Fertilization and Implantation Quiz

Fertilization and Implantation

• Conception, also known as impregnation, initiates pregnancy.
• Following fertilization, the fertilized egg implants in the uterine lining.

Embryonic and Fetal Structures

• Decidua (Uterine Lining): The uterine lining thickens and becomes more vascular under the influence of Human Chorionic Gonadotropin (hCG), preventing its shedding.
• Chorionic Villi: Develop from the single-layer cells of the embryo, extending into the uterine endometrium to form the placenta. Approximately 200 villi form by term. Components include the syncytiotrophoblast and cytotrophoblast (Langhan's layer).
• Placenta: A 15-20cm diameter, 2-3cm deep organ with endocrine functions, producing hCG, progesterone, estrogen, and hPL.
  • hCG: Maintains the uterine lining and suppresses maternal immune response.
  • Progesterone: Maintains pregnancy, reduces uterine contractility. Placental production begins around week 12.
  • Estrogen: Contributes to mammary gland growth and uterine growth.
  • hPL: Growth-promoting and lactogenic hormone; regulates maternal glucose, protein, and fat metabolism.
• Amniotic Membrane and Fluid: The membrane supports and produces amniotic fluid, also producing a phospholipid that initiates prostaglandin formation, potentially triggering labor. Normal amniotic fluid volume at term is 800-1200 mL. Hydramnios (excess fluid) and oligohydramnios (reduced fluid) are noted deviations. Amniotic fluid pH is approximately 7.2.
• Umbilical Cord: Connects the fetus to the placenta, providing a circulatory pathway. Brown fat (for temperature regulation) starts forming in the fetus near the kidneys, sternum, and neck. Vernix caseosa begins to form, covering the skin. Passive antibody transfer from mother to fetus begins; sleep/wake cycles establish.

Fetal Development Timeline

• 24 Weeks: Length 28-36cm; weight 550g; meconium present in rectum; lung surfactant production begins; eyebrows and eyelashes well-defined; eyelids open; pupils react to light; considered a lower-end age of viability with intensive care.
• 28 Weeks: Length 35-38cm; weight 1200g; lung alveoli mature; surfactant in amniotic fluid; testes begin descent; retinal blood vessels form, vulnerable to high oxygen.
• 32 Weeks: Length 38-43cm; weight 1600g; subcutaneous fat deposits; responds to external sounds; Moro reflex present; iron stores develop.
• 36 Weeks: Length 42-48cm; weight 1800-2700g; glycogen, iron, carbohydrate, and calcium stores deposited; additional subcutaneous fat; sole of foot has minimal creases; lanugo diminishes; most fetuses are in vertex presentation.
• 40 Weeks: Length 48-52cm (crown-rump 35-37cm); weight 3000g; active kicking; fetal hemoglobin converts to adult hemoglobin (about 20% adult at birth); vernix caseosa fully formed; fingernails extend beyond fingertips; foot creases cover at least two-thirds of the sole.

Assessing Fetal Growth and Development

• Health History: Essential for assessment.
• McDonald's Rule: Symphysis-fundal height measurement estimates fetal growth during mid-pregnancy: at the symphysis pubis at 12 weeks, umbilicus at 20 weeks, xiphoid process at 36 weeks.
• Nägele's Rule: Estimates due date by subtracting 3 months from the first day of the last menstrual period and adding 7 days.
• Fetal Movement (Quickening): Typically felt by the mother at 18-20 weeks, peaking at 28-38 weeks; at least 10 movements daily are expected.
• Fetal Heart Rate: 120-160 bpm throughout pregnancy; detectable with Doppler from 10-11 weeks. Assessment methods include Rhythm Strip Testing, Nonstress Testing, Vibroacoustic Stimulation and Contraction Stress Testing.

Pregnancy Signs

• Presumptive Signs: Subjective, experienced by the woman but not verifiable by an examiner.
• Probable Signs: Objective signs verifiable by an examiner, including laboratory tests (pregnancy tests).
• Positive Signs: Diagnostic findings confirming pregnancy.

Reproductive System Changes

• Uterine Changes: Anteflexion, increased size and softness; Braxton Hicks contractions appear. Ballottement is evident at 16-20 weeks.
• Cervical Changes: Softening and increased vascularity.
• Vaginal Changes: Vaginal secretions shift from alkaline (pH>7) to acidic (pH 4-5).
• Feedback Mechanisms: Increased estrogen and progesterone inhibit FSH and LH, preventing ovulation.
• Breast Changes: Increased fullness, tingling, tenderness due to estrogen stimulation; areola darkens and enlarges.

Pregnancy and Specific Patient Populations

• Obese Women: Increased risk of gestational diabetes, pregnancy-induced hypertension, thrombophlebitis, macrosomia in infants; increased difficulty in monitoring fetal heart tones and delivery; more difficult ambulation increasing risk of complications. Caloric intake should not fall below 1500-1800 calories to maintain adequate nutrition.
• Morbidly Obese Women: Increased risk of complications such as gestational diabetes, type 2 diabetes, hypertension, back pain, and thrombophlebitis; prone to sleep apnea. Monitoring the fetus and delivery becomes more difficult. Support hose may be recommended for leg circulation. Cesarean births are more frequent.
• Vegetarian Women: Risk of deficiencies in vitamin B12, calcium, and vitamin D; prenatal vitamins are essential. Lacto-ovo vegetarians, lactovegetarians, and vegans each present specific considerations regarding nutrient intake.