Physiology of Pregnancy - Hyperexcision

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Table Of Contents

Overview of Physiologic Changes in Pregnancy
Cardiovascular Changes
Respiratory Changes
Hematologic Changes
Renal Changes
Endocrine Changes
Gastrointestinal Changes
Dermatological Changes
Pelvic Examination Findings in Pregnancy

Overview of Physiologic Changes in Pregnancy

System	Changes
Cardiovascular changes	Increased heart rate by 10 – 15 bpm, increased stroke volume and cardiac output, increased intravascular volume, decreased systemic vascular resistance, decreased blood pressure in the first and second trimester
Respiratory changes	Elevated diaphragm, increased tidal volume, increased minute ventilation, decreased funcitonal residual capacity, hyperventilation with chronic compensated respiratory alkalosis
Gastrointestinal changes	Decreased competency of the lower esophageal sphincter, increased acid produciton, impaired gall bladder motility, low plasma albumin, decreased nutritional demands
Hematologic changes	Relative anaemia, leukocytosis, hypercoagulability due to increased clotting factors and decreased fibrinolysis
Renal changes	Hydronephrosis and hydroureter
Otehr changes	Decreased peritoneal irritation, increased uterine blood flow

Cardiovascular Changes

Pregnancy is a high-flow, low-resistance state. Plasma volume increases substantially (2.5 – 3.75 L), especially in multigravidas and women bearing multiple gestations.

How does cardiac output increase during pregnancy?
- It increases by 30-50%
- Increased stroke volume (30%, predominantly earlier on in pregnancy)
- Increased heart rate (15-25%; 10-20bpm, predominantly in the later stages of pregnancy which translates to an average of 80-90bpm)
Why does blood pressure decrease in pregnancy?
- Due to a substantial reduction in systemic vascular resistance (20% decrease): shunts blood to kidneys
- Diastolic pressure sees the most decrease (10-15mmHg, compared to 5-10mmHg decrease in systolic)
Why does femoral venous pressure (lower venous pressure) increase in pregnancy?
- Mechanical factors: the gravid uterus exerts pressure on the IVC, common, and external iliac veins
- There is however no change in central venous pressure
Why is there a systolic ejection murmur along the left sternal border?
- Normal due to increased flow (diastolic murmurs are pathological and warrant an echo)
Why should women be encouraged to lie on their left side during late pregnancy?
- To avoid supine hypotensive syndrome (aortocaval compression syndrome) as cardiac output is highest in the left lateral position (since the uterus no longer compresses the IVC which is located to the right of the midline)

Cardiovascular parameter	Change
Cardiac output	Increases 30-50%
Stroke volume	Increases 30%
Plasma Volume	Increases 50%
Heart rate	Increases 15-25%
Systemic vascular resistance	Decreases 20%
Systolic BP	Slight decrease of 5-10 mmHg
Diastolic BP	Decreases 20% (10-15mmHg)
Central Venous Pressure	No change
Femoral venous pressure	Increases 2-3x

Hemodynamic changes throughout pregnancy

Respiratory Changes

There is increased ventilation in pregnancy which translates into a low arterial CO2 and increased CO2 exchange at the placenta. The respiratory drive increases due to various factors (e.g. progesterone) and leads to a degree of dyspnea.

Why does residual volume decrease by 20% in pregnancy?
- The uterus causes elevation (increased excursion) of the diaphragm during exhalation
Why does PaCO2 decrease in pregnancy (chronic respiratory alkalosis)?
- Increased ventilation (Ve increases by 40%)
- Creates a higher gradient for diffusion from the fetus at the placenta
- This state of respiratory alkalosis is compensated by increased HCO3- excretion in the kidneys
What is the action of progesterone at the airway?
- Bronchodilation
What is the action of estrogen at the airway?
- Edema (Use smaller endotracheal tubes [<6mm] for intubating pregnant women)
- Hyperplasia of mucus glands
Consequence of lightening at 36-38 weeks?
- The fetal head descends the pelvis, causing less diaphragmatic compression. The woman can breathe easily
- However, she is going to have urinary frequency and urgency (the bladder is compressed)

