WEEK 11 PREGNANCY & MENOPAUSE

Pregnancy

Fertilization

• Zygote formation occurs when male and female nuclei combine. The zygote contains a unique combination of genetic material from both parents, initiating the development of a new organism.

Cell Division

• After fertilization, the zygote undergoes rapid mitotic cell divisions, known as cleavage. These divisions increase the number of cells without significantly increasing the overall size of the embryo.

Implantation

• Occurs approximately 7 days post-fertilization.

• Involves the blastocyst burrowing into the uterine wall. The blastocyst adheres to the endometrium, and trophoblast cells penetrate the uterine lining, establishing a connection between the maternal and embryonic tissues.

Placenta

• The placenta facilitates the exchange of nutrients and waste between the mother and fetus. Maternal blood is separated from fetal blood by the chorion. This separation ensures that while essential substances are exchanged, the bloodstreams do not mix directly, protecting both mother and fetus. During pregnancy, the mother’s blood volume increases by 45-50% to provide sufficient blood flow to the uterus and placenta, meeting the growing fetus’s needs.

• Structure includes:

  • Endometrium

  • Maternal blood in lacuna

  • Placenta

  • Maternal venule and arteriole

  • Fetal arteriole and venule

  • Chorionic villi

  • Umbilical vein and arteries

  • Umbilical cord

Terminology

• Zygote: The cell formed once the male and female nuclei combine. This single cell contains all the genetic information necessary to develop into a complete organism.

• Blastocyst: The stage during the first 2 weeks of development. The blastocyst consists of an inner cell mass, which will form the embryo, and an outer layer, the trophoblast, which will develop into the placenta.

• Embryo: The stage from 2 to 8 weeks. During this critical period, major organs and systems develop in the embryo.

• Fetus: The stage from week 9 to birth. The fetus undergoes further growth and maturation of organs and systems.

• Length of Pregnancy: Approximately 40 weeks, calculated from the first day of the woman’s last menstrual period.

Pregnancy Hormones

• Human Chorionic Gonadotropin (hCG):

  • Secreted by the blastocyst and placenta. hCG is crucial for maintaining the corpus luteum in early pregnancy.

  • Its presence in urine indicates pregnancy. Home pregnancy tests detect hCG levels in urine to confirm pregnancy.

  • Stimulates the growth of the corpus luteum, doubling its size. This growth ensures continued production of estrogen and progesterone.

  • Leads to increased amounts of estrogen and progesterone. These hormones are essential for maintaining the uterine lining and supporting the developing embryo.

• Relaxin:

  • Secreted by the corpus luteum and placenta. Relaxin is vital for preparing the mother’s body for childbirth.

  • Relaxes the ligaments of the body. This relaxation helps to accommodate the growing fetus and facilitates labor.

• Placenta:

  • Secretes estrogen, which increases water retention and protein synthesis. Estrogen promotes the growth of uterine tissues and prepares the mammary glands for lactation.

  • Secretes progesterone, which promotes smooth muscle relaxation and raises body temperature. Progesterone helps prevent uterine contractions and supports the development of the endometrium.

• After 3 months, the placenta takes over the role of the corpus luteum.

  • Serves as a point of exchange between the fetus and mother. The placenta facilitates nutrient and waste exchange without direct mixing of maternal and fetal blood.

  • Functions as an endocrine gland, secreting hormones to maintain pregnancy. The placenta ensures a stable hormonal environment necessary for the pregnancy to continue.

  • Increased levels of estrogen and progesterone during pregnancy.

Physiological Changes During Pregnancy

• Rationale: To provide a suitable environment for fetal growth, nutrition, and development, and to protect and prepare the mother. These changes ensure that the fetus receives everything it needs and that the mother's body can support the pregnancy.

Maternal Cardiovascular Alterations

• Blood Volume:

  • Increases by 45-50% to accommodate increased blood flow to the uterus and other organs. This increase supports the metabolic demands of the fetus and the expanded maternal tissues.

• Heart Rate:

  • Increases by 15-25% (approximately 15 bpm) at rest. The elevated heart rate ensures adequate circulation to both the mother and the fetus.

• Stroke Volume:

  • Increases by 30% due to increased plasma volume and venous return. Stroke volume is the amount of blood pumped by the heart with each beat.

• Cardiac Output:

  • Increases by 40-50% (approximately 1.5 L) due to increased stroke volume and heart rate. Cardiac output is the total amount of blood pumped by the heart per minute.

• Blood Pressure:

  • Can decrease or remain stable in the 1st and 2nd trimesters, returning to normal by the 3rd trimester. Hormonal changes, particularly increased progesterone, contribute to vasodilation, affecting blood pressure.

• Peripheral Resistance:

  • Increased progesterone causes vasodilation, leading to decreased resistance to flow, which contributes to reduced blood pressure. Vasodilation helps to accommodate the increased blood volume and flow.

• Supine Hypotension Syndrome:

  • Blood pressure falls when lying supine as the uterus compresses the inferior vena cava, decreasing venous return. This compression reduces blood flow back to the heart, causing hypotension.

  • Avoid lying in the supine position, particularly on the left side. Lying on the left side can help alleviate pressure on the inferior vena cava.

