Obstetrics
Seán Keenan
2022
,Physiological Changes in Pregnancy
Hormonal
Physiological Changes
- Progesterone
o Corpus Luteum: Produces to 35 d post-conception
o Placenta: Produces progesterone past 35 d mark
o Effects: ↓ Smooth m. excitability; ↑ Body To
- Oestrogens (90 % Oestradiol)
o Effects: ↑ Breast growth; Water retention
o Thyroid: Often enlarges due to ↑ colloid
- Other Hormones
o Prolactin: Production in pituitary increased
o Cortisol: ↑ Output but ↔ unbound levels
o βHCG: ↑ Until 8 wks then plateaus and falls
Cardiovascular System
Physiological Changes
- Stroke Volume: SV ↑ 30 % - BP: SBP ↔; DBP ↓ in 1TM + 2TM; ↔ in 3TM
- Heart Rate: HR ↑ 15 % - Venous: Uterus may interfere with LL return
- Cardiac Output: CO ↑ 15 % - NB: Ankle oedema; Varicose veins; Supine ↓ BP
Respiratory System
Physiological Changes
- Ventilation: ↑ 40 %; Tidal volume ↑ 500-700 mL - Oxygen: Requirements ↑ 20 %
- NB: Caused by progesterone’s effect on resp. centre - BMR: Basal metabolic rate ↑ 15 % (thyroid/ACTH)
Circulatory System
Physiological Changes
- Blood: Blood volume ↑ 30 % (mostly in 2TM) - Fibrinolysis: ↓ Fibrinolytic activity (risks VTE)
- NB: Red cells ↑ 20 % but plasma ↑ 50 % (↓ Hb) - NB: Prevent excess bleeding in delivery
- COAGs: Slight ↑ in coagulants - Other: ↑ WCC; ↑ ESR; ↓ PTC
- NB: Fibrinogen; Factors VII, VIII, X
Urinary System
Physiological Changes
- Blood Flow: ↑ 30 % - Reabsorption: Salt + H2O ↑ by ↑ sex steroids
- GFR: ↑ 30-60 %; Leads to glycosuria + Proteinuria - Proteinuria: ↑ Urinary protein losses
Biochemical
Physiological Changes
- Calcium: ↑ Requirements during gestation (esp. 3TM) - Serum: ↓ Ca2+ (ionised Ca2+ stable); ↓ PO43-
- Placenta: Actively transported across placenta - Gut: Absorption increases to compensate
Liver
Physiological Changes
- Blood flow: Remains the same - Albumin: ↓ Levels
- ALP: ↑ 50 %
Uterus
Physiological Changes
- Mass: 100 g ➔ 1100 g (Hyperplasia ➔ hypertrophy) - Contractions: Braxton-Hicks occur at ~30 wks
- Cervix: ↑ Cervical ectropion and discharge - NB: Irregular; Occur every 20 mins; Progressive
- Position: Retroversion may cx urinary retention cervical changes are absent
, Plasma Chemistry in Pregnancy
Non-Pregnant Trimester 1 Trimester 2 Trimester 3
Centile / Analyte 2.5 97.5 2.5 97.5 2.5 97.5 2.5 97.5
+
Na mmol/L 138 146 135 141 132 140 133 141
2+
Ca mmol/L 2 2.6 2.3 2.5 2.2 2.2 2.2 2.5
Albumin Corrected Ca2+ 2.3 2.6 2.25 2.57 2.3 2.5 2.3 2.59
Albumin g/L 44 50 39 49 36 44 33 41
AST IU/L 7 40 10 28 11 29 11 30
AST IU/L 0 40 6 32 6 32 6 32
TSH 0 4 0 1.6 1 1.8 7 7.3
Analyte Non-Pregnant Pregnancy
ALP IU/L 3 300 ≤450*
Bicarcbonate mmol/L 24 30 20 25
Creatinine µmol/L 70 150 24 68
Urea mmol/L 2.5 6.7 2 4.2
Urate µmol/L 150 390 116 276
* ALP can be drastically raised in normal pregnancy
Normal Growth
Phases of Growth
- Phase I: 0-16 wks; Cellular hyperplasia - Phase III: 32 wks – Term; Hypertrophy
- Phase II: 16-32 wks; Hyperplasia + Hypertrophy
Production of Blood Products in Foetus
Hepatic Haematopoiesis Splenic Haematopoiesis
- Major: Major site of initial haematopoiesis - Minor: Minor site of haematopoiesis
- Begins: 6 wks gestation - Active: 12-25 wks gestation
- Peaks: 12-16 wks gestation Bone Marrow
- Declines: 36 wks gestation - Active: From 16 wks gestation ➔ Adulthood
, Prenatal Care
Description
The aim is to minimize the risks to the mother, neonate, or fetus by modifying pre-pregnancy conditions and risk
factors. This may involve advising against pregnancy or delaying conception until a safer time. Babies conceived 18–
23 months after a live birth have the lowest rate of perinatal problems. See paediatrics for Neural tube defects notes.