Respiratory prameter	Change
Tidal Volume (Vt)	Increases 30-40%
Minute ventilation (Ve)	Increases 40%
Residual volume	Decreases 20%
PaCO2	Decreases 25%
Oxygen consumption	Increases 20-33%

Hematologic Changes

Hb and HCT go down because of hemodilution (dilutional anemia). Pregnancy is a hypercoagulable state (due to venous stasis and endothelial damage). Iron and folate requirements double during pregnancy. IDA is the most common cause of anemia in pregnancy (Iron study – low ferritin – is diagnostic)

Consequence of hypercoagulability in pregnancy
- 5x increases risk of DVT
- Women with inherited hypercoagulability are predisposed to placental vascular thrombosis increasing the risk of:
  - Pre-eclampsia
  - Gestational hypertension
  - Fetal complications (Miscarriage, SGA, Stillbirth)

Haematologic parameter	Change
Plasma volume	Increases 50%
RBC volume	Increases 20-30%
Hematocrit	Decreases
WBC count	Increases slightly
ESR	Increase
Coagulation factors	Increase
Coagulability	Increase
Platelet count	Unchanged

Renal Changes

Increased ureteral size, urine glucose, and mechanical factors predispose the patient to pyelonephritis and UTI. There is also some degree of proteinuria. Increased RAAS causes increased total body sodium (however serum concentration remains constant due to dilution.

Effect of lightening
- Increased urinary frequency and urgency (but makes it easier to breathe)

Renal parameter	Change
Kidney size	Increases 100%
Ureteral diameter	Increases
GFR	Increases 50%
BUN, Cr, and uric acid	Decreases 25%
Plasma Na	Unchanged
Plasma HCO2	Decreases 20%
Blood pH	Slight increase (7.4 → 7.44)
Urine glucose	Increased

Endocrine Changes

What is the predominant estrogen elevated in pregnancy?
- Estriol (produced by the placenta; fetal DHEAS → estriol)
What is the clinical relevance of pituitary hypertrophy?
- Renders it vulnerable to ischemia (Sheehan syndrome; post-partum apoplexy following PPH leading to pan-hypopituitarism)
What is the relevance of increased cortisol (increased adrenal activity) in pregnancy?
- Favors fetal lung maturity (peaks towards later pregnancy)
- Interestingly causes depression; and may render mothers susceptible to post-partum depression
Why does the thyroid increase in size?
- Higher levels of hCG which shares an a-subunit with TSH
- Mum is however euthyroid (due to increased thyroid-binding globulin)
Human placental Lactogen/Human chorionic somatomammotropin (hPL/hCs)
- Increases lipolysisAntagonizes insulin to increase blood glucose (pseudo insulin resistant state)

Estrogen	Increases
Progesterone	Increases
Pituitary size	Increases 100%
Adrenal size	Unchanged
Thyroid size	Increases 10-15%
Total thyroid hormone	Increases
Thyroid binding globulin	Increases
Free thyroid hormone	Unchanged
Human placental lactogen	Increases

Gastrointestinal Changes

Most of these are due to mechanical factors (and progesterone). Food sticks around the stomach longer. LES Sphincter tone decreases (among other factors) increasing reflux. More fluid is taken up in the colon causing harder stool (constipation). Increased hCG concentrations are associated with nausea. Hemorrhoids affect 30-40% of women. The stomach is considered “full” at all times during pregnancy ( because the fetus is compressing the stomach, even if NPO for 8-12 hours)

What contributes to reflux in pregnancy?
- Relaxed gastroesophageal sphincter
- Increased emptying time
- Decreased gastric motility
- Increased gastric pressure (mechanical)
Management of reflux in pregnancy
- Avoid trigger foods (chocolate, caffeine, alcohol)
- Treat with H2 blocker (cimetidine, ranitidine); try avoiding PPIs; can also use metoclopramide (anti-emetic that increases gastric motility)
Hyperemesis gravidarum
- Severe nausea during pregnancy that is associated with a decrease in pre-pregnancy body weight of at least 5%.
- Described as a really bad morning sickness…
- Treatment: frequent snacking and antiemetics (doxylamine/B6, antihistamines) and PPIs

