Prenatal Development and Diseases Associated with Pregnancy Flashcards
Fertilization
Union of sperm and ovum occurs in fallopian tube; possible when sperm are present in fallopian tubes at the time egg is expelled at ovulation
Early Development: Fertilized Ovum
Fertilization occurs in fallopian tube
* Sperm contain genetic material and enzymes for penetration
* Zygote develops into a small ball of cells
* Fluid accumulates to form blastocyst
* Inner cell mass forms embryo
* Trophoblast forms placenta and membranes
* Blastocyst begins to differentiate
Stages of Prenatal Development
Preembryonic period; Embryonic period; Fetal period
Preembryonic period
First 3 weeks after fertilization
* Blastocyst becomes implanted, and inner mass cell differentiates into three germ layers to eventually form specific tissues within embryo
Embryonic period
Third through seventh week
* Begins to assume a human shape
* All organ systems are formed
* Very critical period of development
Fetal period
Eighth week to term
* Fetus continues to grow
* No major changes in basic structure
* Subcutaneous fat accumulates; fills body shortly before delivery
Gestation
Total duration of pregnancy from fertilization to delivery
* Dated from time of conception: 38 weeks
* Dated from first day of last menstrual period (date of ovulation unknown): 40
weeks
* First day of the calculation is 2 weeks before the date of conception
* May be expressed as 280 days
Decidua
Endometrium of pregnancy
Decidua basalis
Under chorionic vesicle
Decidua capsularis
Over chorionic vesicle
Decidua parietalis
Lines rest of the uterus
Chorion laeve
Superficial, smooth chorion
Chorion frondosum
Bushy chorion
Amniotic sac
Enclosed within chorion, forms a protective environment
Yolk sac
Forms intestinal tract
Functions of the placenta
- Provides oxygen and nutrition for fetus
- Has endocrine function: Synthesizes hormones (estrogen, progesterone, protein hormones)
- Human placental lactogen (HPL)
- Human chorionic gonadotropin (HCG)
Placenta
Fetus connected to placenta by umbilical cord; Double circulation of blood
Fetoplacental circulation
From fetus to villi
Uteroplacental circulation
Maternal blood circulates around villi
Amniotic Fluid
Produced by filtration and excretion
* Filtration from maternal blood early in pregnancy
* Fetal urine later in pregnancy
Polyhydramnios
Increased volume of amniotic fluid
* Fetus unable to swallow and fluid accumulates (anencephaly)
* Fluid is swallowed but not absorbed due to congenital obstruction of fetal upper intestinal tract
Oligohydramnios
Reduced volume of amniotic fluid
* Fetal kidneys failed to develop and no urine is formed
* Congenital obstruction of urethra does not allow urine to form amniotic fluid
Hormone-Related Conditions Associated with
Pregnancy
Nausea and vomiting during early pregnancy
* Estrogen increases rapidly early in pregnancy - Causes nausea and vomiting
Hyperemesis gravidarum
* Excessive vomiting, more prolonged and severe than normal; Weight loss and dehydration require treatment
Gestational Diabetes
Pregnancy hormones induce maternal insulin resistance
* Diabetes results from inability to increase insulin secretion to compensate for increased insulin resistance
Hyperglycemia
harmful to the fetus; Diabetes usually relents following delivery
Ectopic Pregnancy
Development of embryo outside the uterine cavity
* Most common site is fallopian tubes
Predisposing factors of Ectopic Pregnancy
- Previous infection of fallopian tubes
- Failure of normal muscular contractions of tubal wall
- Both fallopian tubes predisposed
Consequences of Ectopic Pregnancy
- Rupture of fallopian tube
- Profuse bleeding from torn vessels
- Potentially life threatening to mother
Abnormal Attachment of Umbilical Cord
Velamentous insertion; Placenta previa;
Velamentous insertion
- Cord attached to fetal membranes instead of placenta
- May tear or is compressed during labor
- May be fatal to infant
- No adverse effect on mother
Placenta previa
Placenta attached at lower part of uterus; may cover
cervix
* Causes episodes of bleeding late in pregnancy
* Hazardous to both mother and infant
* Requires delivery by cesarean section
Central placenta previa
Placenta covers entire cervix
Partial placenta previa
Margin of placenta covers cervix
Twin transfusion syndrome