Basics of Prenatal Care
Weight Smoking
- Exercise: Encourage; Improves fitness + self-esteem - Mother: ↓ Fallopian tube fxn + ovulation
- Weight: Aim >18.5 and <30 - Father: Abnormal sperm production
- Avoid: Contact sports (abdominal trauma) - Miscarriage: Associated with 2-fold ↑ risk
Nutritional - Other: Preterm labour; ↓ Foetal growth; Placenta
- Folate: See below praevia; Abruption; Asthma RR 1.5
- Avoid: Liver; Vit A; Caffeine; Pâté; Soft cheese; Sushi Alcohol
- VitD: At risk ethnic groups; Obesity; Chronic disease - Mother: High levels risk foetal alcohol syndrome
- NB: VitD deficiency leads to ↑ risk of Pre-eclampsia; - Miscarriage: ↑ Risk of miscarriage
IUGR; T1DM; Asthma; Fractures; Rickets
Serology
- Rubella: Ensure immune to rubella
Folic Acid in Pregnancy
Functions Risk Factors for NTD
- THF: Necessary for FNA and RNA synthesis - FHx: NTD in either parent; Previous NTD pregnancy
Causes of Deficiency - Meds: Antiepileptic medication
- Drugs: Phenytoin; Methotrexate; Alcohol - Maternal: Coeliac disease; DM; Thalassaemia trait
- Physiological: Alcohol excess - Obesity: BMI >30 kg/m2
Consequences of Deficiency Prevention of Deficiency
- Haem: Macrocytic megaloblastic anaemia - ↔ Risk: 400 µg folate until 12 wks gestation
- Neuro: Neural tube defects (NTDs) - ↑ Risk: 5 mg folate 1 month preconception-12 wks
MORE Folate (B9) – Indications for 5 mg Antenatal Care Booking
- Metabolic Disorder (DM; Coeliac) - Blood (4): FBC; Rh; Group; Alloantibodies
- Obesity (BMI >30) - Virus (3): HBV; HIV; Syphilis
- Relative (FHx or Hx of NTDs) - Urine (2): Urine dipstick; Urine culture
- Epilepsy (on AEDs) - Exam (1): Full physical observations
- B(9)lood (SCA; Thalassemia)
Seán Keenan
2022
,Physiological Changes in Pregnancy
Hormonal
Physiological Changes
- Progesterone
o Corpus Luteum: Produces to 35 d post-conception
o Placenta: Produces progesterone past 35 d mark
o Effects: ↓ Smooth m. excitability; ↑ Body To
- Oestrogens (90 % Oestradiol)
o Effects: ↑ Breast growth; Water retention
o Thyroid: Often enlarges due to ↑ colloid
- Other Hormones
o Prolactin: Production in pituitary increased
o Cortisol: ↑ Output but ↔ unbound levels
o βHCG: ↑ Until 8 wks then plateaus and falls
Cardiovascular System
Physiological Changes
- Stroke Volume: SV ↑ 30 % - BP: SBP ↔; DBP ↓ in 1TM + 2TM; ↔ in 3TM
- Heart Rate: HR ↑ 15 % - Venous: Uterus may interfere with LL return
- Cardiac Output: CO ↑ 15 % - NB: Ankle oedema; Varicose veins; Supine ↓ BP
Respiratory System
Physiological Changes
- Ventilation: ↑ 40 %; Tidal volume ↑ 500-700 mL - Oxygen: Requirements ↑ 20 %
- NB: Caused by progesterone’s effect on resp. centre - BMR: Basal metabolic rate ↑ 15 % (thyroid/ACTH)
Circulatory System
Physiological Changes
- Blood: Blood volume ↑ 30 % (mostly in 2TM) - Fibrinolysis: ↓ Fibrinolytic activity (risks VTE)
- NB: Red cells ↑ 20 % but plasma ↑ 50 % (↓ Hb) - NB: Prevent excess bleeding in delivery
- COAGs: Slight ↑ in coagulants - Other: ↑ WCC; ↑ ESR; ↓ PTC
- NB: Fibrinogen; Factors VII, VIII, X
Urinary System
Physiological Changes
- Blood Flow: ↑ 30 % - Reabsorption: Salt + H2O ↑ by ↑ sex steroids
- GFR: ↑ 30-60 %; Leads to glycosuria + Proteinuria - Proteinuria: ↑ Urinary protein losses
Biochemical
Physiological Changes
- Calcium: ↑ Requirements during gestation (esp. 3TM) - Serum: ↓ Ca2+ (ionised Ca2+ stable); ↓ PO43-
- Placenta: Actively transported across placenta - Gut: Absorption increases to compensate
Liver
Physiological Changes
- Blood flow: Remains the same - Albumin: ↓ Levels