Gastrointestinal Parameter	Change
Gastric motility	Decreases
Gastric emptying time	Increases
GES tone	Decreases
Colonic motility	Decreases
Colonic transit time	Increase

Dermatological Changes

Dermatological changes in pregnancy

Dermatological change	Description
Striae gravidarum	Hypopigmented streaks along the abdomen due to stretching and increased cortisol
Linea nigra and increased pigmentation of the areola	Begins at 22 – 24 weeks due to increased MSH. May witness occasional light linea nigra on the baby durin birth since MSH can cross the placenta
Chloasma (Melasma)	Blotch pigmentation of the nose and face due to increase MSH and vascularity. Also known as the “Mask of pregnancy”
Spider angiomata and palmar erythema	Due to increased vascularity

Linea nigra with striae gravidarum

Chloasma

Pelvic Examination Findings in Pregnancy

Sign	Description
Goodell’s sign	Softening of the cervix at 6 weeks LNMP. This is also seen in OCP users.
Chadwick’s sign	Bluish discolouration of the cervix
Jacquemier’s sign	Bluish (dusky) disclouration of the anterior vaginal wall due to vascular congestion at 8 weeks LNMP. This is also seen with pelvic tumors
Osiander’s sign	Increaed pulsation felt through the lateral fornices at 8 weeks LNMP. This is also seen in pelvic inflamatory disease
Palmer’s sign	Regular and rhythmic uterine contractions felt during bimanual examination between 4 – 8 weeks LNMP
Hegar’s sign	Abdominal and vaginal fingers seem to oppose below the body of the uterus during bimanual examination at 6 – 10 weeks LNMP

Reference Intervals ›

Biochemistry

ACTH	P: <80 ng/L
ALT	P: 5–35 U/L
Albumin	P: 35–50 g/L
Aldosterone	P: 100–500 pmol/L
Alk. phosphatase	P: 30–130 U/L
α-Amylase	P: 0–180 IU/dL
α-Fetoprotein	S: <10 kU/L
Angiotensin II	P: 5–35 pmol/L
ADH	P: 0.9–4.6 pmol/L
AST	P: 5–35 U/L
Bicarbonate	P: 24–30 mmol/L
Bilirubin	P: 3–17 μmol/L
BNP	P: <50 ng/L
CRP	P: <10 mg/L
Calcitonin	P: <0.1 mcg/L
Calcium (ionized)	P: 1.0–1.25 mmol/L
Calcium (total)	P: 2.12–2.60 mmol/L
Chloride	P: 95–105 mmol/L
Cholesterol	P: <5.0 mmol/L
VLDL	P: 0.128–0.645 mmol/L
LDL	P: <2.0 mmol/L
HDL	P: 0.9–1.93 mmol/L
Cortisol AM	P: 450–700 nmol/L
Cortisol Midnight	P: 80–280 nmol/L
CK ♂	P: 25–195 U/L
CK ♀	P: 25–170 U/L
Creatinine	P: 70–100 μmol/L
Ferritin	P: 12–200 mcg/L
Folate	S: 2.1 mcg/L
FSH	P: 2–8 U/L ♂; >25 menopause
GGT ♂	P: 11–51 U/L
GGT ♀	P: 7–33 U/L
Glucose (fasting)	P: 3.5–5.5 mmol/L
Growth hormone	P: <20 mu/L
HbA1C (DCCT)	B: 4–6%
HbA1C (IFCC)	B: 20–42 mmol/mol
Iron ♂	S: 14–31 μmol/L
Iron ♀	S: 11–30 μmol/L
Lactate (venous)	P: 0.6–2.4 mmol/L
Lactate (arterial)	P: 0.6–1.8 mmol/L
LDH	P: 70–250 U/L
LH	P: 3–16 U/L
Magnesium	P: 0.75–1.05 mmol/L
Osmolality	P: 278–305 mosmol/kg
PTH	P: 0.8–8.5 pmol/L
Potassium	P: 3.5–5.3 mmol/L
Prolactin ♂	P: <450 U/L
Prolactin ♀	P: <600 U/L
PSA	P: 0–4 mcg/mL
Protein (total)	P: 60–80 g/L
Red cell folate	B: 0.36–1.44 μmol/L
Renin (erect)	P: 2.8–4.5 pmol/mL/h
Renin (recumbent)	P: 1.1–2.7 pmol/mL/h
Sodium	P: 135–145 mmol/L
TBG	P: 7–17 mg/L
TSH	P: 0.5–4.2 mU/L
T4	P: 70–140 nmol/L
Free T4	P: 9–22 pmol/L
TIBC	S: 54–75 μmol/L
Triglycerides	P: 0.50–2.3 mmol/L
T3	P: 1.2–3.0 nmol/L
Troponin T	P: <0.1 mcg/L
Urate ♂	P: 210–480 μmol/L
Urate ♀	P: 150–390 μmol/L
Urea	P: 2.5–6.7 mmol/L
Vitamin B12	S: 0.13–0.68 nmol/L
Vitamin D	S: 50 nmol/L