Vascular anastomoses connect placental circulations of identical twins
* One twin is polycythemic and one is anemic
* Tolerated if minor disproportions in blood; if severe, may be fatal to both twins
Vanishing twin
One of the twins dies and is resorbed
Blighted twin
One of the twins dies and persists as degenerated fetus
Fraternal twins
Two separate ova fertilized by two different sperm
Identical twins
Single fertilized ovum splits
Conjoined twins
Variable union between identical twins
Preeclampsia and eclampsia
Toxemia of pregnancy
* Pregnancy-associated elevated blood pressure exceeding 140/90; accompanied by protein in the urine
Eclampsia
Blood pressure exceeding 160/110; may cause convulsions
* Seems to be caused by inadequate blood flow to the placenta
* Causes blood vessel constriction, blood pressure elevation, and clumping of platelets
Hydatidiform mole
hydatid is fluid-filled vesicle; mole is shapeless structure
* Occurs in 80% of affected patients
* Complete mole
* Results from abnormal fertilization of an ovum lacking chromosomes and ovum fertilized by a single sperm bearing an X chromosome that is duplicated to form 46
Complete mole
- Both X chromosomes come from the father
- No embryo develops
- Chorionic villi become cystic structures resembling mass of grapes (complete mole)
Partial mole
- Normal ovum fertilized by two sperm, resulting in a fertilized ovum with three sets of chromosomes (69 chromosomes)
- Embryo forms but does not survive
- Less likely to exhibit aggressive behavior
Invasive mole
- Trophoblastic tissue invades deep into uterine wall
- Occurs in 15% of affected patients
- Aggressive, destructive
Choriocarcinoma
May arise following incomplete removal of invasive or incompletely removed mole
* Masses of proliferating trophoblast may extend into vagina
* Metastasizes to lungs and brain
Treatment of Choriocarcinoma
Curettage, periodic determination of HCG; hysterectomy;
chemotherapy
Hemolytic Disease of the Newborn Pathogenesis
- Sensitization of mother to a blood group antigen in fetal red blood cells
- Mother forms antibodies that cross placenta
- Maternal antibodies damage fetal red blood cells
- Fetus increases blood production to compensate for increased red blood
cell destruction
Less intense hemolytic process
Infant is born alive but moderately or severely anemic
Mild disease
Infant appears normal at birth then becomes anemic and jaundiced, develops edema
Hydrops fetalis
Severe anemia causes heart failure and impaired hepatic plasma protein synthesis
* Results in edema
* Hemolytic process is extremely severe, causing death
* Infant dies in uterus during last trimester
Rh Hemolytic Disease
Most cases: Rh-negative mother and Rh-positive infant
* Consists of a series of allelic genes that determine multiple Rh antigens on red cells
* Mother sensitized to foreign antigen in infant’s cells and forms anti-D antibodies that cross placenta into infant’s blood
Rh positive
Red cells contain D (Rho) antigen
* May be homozygous (genotype DD)
* May be heterozygous (genotype Dd)
Rh negative
Red cells lack D (Rho) antigen
* Genotype dd
Treatment of Rh Hemolytic Disease
- Exchange transfusion
- Fluorescent light therapy for hyperbilirubinemia
- Intrauterine fetal transfusion
Prevention of Rh Hemolytic Disease
Rh immune globulin administered to mother
* Contains gamma globulin with Rh antibody
* Given within 72 hours after delivery of Rh-positive infant
* Rh antibody coats Rh antigen sites on surface of fetal red cells in maternal circulation to reduce sensitization
ABO Hemolytic Disease Pathogenesis
Mother is type O (has anti-A and anti-B antibodies in her serum) and infant is type A or type B
* Maternal anti-A and anti-B antibodies attach to fetal red cells
* Can occur in first ABO-incompatible pregnancy due to preexisting anti-A and anti-B antibodies
ABO Hemolytic Disease Manifestations
Milder disease than Rh hemolytic disease because fetal A and B antigens are not as well developed, unlike in adult cells; antibodies do not attach as firmly to fetal cells
* Complications: Anemia, hyperbilirubinemia, kernicterus
* Excess unconjugated bilirubin from red cell breakdown
Treatment of ABO Hemolytic Disease
Control hyperbilirubinemia by fluorescent light therapy
* Exchange transfusion not usually required
