Maternal Adaptation to Pregnancy

Maternal physiology
During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications.

Cardiovascular
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 about 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.

Hematology
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.

Metabolism
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.

Nutrition
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 use of Omega 3 fatty acids supports mental and visual development of infants. Choline supplementation of research mammals supports mental development that lasts throughout life.

Gastrointestinal
nausea and vomiting ("morning sickness") may be 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

Renal
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

Pulmonary
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.

Endocrine
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

Musculoskeleton 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)

Others
Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs.