominal pressure and decreased spincter tone and gastric emptying due to progesterone.

Progesterone also increases bile stasis, leading to gallstones, and colon stasis, leading to constipation and hemorrhoids.

The appendix is displaced upwards, leading to atypical presentation if appendicitis occurs.

Genitourinary

Urinary frequency increases as renal perfusion and the GFR increases by 50%. As a result serum creatinine falls, making it a poor measure of kindey function.

The ureters and renal pelvis dilate (hydroureter/hydronephrosis) due to progesterone-induce smooth muscle relaxation.

Rates of UTI and pyelonephritis increase.

Glycosuria can be physiologic due to increased glomerular leakiness, but prompts screening for gestational diabetes mellitus. Mild proteinuria can be present (<0.3g/24 hrs).

Endocrine

Pregnancy is a diabetogenic state, as placental production of human placental lactogen (HPL) leads to insulin resistance (similar to growth hormone). This becomes most significant mid 20 week gestation, though a lower fasting glucose is present.

Adrenal production of corticosteroids increases throughout pregnancy, playing some role in abdominal striae, glycosuria, and hypertension.

The thyroid gland enlarges due to colloid deposition. Estrogen leads to increased production of thyroxine-binding globulin, but TSH and free thyroxine index remain in the normal range.

Calcium levels drop as alumin does, though free ionized Ca remains constant due to increased PTH activity.