Physiology of Pregnancy

Question 1

When does pregnancy begin for clinical calculation purposes?

Answer 1

From the Last Menstrual Period (LMP), even though conception occurs around week 3.

Question 2

When does implantation occur?

Answer 2

Around week 4.

Question 3

How long does pregnancy last from LMP?

Answer 3

Approximately 280 days (40 weeks); from conception: ~266 days.

Question 4

What hormone dominates in the 1st month of pregnancy?

Answer 4

Progesterone (P4).

Question 5

How does maternal heart rate change during pregnancy?

Answer 5

It steadily increases, requiring cardiac remodeling.

Question 6

What happens to maternal blood pressure?

Answer 6

Remains largely unchanged, though it can drop in mid-gestation.

Question 7

Why does haematocrit fall during pregnancy?

Answer 7

Because plasma volume increases more than RBC mass.

Question 8

How does the respiratory system adapt to pregnancy?

Answer 8

Increased O₂ consumption (16-20%), diaphragm elevation, thoracic breathing.

Question 9

What causes increased responsiveness to PCO₂?

Answer 9

Progesterone increases sensitivity of chemoreceptors.

Question 10

What hormone confirms implantation and supports early pregnancy?

Answer 10

hCG (human chorionic gonadotropin).

Question 11

What does hCG stimulate?

Answer 11

LH receptors on the ovary → release of oestrogens and progesterone.

Question 12

What structural changes occur in implantation?

Answer 12

Loss of zona pellucida and glycocalyx; TE cells invade decidua.

Question 13

What are the three stages of villi development?

Answer 13

Primary: Solid trophoblast
Secondary: Mesodermal invasion
Tertiary: Blood vessels form

Question 14

When is the placenta fully mature?

Answer 14

By around 12 weeks, but early structure appears by week 4.

Question 15

What is the function of spiral artery remodeling?

Answer 15

Drops pressure for low-pressure nutrient-rich blood pooling.

Question 16

What are the layers of the placenta based on origin?

Answer 16

• Amnion: Ectoderm + Mesoderm
• Chorion: Trophoblast + Mesoderm
• Yolk sac: Endoderm + Mesoderm

Question 17

What is the role of the chorionic villi?

Answer 17

Site of nutrient/gas exchange; bathed in maternal blood.

Question 18

What type of placenta do humans have?

Answer 18

Hemochorial – fetal villi in direct contact with maternal blood.

Question 19

How much does blood volume increase during pregnancy?

Answer 19

By 45%.

Question 20

Why might a pregnant woman appear anaemic?

Answer 20

Plasma volume increases more than RBCs (dilutional anaemia).

Question 21

How much cardiac output goes to the placenta?

Answer 21

About 25%.

Question 22

How does fetal Hb differ from adult Hb?

Answer 22

Higher oxygen affinity; 20–50% more oxygen-carrying capacity.

Question 23

How is oxygen transferred to the fetus despite low PO₂?

Answer 23

Via fetal Hb’s higher affinity and concentration.

Question 24

What’s the fetal PO₂ compared to maternal?

Answer 24

Maternal: ~50 mmHg; Fetal: ~30 mmHg.

Question 25

Can the fetus synthesize estrogens on its own?

Answer 25

No, it relies on the placenta and fetal adrenals for precursors.

Question 26

What does a molar pregnancy lack that a normal pregnancy has?

Answer 26

Oestrogens – only hCG is produced.

Question 27

What are cardiovascular changes in pregnancy similar to?

Answer 27

Athletic remodeling – ↑ HR (20%), SV (20%), heart size (12%).

Question 28

What is Chadwick’s sign?

Answer 28

Bluish discoloration of vagina/labia due to vascularity by ~6 wks.

Question 29

Why does breathing become thoracic in pregnancy?

Answer 29

Due to diaphragm elevation and rib cage displacement.

Question 30

What causes deeper breathing in pregnancy?

Answer 30

Progesterone increases chemoreceptor sensitivity.

Question 31

What happens to the kidneys during pregnancy?

Answer 31

They enlarge; increased excretion and sodium reabsorption.

Question 32

Why are UTIs more common in pregnancy?

Answer 32

Urinary stasis, decreased bladder tone, and glucose-rich urine.

Question 33

Average maternal weight gain by the 3rd trimester?

Answer 33

~24 lbs (11 kg)

Question 34

What hormone loosens ligaments before birth?

Answer 34

Relaxin.

Question 35

Chance of conception at 30 vs. 40 years?

Answer 35

30: ~20% 40: ~5%.

Question 36

Why does fertility decline with age?

Answer 36

Decrease in ovarian reserve and function; fewer follicles.

Question 37

What are the dual roles of the placenta?

Answer 37

Endocrine organ and transport (gas/nutrient exchange).

Question 38

What body systems undergo major changes in pregnancy?

Answer 38

Cardiovascular, respiratory, urinary, reproductive.

Question 39

How does heart rate change in pregnancy?

Answer 39

Increases from ~64 bpm to ~76 bpm.

Question 40

What causes blood volume to increase?

Answer 40

Progesterone and oestrogen promote fluid retention and vasodilation.

Question 41

Why does haematocrit fall during pregnancy?

Answer 41

Blood volume increases more than RBC mass (dilutional effect).

Question 42

How much more oxygen is consumed during pregnancy?

Answer 42

16–20% more.

Question 43

What happens to lung volume?

Answer 43

Total lung capacity is slightly reduced due to elevated diaphragm.

Question 44

What hormone increases sensitivity to CO₂?

Answer 44

Progesterone.

Question 45

What does proteinuria suggest in pregnancy?

Answer 45

Possible preeclampsia.

Question 46

What changes occur in the breasts?

Answer 46

Darkening of nipples/areolae, duct expansion, increased lobule size.

Question 47

How does fetal heart rate change?

Answer 47

Rises rapidly until end of trimester 1, then steadies (~140 bpm).

Question 48

How does fetal growth progress?

Answer 48

In distinct growth phases; rapid in third trimester.

Question 49

What is colostrum?

Answer 49

Pre-milk substance produced before full lactation begins.

Question 50

What are Braxton-Hicks contractions?

Answer 50

Sporadic, non-labor uterine contractions.

Question 51

What is the chance of conception at age 30?

Answer 51

~20%.

Question 52

At age 40?

Answer 52

~5%.

Question 53

Why does fertility decline with age?

Answer 53

Reduced ovarian reserve and function, increased gynecological issues.