Arterial Blood Gases

pH	7.35–7.45
PaCO₂	4.7–6.0 kPa
PaO₂	>10.6 kPa
Base excess	±2 mmol/L

Urine

Cortisol (free)	<280 nmol/24h
Hydroxyindole acetic acid	16–73 μmol/24h
Hydroxymethylmandelic acid	16–48 μmol/24h
Metanephrines	0.03–0.69 μmol/mmol cr.
Osmolality	350–1000 mosmol/kg
17-Oxogenic steroids ♂	28–30 μmol/24h
17-Oxogenic steroids ♀	21–66 μmol/24h
17-Oxosteroids ♂	17–76 μmol/24h
17-Oxosteroids ♀	14–59 μmol/24h
Phosphate (inorganic)	15–50 mmol/24h
Potassium	14–120 mmol/24h
Protein	<150 mg/24h
Protein/creatinine ratio	<3 mg/mmol
Sodium	100–250 mmol/24h

Haematology

WCC	4.0–11.0 ×10⁹/L
RBC ♂	4.5–6.5 ×10¹²/L
RBC ♀	3.9–5.6 ×10¹²/L
Hb ♂	130–180 g/L
Hb ♀	115–160 g/L
PCV ♂	0.4–0.54 L/L
PCV ♀	0.37–0.47 L/L
MCV	76–96 fL
MCH	27–32 pg
MCHC	300–360 g/L
RDW	11.6–14.6%
Neutrophils	2.0–7.5 ×10⁹/L (40–75%)
Lymphocytes	1.0–4.5 ×10⁹/L (20–45%)
Eosinophils	0.04–0.44 ×10⁹/L (1–6%)
Basophils	0–0.10 ×10⁹/L (0–1%)
Monocytes	0.2–0.8 ×10⁹/L (2–10%)
Platelets	150–400 ×10⁹/L
Reticulocytes	0.8–2.0% / 25–100 ×10⁹/L
Prothrombin time	10–14 s
APTT	35–45 s

Paediatric

Pulse Rate (bpm)
Neonate	140–160
Infant <1yr	120–140
1–5 years	110–130
5–12 years	80–120
>12 years	70–100
Respiratory Rate (tachypnoea)
0–2 months	≥60/min
2–12 months	≥50/min
1–5 years	≥40/min
>5 years	≥30/min
Blood Pressure (mmHg)
Term	65/45
1 year	75/50
4 years	85/60
8 years	95/65
10 years	100/70
Weight Formulas
3–12 months	(a + 9)/2 kg
1–6 years	2a + 8 kg
>6 years	(7a − 5)/2 kg
Haemoglobin (g/dL)
Term newborn	13–20
1 month	11–18
2 months	10–15
1–2 years	10–13
>2 years	11–14
MUAC (6 months–5 years)
Obese	>17.5 cm
Normal	13.5–17.4 cm
At risk	12.5–13.4 cm
Moderate malnutrition	11.5–12.4 cm
Severe malnutrition	<11.5 cm
Developmental Milestones
Social smile	1.5 months
Head control	4 months
Sits unsupported	7 months
Crawls	10 months
Stands unsupported	10–12 months
Walks	12–13 months
Talks	18 months
CSF WBC (/mm³)
Term newborn	0–25
>2 weeks	0–5

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