implantation and fertlization

FERTILIZATION AND IMPLANTATION

By dr. Mona Ahmed

Introduction: Post-Ovulation Preparation

Endometrial Changes

After ovulation the cells of the dominant follicle & CL produces large amounts of progesterone which prepares the endometrium to support a pregnancy.

Fertilization Process

• Involves the fusion of two haploid gametes with 23 chromosomes each to produce a zygote that contains 46 chromosomes
• Fertilization generally occurs in the fallopian tube and generally within one day of ovulation.
• Both sperm and egg can show their vitality only to a limited period. Sperm is alive for 48-72 hours in a female reproductive system whereas the egg can be fertilized for 24 hours.

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Implantation Process

• After fertilization the zygote travels down the fallopian where it becomes a morula.
• Once it reaches the uterus, the morula becomes a blastocyst.
• The blastocyst then burrows into the uterine lining, a process called implantation.

Hormonal Regulation: Human Chorionic Gonadotrophin (hCG)

hCG Secretion and Physiological Role

The implanted blastocyst secretes human chorionic gonadotrophin (hCG):

• ‘rescue CL from luteolysis to maintain progesterone secretion.
• prevent menstruation.
• and support the early conceptus (for approximately 8 weeks).
• after which the early placental tissue becomes the main source of progesterone.

hCG Detection in Pregnancy

• hCG can be detected in the urine in sensitive pregnancy tests 1 or 2 days before the expected date of menstruation.
• Most women delay taking a pregnancy test until after a missed period.

Visualizing Early Pregnancy

Ultrasound Detection of Gestational Sac and Embryo

• A transvaginal ultrasound scan (TVUSS) can detect an early intrauterine gestational sac, the first sign of a normal pregnancy, at around 5 weeks’ gestation.

• A few days later a circular yolk sac can be seen within the gestational sac, and the embryonic fetus can usually be identified after 5.5 weeks’ gestation.

•  The fetal heartbeat may be visible as early as 6 weeks’ gestation.

Ultrasound Imaging Parameters

#CC VID

Embryonic Structure Post-Implantation

Clinical Manifestations of Implantation

Symptoms and Signs

• Gastrointestinal disorders
• Breast swelLLING
• Nausea
• Implantation bleeding
• Increased urge to urinate

hCG (human chorionic gonadotropin)

• Primarily produced by syncytiotrophoblasts.

• Detected from 6 days after fertilization; forms basis of modern pregnancy testing.

• Concentrations reach a peak at 10–12wks gestation, then plateau only after 13 weeks until remainder of the pregnancy. - beyond 13 weeks is abnormal, may be due choriocarcinoma Molar pregnancy can produce very high hCG levels, which often result in nausea and vomiting—symptoms similar to those of a normal pregnancy.

Effect

• continuation of pregnancy
• Maintenance of the corpus luteum graviditatis
• Stimulation of progesterone and estrogen synthesis of the corpus luteum graviditatis

Detailed Characteristics and Effects of hCG

• ✓ Primarily produced by syncytiotrophoblasts.
• ✓ Detected from 6 days after fertilization; forms basis of modern pregnancy testing.
• ✓ Concentrations reach a peak at 10-12wks gestation, then plateau for remainder of the pregnancy.
• Effect
  • ✓ continuation of pregnancy
  • ✓ Maintenance of the corpus luteum graviditatis
  • ✓ Stimulation of progesterone and estrogen synthesis of the corpus luteum graviditatis

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Comparison Table: Maternal Complications

Condition	Key Diagnostic Features	Critical Management	Unique Risks
Hyperemesis Gravidarum	>5% weight loss, dehydration, ketonuria, no other cause	IV fluids (RL/NS), thiamine first, then B6 + doxylamine	Wernicke encephalopathy, fetal growth restriction
Cervical Insufficiency	Painless dilation <24w, history of 2nd-trimester loss	Cerclage (McDonald/Shirodkar), vaginal progesterone	Preterm birth, PPROM
Chorioamnionitis	Maternal fever >38°C + fetal tachycardia/malodorous fluid	IV ampicillin + gentamicin (+ clindamycin if C-section)	Neonatal sepsis, maternal DIC
Pemphigoid Gestationis	Periumbilical blisters/itching, “herpetiform” lesions	Topical/systemic glucocorticoids	Preterm labor, fetal rash
Polymorphic Eruption (PEP)	Pruritic papules in striae, spares umbilicus	Low-potency steroids, antihistamines	None (benign)
Pregnancy Luteoma	Solid ovarian mass, maternal/fetal virilization	Expectant management (resolves postpartum)	Premature labor (if large)

Essential Hyperemesis Takeaways:

• Emergency Protocol:
  1. Rule out moles/infection → Ultrasound, β-hCG, U/A.
  2. IV Fluid: LR/NS (not dextrose initially).
  • Thiamine (100mg IV) → before any glucose to prevent Wernicke’s.
  • Antiemetics: Pyridoxine (B6) + doxylamine (1st-line), then ondansetron.
• Diet: Small dry-carb meals; avoid triggers (strong smells, iron supplements).
• Discharge Criteria: Tolerating oral intake, ketonuria resolved, weight stable.