Abnormal Implantation Quiz

Abnormal Sites of Implantation

• Ectopic pregnancy: implantation occurs outside the uterus.
  • Uterine tube (tubal pregnancy): most common.
  • Abdominal cavity: rare.
  • Ovary (ovarian pregnancy): very rare.
• Placenta previa: placenta develops in the lower segment of the uterus near the internal os.

Types of Placenta Previa

• Low-lying placenta previa: placenta is in the lower part of the uterus but doesn't reach the internal os.
• Marginal placenta previa: placenta's edge reaches the margin of the internal os.
• Partial placenta previa: placenta partially covers the internal os.
• Complete placenta previa: placenta completely covers the internal os.

Normal Fertilization

• Occurs in the ampulla of the uterine tube.

Second Meiotic Division of Secondary Oocyte

• Completes at fertilization.

Implantation Stage

• Blastocyst stage is crucial for implantation.

Result of Fertilization

• Restoration of the diploid number of chromosomes.

Acrosomal Reaction

• Removal of the cholesterol coat and glycoprotein coat covering the acrosome.

Pregnancy Detection Hormone

• Human Chorionic Gonadotrophin (hCG) is used for pregnancy detection.

Preovulatory Phase of Ovarian Cycle

• Influenced by follicle-stimulating hormone (FSH).

Postovulatory Phase of Ovarian Cycle

• Influenced by progesterone.

Embryonic Folding & Its Effects

• Primitive gut: forms foregut, midgut, and hindgut.
• Definitive yolk sac: smaller than the primitive yolk sac.
• Yolk sac stalk: connects the yolk sac to the embryo.

Ectodermal Derivatives

• Epidermis

Endodermal Derivatives

• Urinary bladder

Mesodermal Derivatives

• Dermis

Gastrulation

• Process of forming the three germ layers (ectoderm, mesoderm, endoderm).

Bilaminar Areas of the Embryo

• Buccopharyngeal membrane
• Septum transversum
• Cardiac area

Placenta Components

• Fetal part: formed by the chorion frondosum.
• Maternal part: formed by the decidua basalis.

Chorion Parts

• Chorion frondosum: forms the fetal part of the placenta.
• Chorion laeve: villi degenerate.

Decidua

• Decidua basalis: lies over the chorionic frondosum.
• Decidua capsularis: covers the chorion laeve.
• Decidua parietalis: lines the remaining part of the uterine cavity.

Internal Structure of Placenta

• Chorionic villi: filled with fetal blood.
• Intervillous spaces: filled with maternal blood.
• Placental septa: divide the maternal surface into 15-20 cotyledons.

Placental Barrier

• Early pregnancy: formed by the endothelium of fetal vessels and extra-embryonic mesoderm.
• Late pregnancy: formed by the endothelium of fetal vessels, cytotrophoblast, and syncytiotrophoblast.

Full-Term Placenta

• Disc-shaped:
  • Diameter: 15-25 cm
  • Thickness: 3 cm
  • Weight: 500 g.

Full Term Placenta Surfaces

• Fetal surface: formed by the chorion frondosum.
• Maternal surface: formed by the decidua basalis.

Placental Anomalies

• Shape anomalies:
  • Diffuse placenta (placenta membranacea): all fetal membranes remain covered by chorionic villi.
  • Accessory placenta (succenturiate placenta): a main placenta with a small accessory lobe.
  • Bidiscoidal placenta: two disc-like equal parts.
• Invasion anomalies:
  • Placenta accreta: placenta grows superficially into the myometrium.
  • Placenta increta: placenta grows into the myometrium.
  • Placenta percreta: placenta invades the myometrium and perimetrium.
• Attachment anomalies:
  • Placenta previa: placenta develops in the lower segment of the uterus near the internal os.
• Chord anomalies:
  • Very long umbilical cord: may wind around the fetus's neck and cause death.
  • Very short umbilical cord: may cause premature separation of the placenta.
• Umbilical cord anomalies:
  • Eccentric attachment.
  • Marginal attachment (battledore placenta).
  • Velamentous attachment: cord ends in the membranes surrounding the placenta.
• False knots: caused by excessive tortuosity of umbilical vessels.
• True knots: rare but dangerous; they obstruct blood flow in umbilical vessels, leading to fetal death.
• Single umbilical artery: one umbilical artery instead of two.

Twins

• Dizygotic (fraternal):
  • Incidence: 70% of twins.
  • Mechanism: two ova released simultaneously.
  • Characteristics: 2 placentae, 2 chorionic cavities, 2 amniotic cavities.
  • Sex: can be the same or different.
• Monozygotic (identical):
  • Incidence: 30% of twins.
  • Mechanism: splitting of a single embryo.
  • Characteristics: can share no, some, or all their fetal membranes.
  • Sex: always the same sex.

Siamese (Conjoined) Twins

• Fused monozygotic twins due to incomplete separation of the embryonic disc.
• Types:
  • Craniopagus: fusion of two heads.
  • Thoracopagus: fusion at the thoracic region.
  • Pygopagus: fusion at the pelvic region.

Prenatal Diagnosis Techniques

• Non-invasive:
  • Maternal serum screening: measures levels of alfa-fetoprotein (AFP), unconjugated estriol (uE3), and hCG.
  • Ultrasound.
• Invasive:
  • Amniocentesis: sampling amniotic fluid; preferred after 16 weeks gestation.
  • Chorionic villus sampling (CVS): sampling chorionic villi; preferred at 10 weeks gestation.

Maternal Serum Screening

• AFP:
  • Increased: neural tube defects.
  • Decreased: Down syndrome.
• uE3:
  • Increased: throughout pregnancy.
  • Decreased: Down syndrome.
• hCG:
  • Increased: Down syndrome.
  • Decreased: Down syndrome.

Invasive Tests

• Amniocentesis:
  • Withdrawal of amniotic fluid for analysis of bilirubin levels, AFP, and fetal cells.
• Chorionic villus sampling (CVS):
  • Sampling of chorionic villi for DNA analysis and chromosomal abnormality detection.

Fetal Part of Placenta

• Chorion frondosum

Maternal Part of Placenta

• Decidua basalis

Polyhydramnios Causes

• Diabetic mother
• Fetus with renal agenesia
• Fetus with obstructive uropathy

Oligohydramnios Causes

• Fetus with esophageal atresia
• Fetus with renal agenesia