Fertilization Process Overview

Fertilization

• Occurs when a single sperm cell penetrates the ovum's outer layer
• Typically happens during or after ovulation
• One sperm fertilizes the ovum, preventing others from entering
• The sperm and ovum nuclei merge, each containing 23 chromosomes, forming a single nucleus with 46 chromosomes
• This process creates a zygote, the first cell of the developing embryo, with a unique combination of DNA from both parents
• Occurs in the ampulla, the outer third of the fallopian tube
• The zygote divides as it moves towards the uterus, where it implants into the uterine lining
• The sex of the embryo is determined by the sperm's sex chromosome:
  • Ovum always carries an X chromosome
  • Sperm carries either an X or Y chromosome
  • XX results in a female
  • XY results in a male

Process of Fertilization

• 300 million sperm cells enter the vagina during intercourse
• Many sperm die in the vagina's acidic environment or flow out
• Sperm passes through the cervix, which remains open for a few days during ovulation
• Sperm swims through cervical mucus, many die in the process
• Some sperm reach the fallopian tube, where fertilization takes place
• The zygote, a single cell, is swept by cilia towards the uterus
• The zygote implants itself in the uterine lining

Fertilization and Implantation Definitions

• Fertilization: The process of a sperm cell merging with an egg cell to form a zygote, generally occurring in the fallopian tube.
• Implantation: The stage where the fertilized egg (blastocyst) attaches to the uterine wall and establishes a connection with the mother's blood supply.

Nidation

• The embedding of the blastocyst into the uterine lining (endometrium)
• The blastocyst burrows into the lining, allowing it to receive nutrients and oxygen from the mother
• Essential for the embryo's survival and growth

Process of Implantation

• Implantation occurs over several days, not instantaneously
• The zygote travels down the fallopian tube to the uterine cavity
• Timeline:
  • Day 5: ZYgote develops into a blastocyst
  • Days 6-7: Blastocyst begins to make contact with the uterine lining
  • Days 7-8: Blastocyst attaches itself to the endometrial lining
  • Days 9-10: Blastocyst embeds deeply into the uterine lining

Placenta

• A temporary organ connected to the fetus via the umbilical cord
• Develops within the uterine lining, providing nourishment and oxygen to the fetus
• Helps remove waste products from the fetal blood
• Functions:
  • Oxygen and Carbon Dioxide Exchange: Oxygen from the mother's blood flows through the placenta to the fetus, while carbon dioxide moves from the fetal blood to the mother's blood for elimination
  • Nutrition: The placenta transfers essential nutrients from the mother to the fetus such as glucose, amino acids, fatty acids, vitamins, and minerals.
  • Waste Removal: Removes waste products produced by the fetus, including urea and creatinine.
  • Protection: Acts as a barrier, filtering out many harmful substances and pathogens that could harm the fetus. Although it is not a complete barrier, substances like medications, alcohol, and certain viruses can still pass through.

Umbilical Cord

• Connects the fetus to the placenta
• Contains one vein and two arteries (AVA)
• Transports oxygen and nutrients to the fetus and removes waste products
• Wharton's jelly: a gelatinous substance within the cord:
  • Provides structure and support for blood vessels
  • Cushions and protects blood vessels from compression and kinking, ensuring continuous blood flow between the fetus and mother
  • Helps maintain the integrity of the umbilical cord

Gestational and Fertilization Age

• Gestational age: Age of the fetus or pregnancy calculated from the first day of the last menstrual period (LMP). Expressed in weeks and used to estimate the due date and assess fetal development.
• Fertilization age (conception age): Age of the fetus or pregnancy calculated from the day of conception (fertilization). Typically about two weeks less than gestational age because gestational age is calculated from the first day of the LMP, which is approximately two weeks before conception occurs.

Pregnancy Nomenclature

• G: Number of pregnancies
• P: Number of deliveries
• T: Number of term deliveries
• P: Number of preterm deliveries
• A: Number of abortions
• L: Number of living children
• M: Number of multiple births

Expected Date of Confinement/Delivery (EDC/EDD)

• Calculated by adding 7 days and 1 year to the first day of the LMP and subtracting three months.

### Signs of Pregnancy

• Presumptive (Subjective):
  • Amenorrhea (no period)
  • Nausea (with or without vomiting)
  • Breast enlargement and tenderness
  • Fatigue
  • Poor sleep
  • Back pain
  • Constipation
  • Food cravings and aversions
  • Mood changes/”mood swings”
  • Heartburn (increased levels of progesterone leading to the relaxation of the lower esophageal sphincter causing stomach acid to flow back into the esophagus leading to heartburn)
  • Nasal congestion (increased levels of estrogen cause mucosal edema)
  • Shortness of breath
  • Lightheadedness
  • Elevated basal body temperature (BBT)
  • Spider veins
  • Reddening of the palms
• Probable (Objective):
  • Increased frequency of urination
  • Soft cervix
  • Abdominal bloating/enlargement
  • Mild uterine cramping/discomfort without bleeding
  • Increased skin pigmentation in the face, stomach, and/or areola
• Positive:
  • Fetal heartbeat
  • Ultrasound visualization of embryo or fetus

Goals of Prenatal Care

• Safe birth/delivery
• Health promotion
• Self-care
• Provide physical care
• Provide anticipatory guidance

Role of the Nurse

• Physical assessment
• Identify and reevaluate risk factors
• Teach self-care
• Nutrition counseling
• Promote family’s adaptation to pregnancy

Prenatal Visits Schedule

• Every 4 weeks for the first 28 to 32 weeks
• Every 2 weeks from 32 to 36 weeks
• Every week from 36 to 40 weeks

Routine Lab Tests

• Blood grouping
  • Identifies mother’s blood type
• Rh factor and antibody screen:
  • Checks if mother is Rh-positive or Rh-negative
  • Checks for antibodies which could affect the baby
• CBC:
  • Evaluates overall health measuring RBCs, WBCS, hemoglobin, hematocrit, and platelets.
• Hemoglobin and Hematocrit (H&H):
  • Measures the levels of hemoglobin and the percentage of RBCs, assessing for anemia
• VDRL, RPR, or STS:
  • Screens for syphilis, an infection that could be passed to the baby if untreated
• Rubella Titer:
  • Checks immunity to rubella (German measles); if the mother is not immune, exposure during pregnancy could cause birth defects
• Tuberculosis (TB) skin test:
  • Screens for tuberculosis
• Hemoglobin electrophoresis:
  • Identifies hemoglobinopathies like sickle cell disease or thalassemia, both of which can be passed to the baby
• HIV screen:
  • Screens for HIV infection, which could be transmitted to the baby.

This quiz covers the essential steps of fertilization, detailing how a sperm cell penetrates the ovum and the subsequent formation of a zygote. Understand the significance of chromosomes and the determination of the embryo's sex. Test your knowledge of this fundamental biological process.