Physiology of Pregnancy Flashcards
When does pregnancy begin for clinical calculation purposes?
From the Last Menstrual Period (LMP), even though conception occurs around week 3.
When does implantation occur?
Around week 4.
How long does pregnancy last from LMP?
Approximately 280 days (40 weeks); from conception: ~266 days.
What hormone dominates in the 1st month of pregnancy?
Progesterone (P4).
How does maternal heart rate change during pregnancy?
It steadily increases, requiring cardiac remodeling.
What happens to maternal blood pressure?
Remains largely unchanged, though it can drop in mid-gestation.
Why does haematocrit fall during pregnancy?
Because plasma volume increases more than RBC mass.
How does the respiratory system adapt to pregnancy?
Increased O₂ consumption (16-20%), diaphragm elevation, thoracic breathing.
What causes increased responsiveness to PCO₂?
Progesterone increases sensitivity of chemoreceptors.
What hormone confirms implantation and supports early pregnancy?
hCG (human chorionic gonadotropin).
What does hCG stimulate?
LH receptors on the ovary → release of oestrogens and progesterone.
What structural changes occur in implantation?
Loss of zona pellucida and glycocalyx; TE cells invade decidua.
What are the three stages of villi development?
Primary: Solid trophoblast
Secondary: Mesodermal invasion
Tertiary: Blood vessels form
When is the placenta fully mature?
By around 12 weeks, but early structure appears by week 4.
What is the function of spiral artery remodeling?
Drops pressure for low-pressure nutrient-rich blood pooling.
What are the layers of the placenta based on origin?
- Amnion: Ectoderm + Mesoderm
- Chorion: Trophoblast + Mesoderm
- Yolk sac: Endoderm + Mesoderm
What is the role of the chorionic villi?
Site of nutrient/gas exchange; bathed in maternal blood.
What type of placenta do humans have?
Hemochorial – fetal villi in direct contact with maternal blood.
How much does blood volume increase during pregnancy?
By 45%.
Why might a pregnant woman appear anaemic?
Plasma volume increases more than RBCs (dilutional anaemia).
How much cardiac output goes to the placenta?
About 25%.
How does fetal Hb differ from adult Hb?
Higher oxygen affinity; 20–50% more oxygen-carrying capacity.
How is oxygen transferred to the fetus despite low PO₂?
Via fetal Hb’s higher affinity and concentration.
What’s the fetal PO₂ compared to maternal?
Maternal: ~50 mmHg; Fetal: ~30 mmHg.
Can the fetus synthesize estrogens on its own?
No, it relies on the placenta and fetal adrenals for precursors.
What does a molar pregnancy lack that a normal pregnancy has?
Oestrogens – only hCG is produced.
What are cardiovascular changes in pregnancy similar to?
Athletic remodeling – ↑ HR (20%), SV (20%), heart size (12%).
What is Chadwick’s sign?
Bluish discoloration of vagina/labia due to vascularity by ~6 wks.
Why does breathing become thoracic in pregnancy?
Due to diaphragm elevation and rib cage displacement.
What causes deeper breathing in pregnancy?
Progesterone increases chemoreceptor sensitivity.
What happens to the kidneys during pregnancy?
They enlarge; increased excretion and sodium reabsorption.
Why are UTIs more common in pregnancy?
Urinary stasis, decreased bladder tone, and glucose-rich urine.
Average maternal weight gain by the 3rd trimester?
~24 lbs (11 kg)
What hormone loosens ligaments before birth?
Relaxin.
Chance of conception at 30 vs. 40 years?
30: ~20%
40: ~5%.
Why does fertility decline with age?
Decrease in ovarian reserve and function; fewer follicles.
What are the dual roles of the placenta?
Endocrine organ and transport (gas/nutrient exchange).
What body systems undergo major changes in pregnancy?
Cardiovascular, respiratory, urinary, reproductive.
How does heart rate change in pregnancy?
Increases from ~64 bpm to ~76 bpm.
What causes blood volume to increase?
Progesterone and oestrogen promote fluid retention and vasodilation.
Why does haematocrit fall during pregnancy?
Blood volume increases more than RBC mass (dilutional effect).
How much more oxygen is consumed during pregnancy?
16–20% more.
What happens to lung volume?
Total lung capacity is slightly reduced due to elevated diaphragm.
What hormone increases sensitivity to CO₂?
Progesterone.
What does proteinuria suggest in pregnancy?
Possible preeclampsia.
What changes occur in the breasts?
Darkening of nipples/areolae, duct expansion, increased lobule size.
How does fetal heart rate change?
Rises rapidly until end of trimester 1, then steadies (~140 bpm).
How does fetal growth progress?
In distinct growth phases; rapid in third trimester.
What is colostrum?
Pre-milk substance produced before full lactation begins.
What are Braxton-Hicks contractions?
Sporadic, non-labor uterine contractions.
What is the chance of conception at age 30?
~20%.
At age 40?
~5%.
Why does fertility decline with age?
Reduced ovarian reserve and function, increased gynecological issues.
