Chapter 8: Twins

Question 1

Twins

Answer 1

Giving birth to more than one baby.

Question 2

Types of twins

Answer 2

1. Dizygotic (fraternal) twins.
2. Monozygotic (identical) twins.

Question 3

Dizygotic (fraternal) twins cause

Answer 3

Formation of two zygotes by simultaneous ovulation of two oocytes and fertilization by two sperms.

Question 4

Dizygotic (fraternal) twins incidence

Answer 4

1. Commonest type.
2. Represents 0.7-1.1% of the total births.

Question 5

Dizygotic (fraternal) twins features

Answer 5

1. Each embryo implants separately.
2. Each embryo develops its own amnion, chorion, and placenta.
3. Offspring are not identical in shape and may be of some or different sex.

Question 6

Monozygotic (identical) twins cause

Answer 6

Splitting of fertilized ovum at variable stages of development.

Question 7

Monozygotic (identical) twins incidence

Answer 7

0.3-0.4% of total births.

Question 8

Monozygotic (identical) twins features

Answer 8

1. Offspring are identical in shape and sex.
2. Fetal membranes are variable according to the stage at which splitting occurs.

Question 9

Stages at which splitting occurs:

Answer 9

1. Splitting of morula.
2. Splitting of inner cell mass of early blastocyst.
3. Splitting of the embryonic disc of late blastocyst.

Question 10

Splitting of morula

Answer 10

1. Morula divides into two morulae which develop into two separate blastocysts.
2. Each embryo has its own amnion, chorion, and placenta.

Question 11

Splitting of inner mass of early blastocyst

Answer 11

1. Single blastocyst which has 2 inner cell masses.
2. Both embryos have common chorion and placenta.
3. Each embryo has its own amnion.

Question 12

Splitting of embryonic disc of the late blastocyst

Answer 12

1. Single blastocyst which has 2 embryonic discs.
2. Both embryos have a common amnion, chorion, and placenta.

Question 13

Siamese (fused) twins

Answer 13

Occurs due to incomplete split of the embryonic disc.

Question 14

Siamese (fused) twins sites of fusion

Answer 14

1. Craniopagus: head.
2. Thoracopagus: thorax.
3. Pygopagus: pelvis.

Question 15

Success of surgical separation of Siamese twins depends on?

Answer 15

1. Site of fusion.
2. Organs in common between the twins.

Question 16

Twin defects

Answer 16

Twins may suffer from:
1. Increased incidence of prematurity.
2. Low birth weight.
3. High mortality rate.

Question 17

Birth defects

Answer 17

Structural and/or functional disorders present at birth. They are caused by environmental or genetic factors acting independently or together.

Question 18

Risky gestational period

Answer 18

1. Embryonic period: most sensitive time (3rd to 8th week).
2. Fetal period: risk for gross structural defects are decreased, but organ systems may still be affected (9th week to full term).

Question 19

Factors responsible for birth defects

Answer 19

1. Environmental factors (teratogens).
2. Chromosomal abnormalities.
   - Unknown etiology.
   - Multifactorial inheritance.
   - Mutant genes.

Question 20

Environment factors (teratogens)

Answer 20

The effects of teratogens varies according to:
1. Developmental stage at the time of exposure.
2. Dose and duration of exposure of the tertogen.

Question 21

Teratogens factors

Answer 21

1. Infectious agents.
2. Radiations.
3. Drugs and chemicals.
4. Maternal causes.
5. Paternal causes.

Question 22

Infectious agents

Answer 22

1. Viruses.
2. Bacteria.
3. Parasites.

Question 23

Viruses

Answer 23

1. German measles.
2. Cytomegalovirus.
3. Herpes simplex.
4. Varicella.
5. HIV (AIDS).

Question 24

Bacteria

Answer 24

Syphilis

Question 25

Parasites

Answer 25

Toxoplasma

Question 26

Radiation

Answer 26

Ionizing radiation: X-ray and gamma rays.

Question 27

Why does radiation has teratogenic effects?

Answer 27

1. They kill rapidly proliferating cells. 2. They lead to genetic alteration of germ cells with subsequent fetal movements.

Question 28

Drugs and chemicals

Answer 28

1. Most drugs, especially in the first 3 months. 2. Alcohol and nicotine.

Question 29

Maternal causes

Answer 29

1. The incidence of congenital malformations is 3-4 times higher in the offspring of a diabetic mother. 2. Iodine deficiency in maternal diet leads to baby cretinism. 3. Obese mother gives birth to babies with neurological defects. 4. Pregnant mothers above 40 years old have the higher possibility to give birth to a child suffering from Down syndrome. 5. Mothers with cyanotic heart disease and those living high altitude may give birth to small sized infants with no gross congenital anomalies. 6. Hyperthermia (increased body temperature) either caused secondary to bacterial infections or externally as exposure to hot sun or sauna systems affect neurulation leading to anencephaly or spina bifida.