• Cardiac Position and Size:

  • The diaphragm is pushed upwards. The enlarging uterus exerts pressure on the diaphragm.

  • The apex of the heart is pushed upwards and laterally. This displacement is a result of the upward pressure on the diaphragm.

  • The heart enlarges by 70-80 mL due to increased venous filling caused by increased plasma volume. This enlargement is a physiological adaptation to handle the increased blood volume.

• The primary objective of these adaptations is to increase oxygen supply to accommodate both the fetus and the mother. Adequate oxygen is crucial for fetal development and maternal health.

Maternal Respiratory Alterations

• Oxygen demand increases. The growing fetus requires a significant amount of oxygen, increasing the mother’s oxygen consumption.

• Increases in:

  • Tidal volume (30-50%). Tidal volume is the amount of air inhaled and exhaled during normal breathing.

  • Inspiratory capacity. Inspiratory capacity is the maximum amount of air that can be inhaled after a normal exhalation.

  • Minute volume (20-50%). Minute volume is the total amount of air inhaled or exhaled per minute.

  • Oxygen consumption (absolute). The mother’s body requires more oxygen to support both her and the fetus.

• Decreases in:

  • Expiratory reserve volume. Expiratory reserve volume is the amount of air that can be forcefully exhaled after a normal exhalation.

  • Residual volume. Residual volume is the amount of air remaining in the lungs after a maximal exhalation.

  • Displacement of diaphragm superiorly. The enlarging uterus pushes the diaphragm upwards.

  • Airway resistance

• These changes facilitate more efficient gas mixing. This efficiency ensures that the mother can meet the increased oxygen demands of pregnancy.

Maternal Renal Alterations

• As a result of increased plasma volume:

  • Kidneys enlarge (volume increases). The kidneys work harder to filter the increased blood volume.

  • Increases in:

    • Renal blood flow (30-50%). More blood flows through the kidneys to filter waste products.

    • Glomerular filtration rate (50%). This rate measures how well the kidneys are filtering blood.

  • Increased urination. The increased blood flow and filtration rate lead to more frequent urination.

  • Evidence of glucosuria during pregnancy is possible due to less efficient tubular reabsorption, but it is not necessarily an indication of diabetes. Glucose may be present in the urine because the kidneys may not be able to reabsorb all the glucose from the filtered blood.

Thermoregulation

• During pregnancy, the metabolic rate increases, leading to increased heat production. The body’s metabolism speeds up to support fetal growth, generating more heat.

• The body dissipates additional heat through increased ventilation and skin blood flow. Increased breathing and blood flow to the skin help the mother stay cool.

• Considerations include staying hydrated and avoiding high environmental temperatures. Proper hydration and avoiding heat exposure can help prevent overheating.

Maternal Endocrine Changes

• Anterior Pituitary:

  • Increased plasma concentrations of Prolactin. Prolactin stimulates milk production in the mammary glands.

  • The placenta produces CRH and ACTH. These hormones regulate stress responses and adrenal function.

  • GH, LH, FSH are suppressed. These hormones are suppressed to prevent further ovulation and support the pregnancy.

• Posterior Pituitary:

  • Increased number of oxytocin receptors. Oxytocin plays a crucial role in uterine contractions during labor and milk ejection during breastfeeding.

• Thyroid function increases. The thyroid gland produces more hormones to support the increased metabolic rate.

Physical Changes

• Increased weight gain to the anterior. The growing fetus and uterus cause a shift in the center of gravity.

• Ligament Laxity - Relaxin. Relaxin causes ligaments to loosen, which can lead to joint instability.

• Joint mobility (hypermobility). Joints become more flexible to accommodate the growing fetus and prepare for childbirth.

• The center of gravity moves forward. This shift can affect balance and posture.

• Increased weight of the uterus and breasts. These changes contribute to the overall weight gain during pregnancy.

• Increased loading of joints. Additional weight puts more stress on the joints, particularly in the lower body.

Pelvic Floor

• A layer of muscles that support the pelvic organs (uterus, bladder, bowel). The pelvic floor muscles provide essential support for the pelvic organs.

• Muscles can weaken, leading to urinary incontinence or organ prolapse. Weakened muscles can result in various pelvic floor disorders.

Menopause

• Cessation of the menstrual cycle, typically between 40-60 years of age. Menopause marks the end of a woman’s reproductive years.

• Why: Remaining number of follicles is small; follicles left are less sensitive to FSH and LH; reduced amounts of oestrogen and progesterone. The ovaries become less responsive to hormones that stimulate ovulation.

• Symptoms include uncomfortable sweating (hot flushes), anxiety, fatigue, and emotional disturbances. These symptoms are primarily due to hormonal changes.

Clinical Perspective

• Post-menopausal Osteoporosis:

  • Affects 1 in 3 women. Osteoporosis is a common condition characterized by reduced bone density.

  • Reduction in bone mineral density due to hormonal factors. Decreased estrogen levels significantly impact bone health.

  • Reduced estrogen leads to increased bone loss. Estrogen normally helps to protect bone density, so its decline accelerates bone loss.

  • Increased risk of fractures. Weaker bones are more susceptible to fractures, particularly in the hip, spine, and wrist.