Embryonic & Fetal Development and Pregnancy Changes

Embryonic and Fetal Development

• Conception: Fertilization of ovum by sperm in the oviduct.

• Zygote Formation: Genetic information from ovum and sperm merge to form zygote; undergoes mitotic divisions.

• Implantation: Zygote implants in uterine wall approximately $1$ week after fertilization.

• Differentiation: Inner cell mass becomes fetus; outer cell mass (trophoblast) forms embryonic membranes (amnion, placenta).

• Embryonic Stage ($3$ to $8$ weeks): Critical period of organogenesis; rapid cell division and differentiation form basic organ systems. By end of $8$ weeks, all organs are formed (e.g., heart beating at $4$ weeks).

• Teratogens: Substances that cause developmental abnormalities (drugs, viruses, alcohol, radiation).

  • Exposure during embryonic stage causes major widespread damage and congenital abnormalities.

  • Maternal Rubella: In $1$st trimester, affects $90\%$ of cases, causing spontaneous abortion or major anomalies.

  • Erythema Infectiosum: In $1$st half of pregnancy, causes severe fetal anemia and potential death.

  • Cigarette Smoking: Linked to low birth weight, irritability, stillbirth, placenta previa, abruptio placentae.

  • Alcohol: Causes Fetal Alcohol Syndrome, impairing neurological/intellectual development, causing physical characteristics, and growth retardation.

• Folic Acid: Increased intake reduces neural tube defects (e.g., spina bifida).

• Fetal Stage (After $8$ weeks): Most organs complete basic formation; teratogens have less effect. Continued growth and maturation (e.g., lungs in last trimester).

• Viability: Fetus may survive outside uterus as early as $22$ to $23$ weeks after conception.

• Twin Types:

  • Monozygotic (Identical): Developing embryo divides to form $2$ genetically identical embryos ($1:100$ births).

  • Dizygotic (Fraternal): Two ova fertilized by two different sperm, resulting in $2$ genetically dissimilar embryos.

Physiologic Changes During Pregnancy

• Hormonal Changes: Increased estrogen and progesterone (from placenta) are essential for uterine development, pregnancy maintenance, and breast preparation. Increased thyroid activity raises maternal metabolism.

• Reproductive System Changes:

  • Uterus: Tremendous size increase (hypertrophy, hyperplasia, increased vascularity). Exerts pressure on bladder/bowel (altered elimination) and diaphragm (shortness of breath).

  • Cervix/Vagina: Increased vascularity (Goodell and Chadwick signs), softened tissues. Cervical mucus forms protective plug. Increased, more acidic vaginal secretions (pH $3.5$ to $6.0$) predispose to yeast infections.

  • Breasts: Enlarge, ducts and glands develop, increased fatty deposits, prominent veins, tenderness.

• Weight Gain and Nutrition: Average weight gain of $11$ to $14$ kg ($25$ to $30$ lb). Increased demand for protein, carbohydrates, fat, vitamins, and minerals. Fetus stores iron in last trimester. Adequate calcium is crucial for fetal bones.

• Digestive System Changes:

  • Nausea and Vomiting: Common in $1$st trimester due to hormonal changes.

  • Hyperemesis Gravidarum: Severe, uncontrollable vomiting leading to dehydration and electrolyte imbalances, requiring hospitalization.

  • Progesterone effects: Relaxation of smooth muscle causes decreased motility, slower stomach emptying, heartburn (reflux), bloating.

  • Constipation: Common due to decreased motility and iron supplements; can lead to hemorrhoids. High-fiber diet recommended.

• Musculoskeletal Changes: Pelvic joints relax, causing loss of stability and waddling gait. Increased abdominal weight shifts center of gravity, leading to lordosis (increased lumbar curvature) and backache.

• Cardiovascular Changes:

  • Blood Volume: Greatly increased (fluid and erythrocytes) to meet fetal metabolic needs.

  • Vascular Resistance: Tends to decrease due to increased progesterone.

  • Blood Pressure: Drops slightly in $1$st two trimesters, then returns to normal in the last.

  • Edema/Congestion: Increased blood volume leads to nasal congestion and gingivitis.

  • Anemia: Physiologic anemia (dilutional) occurs due to relatively greater increase in fluid volume; increased iron intake is often required.