- ALP: ↑ 50 %
Uterus
Physiological Changes
- Mass: 100 g ➔ 1100 g (Hyperplasia ➔ hypertrophy) - Contractions: Braxton-Hicks occur at ~30 wks
- Cervix: ↑ Cervical ectropion and discharge - NB: Irregular; Occur every 20 mins; Progressive
- Position: Retroversion may cx urinary retention cervical changes are absent
, Plasma Chemistry in Pregnancy
Non-Pregnant Trimester 1 Trimester 2 Trimester 3
Centile / Analyte 2.5 97.5 2.5 97.5 2.5 97.5 2.5 97.5
+
Na mmol/L 138 146 135 141 132 140 133 141
2+
Ca mmol/L 2 2.6 2.3 2.5 2.2 2.2 2.2 2.5
Albumin Corrected Ca2+ 2.3 2.6 2.25 2.57 2.3 2.5 2.3 2.59
Albumin g/L 44 50 39 49 36 44 33 41
AST IU/L 7 40 10 28 11 29 11 30
AST IU/L 0 40 6 32 6 32 6 32
TSH 0 4 0 1.6 1 1.8 7 7.3
Analyte Non-Pregnant Pregnancy
ALP IU/L 3 300 ≤450*
Bicarcbonate mmol/L 24 30 20 25
Creatinine µmol/L 70 150 24 68
Urea mmol/L 2.5 6.7 2 4.2
Urate µmol/L 150 390 116 276
* ALP can be drastically raised in normal pregnancy
Normal Growth
Phases of Growth
- Phase I: 0-16 wks; Cellular hyperplasia - Phase III: 32 wks – Term; Hypertrophy
- Phase II: 16-32 wks; Hyperplasia + Hypertrophy
Production of Blood Products in Foetus
Hepatic Haematopoiesis Splenic Haematopoiesis
- Major: Major site of initial haematopoiesis - Minor: Minor site of haematopoiesis
- Begins: 6 wks gestation - Active: 12-25 wks gestation
- Peaks: 12-16 wks gestation Bone Marrow
- Declines: 36 wks gestation - Active: From 16 wks gestation ➔ Adulthood
, Prenatal Care
Description
The aim is to minimize the risks to the mother, neonate, or fetus by modifying pre-pregnancy conditions and risk
factors. This may involve advising against pregnancy or delaying conception until a safer time. Babies conceived 18–
23 months after a live birth have the lowest rate of perinatal problems. See paediatrics for Neural tube defects notes.
Basics of Prenatal Care
Weight Smoking
- Exercise: Encourage; Improves fitness + self-esteem - Mother: ↓ Fallopian tube fxn + ovulation
- Weight: Aim >18.5 and <30 - Father: Abnormal sperm production
- Avoid: Contact sports (abdominal trauma) - Miscarriage: Associated with 2-fold ↑ risk
Nutritional - Other: Preterm labour; ↓ Foetal growth; Placenta
- Folate: See below praevia; Abruption; Asthma RR 1.5
- Avoid: Liver; Vit A; Caffeine; Pâté; Soft cheese; Sushi Alcohol
- VitD: At risk ethnic groups; Obesity; Chronic disease - Mother: High levels risk foetal alcohol syndrome
- NB: VitD deficiency leads to ↑ risk of Pre-eclampsia; - Miscarriage: ↑ Risk of miscarriage
IUGR; T1DM; Asthma; Fractures; Rickets
Serology
- Rubella: Ensure immune to rubella
Folic Acid in Pregnancy
Functions Risk Factors for NTD
- THF: Necessary for FNA and RNA synthesis - FHx: NTD in either parent; Previous NTD pregnancy
Causes of Deficiency - Meds: Antiepileptic medication
- Drugs: Phenytoin; Methotrexate; Alcohol - Maternal: Coeliac disease; DM; Thalassaemia trait
- Physiological: Alcohol excess - Obesity: BMI >30 kg/m2
Consequences of Deficiency Prevention of Deficiency
- Haem: Macrocytic megaloblastic anaemia - ↔ Risk: 400 µg folate until 12 wks gestation
- Neuro: Neural tube defects (NTDs) - ↑ Risk: 5 mg folate 1 month preconception-12 wks
MORE Folate (B9) – Indications for 5 mg Antenatal Care Booking
- Metabolic Disorder (DM; Coeliac) - Blood (4): FBC; Rh; Group; Alloantibodies
- Obesity (BMI >30) - Virus (3): HBV; HIV; Syphilis
- Relative (FHx or Hx of NTDs) - Urine (2): Urine dipstick; Urine culture
- Epilepsy (on AEDs) - Exam (1): Full physical observations
- B(9)lood (SCA; Thalassemia)
