Maternal Physiological Adaptations in Human Pregnancy

Maternal Physiological Adaptations in Pregnancy

• Overview of Physiological Changes
  • All maternal organ systems experience physiological changes during pregnancy.
  • Most systems return to normal after delivery.
  • Changes are more pronounced in multiple fetal pregnancies than in single fetal pregnancies.
  • Major adaptations in anatomy, physiology, and metabolism are required for a successful pregnancy.

Anatomy of the Female Reproductive Tract

• Key Components:
  • Follicles, Oviduct, Ovaries, Corpus luteum, Uterus, Wall of uterus, Endometrium (lining of uterus), Cervix, Vagina

Changes in the Uterus

• Size and Weight:
  • Expands from a pelvic organ to an abdominal organ beyond 12 weeks.
  • Weight increases from 60g to approximately 1000g (20 times original weight).
  • Size changes from 6.5 cm to 32 cm during pregnancy.
• Shape Changes:
  • Elongated to oval (2nd month) to round (mid-gestation) and elongates again at term.
• Causes of Expansion:
  • Growth of the fetus, increase in connective tissue, and blood vessels supplying the uterus.

Changes in the Cervix

• The cervix remains closed during pregnancy.
• Mucus Plug:
  • Forms a protective barrier.
• During labor, the cervix dilates to allow a 10 cm opening for childbirth.
• Cerclage:
  • A procedure to stitch the cervix if it dilates prematurely.

Placenta and Fetal Membranes

• Placenta:
  • Circular, disc-shaped organ that supports fetal development, 15-20 cm in diameter, 2.5 cm thick.
• Fetal Membranes (Amnion and Chorion):
  • Form the amniotic sac, protecting the fetus.
  • Amnion: 0.02 – 0.5 mm thick, no blood or nerve supply.
  • Chorion: Thicker than the amnion, supplying structural support, with no vessels or nerves.

Endocrine Changes

• Hormonal Changes in Pregnancy:
  • Involves interplay of hormones from the fetus, placenta, and mother.
  • At 6-8 weeks, the function shifts from the corpus luteum to the placenta.
• Key Hormones:
  • hCG, progesterone, estrogen, CRH, GnRH, and others influence pregnancy.

Breast Changes

• Breasts enlarge to twice their normal weight, with increased fat deposits and mammary gland growth due to estrogen.
• By 16 weeks, colostrum production begins, leading to lactation preparation.

Lactation Stages

• Mammogenesis: Preparation of the breast for lactation.
• Lactogenesis: Synthesis and secretion of milk.
• Galactokinesis: Ejection of milk.
• Galactopoiesis: Maintenance of milk production.
• Involution: Termination of lactation.

Relaxin and Joint Changes

• Relaxin: Produced by ovaries and placenta to relax ligaments and muscles, aiding in labor.
• Altered Center of Gravity: Changes due to abdominal bulkiness affect posture and may lead to back pain.

Cardiovascular System Adaptations

• Heart Changes:
  • The heart enlarges as a result of hypertrophy, especially in the left ventricle.
• Blood Flow Adjustments:
  • Blood volume increases by about 1.5 liters, impacting overall circulation.

Blood Changes

• Red blood cells increase in mass due to elevated erythropoietin, while plasma volume also increases, leading to hemodilution and decreased hemoglobin concentration.

Immune System Adaptations

• Maternal Immune Tolerance:
  • Changes prevent maternal immune responses against the fetus and placenta, crucial for successful pregnancy.
• Placenta as Immunological Barrier:
  • Functions to protect the fetus while still allowing necessary exchanges between mother and fetus.

Respiratory and Gastrointestinal Changes

• Respiratory System Effects:
  • Changes in lung capacity and airway resistance due to pressure from the growing uterus.
• Gastrointestinal Adjustments:
  • Slower digestion and various gastrointestinal symptoms may occur due to hormone levels and pressure from the uterus.

Metabolic Changes

• Overall Metabolism Increases:
  • Total metabolism increases, affecting carbohydrates, lipids, and protein metabolism to support fetal development.
  • Women require additional caloric intake during pregnancy (around 300 calories/day).

Conclusion

• Summary of Adaptations:
  • Pregnancy leads to various systemic changes to support fetal growth, ensure the health of the mother, and prepare for labor.
  • These changes include cardiovascular, respiratory, immune, and metabolic adaptations that are integral to the development process and eventual delivery.