  • Varicose Veins: Frequently develop due to uterine pressure and predisposition. Elevate legs and avoid restrictive clothing.

  • Supine Position: Heavy uterus can compress inferior vena cava, decreasing venous return and cardiac output, leading to hypotension.

Diagnosis of Pregnancy

• Laboratory Diagnosis: Based on presence of human chorionic gonadotropin (hCG) in maternal plasma or urine.

• Positive Signs: Fetal heartbeat (auscultation/ultrasound), fetal movement (detected by others), visualization of fetus (ultrasound).

• Estimated Date of Delivery (EDD/EDB): Calculated using Nägele's rule (subtract $3$ months from LMP, add $7$ days).

• Gestation: Length of time since $1$st day of LMP ($280$ days or $40$ weeks). Gestational age is $2$ weeks longer than actual fetal age.

• Gravidity: Number of pregnancies (e.g., primigravida = $1$st pregnancy).

• Parity: Number of pregnancies reaching fetal viability (approximately $22$ weeks).

• Amniocentesis: Withdrawal of amniotic fluid/fetal cells after $14$ weeks for chemical content and chromosome analysis; recommended for abnormalities or maternal age over $35$.

• Chorionic Villus Sampling: Earlier procedure for chromosomal examination in high-risk clients.

Potential Complications of Pregnancy

• Ectopic Pregnancy: Fertilized ovum implants outside the uterus (most commonly in fallopian tube). Can lead to rupture, severe hemorrhage, or peritonitis; requires prompt surgical treatment.

• Preeclampsia and Eclampsia (Pregnancy-Induced Hypertension - PIH):

  • PIH: Persistently elevated blood pressure (>140/90) after $20$ weeks, resolving postpartum. Risks include vessel damage, stroke, heart failure, and placental complications.

  • Preeclampsia: Higher BP, kidney dysfunction (proteinuria, weight gain, generalized edema). May involve HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets) or DIC.

  • Eclampsia: Extremely high BP, generalized seizures, or coma. Requires immediate hospitalization.

• Gestational Diabetes Mellitus (GDM): Increased glucose intolerance during pregnancy. Higher risk of fetal abnormalities (if high glucose in $1$st trimester), stillbirth, increased birth weight. Diet and insulin control are crucial; oral hypoglycemics are contraindicated.

• Placental Disorders:

  • Placenta Previa: Placenta implanted in lower uterus or over cervical os. Characterized by painless bright red bleeding as uterus expands.

  • Abruptio Placentae: Premature separation of placenta from uterine wall. Causes dark red bleeding (may be concealed) and abdominal pain; occurs most often in last trimester.

• Blood Clotting Disorders:

  • Thrombophlebitis/Thromboembolism: Blood clots, common postpartum in leg or pelvic veins, due to stasis or increased coagulability. Can lead to pulmonary embolus. Early ambulation is encouraged.

  • Disseminated Intravascular Coagulation (DIC): A serious complication (e.g., of abruptio placentae or preeclampsia) involving increased clotting mechanism activation, leading to consumption of clotting factors and subsequent hemorrhage.

• Rh Incompatibility: Occurs when an Rh-negative mother carries an Rh-positive fetus. Maternal antibodies destroy fetal red blood cells (hemolytic disease of the newborn), causing severe anemia, heart failure, jaundice, and potential neurological damage.

  • Prevention: Administering Rh immunoglobulin (RhoGAM) to the mother within $72$ hours of delivery prevents sensitization.

• Infection:

  • Puerperal Infection (Childbed Fever): Reproductive tract infection postpartum. Can affect lacerations, episiotomy sites, or the uterine lining (endometritis).

  • Symptoms: Fever, vomiting, lower abdominal pain, foul-smelling vaginal discharge. Can spread to pelvic cellulitis or peritonitis (a serious complication).

Adolescent Pregnancy

• Carries increased risks due to the mother's immature body and various lifestyle factors.

• Nutritional Needs: High demands for both adolescent's growth and fetal development are often inadequately met.

• Pelvic Structure: May be too small for fetal head, increasing labor complications.

• Common Complications: Anemia, low birth weight, preterm birth, and Pregnancy-Induced Hypertension (PIH).

• Increased Risk Factors: Maternal smoking, alcohol use, and drug intake are more prevalent.

• Support: Psychosocial support and counseling are essential for positive outcomes.