Physiologic changes in pregnancy

• Classic presentation of pregnancy

  Woman with a regular menstrual cycle who presents with amenorrhea, nausea, vomiting, generalized malaise, and breast tenderness
• Early changes in pregnancy

  • Enlarged uterus after bimanual examination
  • Breast changes i.e tenderness
  • Softening and enlargement of the cervix (Hegar sign; observed at approximately 6 wk)
  • Chadwick sign - bluish discoloration of the cervix from venous congestion (observed by 8-10 weeks)
  • Gravid uterus may be palpable low in the abdomen (usually by 12 weeks)
• HCG


  Appears in the urine as early as 10 days after gestation with 99% accuracy
• Other hormones used for pregnancy tests

  • Progesterone
  • Early pregnancy factor
• Ultrasonography


  Can be used for dating and as a screening examination for fetal anomalies, but it is not typically used for diagnosis
• Probable signs of pregnancy

  • Chadwick's sign
  • Goodell's sign
  • Hegar's sign
  • Evidence on ultrasound of gestational sac
  • Ballotment
  • Braxton's hick contraction
  • Fetal outline felt by the examiner
• Placental hormones


  • Human chorionic gonadotropins (HCG)
  • Human chorionic somatomammotropins (HCS)
  • Human chorionic thyrotropin
  • Placental progesterone
  • Placental oestrogens
  • Relaxin
• Human chorionic gonadotropins (HCG)


  A polypeptide (largest active peptide), detected in maternal blood as early as 6-8 days after conception, peaks between 60 and 90 days of gestation, then decreases to a very low level and just before labour its level falls to zero
• HCG secretion pattern


  1. Peaks at 10 weeks, 5 μg/mL (end of first trimester)

  2. Then decreases to a lower plateau
• Human chorionic somatomammotropin (HCS)


  Protein in nature and resembles growth hormone structurally, secretion begins at fifth week of pregnancy, increases gradually throughout pregnancy and its plasma concentration is directly proportional to the weight of placenta, peaks at term with a value of 15 mg/mL, functions as maternal growth hormone of pregnancy and causes deposition of protein in the tissues and brings about nitrogen, calcium and potassium retention
• Placental progesterone secretion


  1. During early pregnancy, it is synthesized by corpus luteum and then by syncytiotrophoblasts of placenta (85% of total contribution)

  2. During pregnancy, plasma concentration rises steadily throughout gestation, reaches a maximum plateau at 30-40 weeks of gestation

  3. Just before the onset of labour, its level decreases
• Placental progesterone


  • Promotes the growth of endometrium
  • Has a marked inhibitory effect on the contractions of uterus
  • Causes development of alveolar system of mother's breast in synergy with oestrogen
  • Has an immunosuppressive role in protecting the fetus
  • Acts as a precursor for the corticosteroid synthesis by the fetal adrenal cortex
• Placental estrogen secretion


  1. Quantitatively oestriol is the major oestrogen of pregnancy with smaller amount of oestradiol and oestrone

  2. Increases to term
• Placental estrogen


  • Causes growth and development of maternal reproductive organs
  • Stimulates development of lactiferous ductal system in mammary glands
  • Stimulates renin secretion
  • Just before term, oestrogen to progesterone ratio increases and uterus is dominated by oestrogen
• Relaxin


  A polypeptide hormone that inhibits uterine contractions, facilitates delivery by relaxing the pubic symphysis and softening and dilating the cervix, and plays a role in development of mammary glands
• Other hormones that increase during pregnancy

  • Oxytocin
  • ADH
  • Adrenocorticosteroids
  • Glucocorticoids
  • Androgens
• Thyroid hormones T3 and T4


  Levels increase hence predisposition to hyperthyroidism
• Changes in insulin response during pregnancy

  • Inhibition of insulin facilitation of glucose entry into cells at the cell membrane receptors by both the steroids and the placental peptides
  • Inhibition of glycogenesis with increased glycogenolysis
  • Similar effects on lipid metabolism with increase in circulating FFA's
  • Use of oral hypoglycaemic agents not appropriate
  • Insulin requirement drops sharply after parturition
• Pregnancy is diabetogenic
• Changes in genital organs during pregnancy

  • Uterus: Increase in size due to hypertrophy and hyperplasia of myometrium smooth muscle fibers, weight increases from 30-50 g to 1000-1200 g at full term, length increases from 7.5 cm to 35cm at term, thickness of the wall decreases from 1.25 cm to 5 mm at term, volume increases from few ml to about 5-7 L at term, shape changes from pyriform to globular
  • Ovaries: Corpus luteum enlarges during first 12-16 weeks then degenerates, placenta takes over secretion of oestrogens and progesterone
  • Cervix: Softens, endocervix gets hypertrophied, cervical glands increase in number forming a plug that closes the cervical canal
  • Fallopian tubes: Pushed upwards due to increase in uterus size, hyperplasia of epithelial cells and increased blood supply
  • Mammary glands: Hyperplasia of ductal and alveolar tissue, areola becomes pigmented, sebaceous glands become prominent, nipples become larger and pigmented
• Weight gain during pregnancy

  A woman may gain total of 10-12 kg, contributed by: Fetus: 3 kg, Placenta and amniotic fluid: 1.5 kg, Uterus and breast enlargement: 1.0 kg, Increase in blood volume and interstitial fluid: 1.5 kg, Fat deposition: 3.5 to 4 kg
• Weight loss in early pregnancy

  May be observed due to excessive vomiting
• Absence of weight gain in 2nd or 3rd trimester


  Is a sign of fetal growth retardation and fetal death
• Oedema occurs especially in the lower limbs during pregnancy
• Components of gestational weight gain

  • Fetus: 3 kg
  • Placenta and amniotic fluid: 1.5 kg
  • Uterus and breast enlargement: 1.0 kg
  • Increase in blood volume and interstitial fluid: 1.5 kg
  • Fat deposition: 3.5 to 4 kg
• A woman may gain total of 10-12 kg of weight during normal pregnancy
• Weight loss may be observed in early pregnancy


  Because of excessive vomiting
• Absence of weight gain in the second or third trimester

  Is a sign of foetal growth retardation and foetal death
• Oedema occurs especially in the lower limbs

  Because of pressure of gravid uterus on the femoral vein and also because of Na+ and water retention (increased levels of aldosterone and ADH)
• Rapid and excessive weight gain

  Raises the suspicion of toxaemia of pregnancy due to excessive fluid retention