Question 30

Paternal causes

Answer 30

1. Exposure to chemicals and radiation can cause mutation in male germ cells. 2. Advanced age may lead to chromosomal defects in male gametes with subsequent anomalies in the offspring. Eg. Down syndrome.

Question 31

Chromosomal abnormalities

Answer 31

1. Numerical. 2. Structural.

Question 32

Numerical chromosomal abnormalities

Answer 32

The offspring has abnormal chromosomal number. It could be autosomal or in sex chromosomes. It is divided into: 1. Autosomal. 2. Sex chromosomes.

Question 33

Autosomal

Answer 33

1. Trisomy 21 (Down syndrome or mongolism). 2. Trisomy 13 15 17 18.

Question 34

Trisomy 21 (Down syndrome of mongolism)

Answer 34

Extra chromosome 21 so the chromosomal number is 45 + XX or XY.

Question 35

Trisomy 21 (Down syndrome of mongolism) cause

Answer 35

This occurs due to non disjunction of chromosomes 21 during the 1st meiotic division of the oocyte.

Question 36

Trisomy 21 (Down syndrome of mongolism) percent increase

Answer 36

The possibility of a child with Down syndrome increases with the increase in the age of the mother.

Question 37

Trisomy 21 (Down syndrome of mongolism) features

Answer 37

Specific facial features with mental retardation.

Question 38

Trisomy 13 15 17 18

Answer 38

1. Less common. 2. Infant suffers from many congenital anomalies and usually dies by the age of 2 months.

Question 39

Sex chromosomes

Answer 39

1. Klinefelter syndrome. 2. Turner’s syndrome.

Question 40

Klinefelter syndrome

Answer 40

1. 44 + XXY. 2. Due to non disjunction of X chromosomes during division of oocyte. 3. Male child she suffers from gynecomastia and infertility.

Question 41

Turners syndrome

Answer 41

1. 44 + X0. 2. Due to non disjunction of sex chromosomes during division of either male or female gametes. 3. A female child suffers from webbed neck and infertility due to agenesis of ovaries.

Question 42

Structural chromosomal abnormalities

Answer 42

They result from breaking of a chromosome due to exposure to viruses, radiations, or drugs. Divided into: 1. Cri-du-chat syndrome. 2. Angelman syndrome.

Question 43

Cri-du-chat syndrome

Answer 43

Partial deletion of short arm of C5. Symptoms: 2. Cat like cry. 3. Microcephaly. 3. Mental retardation. 4. Congenital heart disease.

Question 44

Angelman syndrome

Answer 44

Partial deletion of long arm of C15. Symptoms: 1. Mental retardation. 2. Inability to speak. 3. Poor motor development. 4. Prolonged period of laughter.

Question 45

Prevention of birth defects

Answer 45

1. Supplementation of salt or water supplied with iodine: - Mental retardation. - Bone deformities resulting from cretinism. 2. Folate supplementation: - Lowers incidence of neural tube defects: * spina bifida. * anencephaly. - Reduces the risk for hyperthermia-induced abnormalities. 3. Avoidance of alcohol and other drugs.

Question 46

Prenatal diagnosis of fetal malformations

Answer 46

1. Ultrasonography examination. 2. Maternal serum screening (level of alpha fetal-proteins). 3. Amniocentesis (genetic analysis of sloughed fetal cells). 4. Chorionic villus sampling (sample from placenta for genetic analysis).

Question 47

Fetal therapy

Answer 47

1. Fetal transfusion. 2. Fetal medical treatment. 3. Fetal surgery. 4. Stem cell therapy. 5. Gene therapy.

Question 48

Fetal transfusion

Answer 48

1. In case of fetal anemia produced by maternal antibodies. 2. Blood transfusion to the fetus. 3. Ultrasound to guide insertion of needle to umbilical cord vein. 4. Directly into the fetus.

Question 49

Fetal surgery

Answer 49

1. Open fetal surgery. 2. Minimal fetoscopic surgery. 3. Centers with well trained teams and only with no reasonable alternatives. - Repairing congenital diaphragmatic hernia. - Congenital heart diseases. - Neural tube defects.

Question 50

Stem cell therapy

Answer 50

1. Because the fetus doesn’t develop any immunocompetence before the 14th week gestation, it may be possible to transplant tissues or cells before this time without rejection. 2. Hematopoietic stem cells for treatment of immunodeficiency and hematologist diseases.

Question 51

Gene therapy

Answer 51

Experimental technique that uses genes to treat and prevent disease. In the future, this technique may allow managing a disorder by: 1. Replacing mutant gene that causes disease with a healthy copy of the gene. 2. Inactivating a mutated gene that is functioning improperly. 3. Introducing a new gene into the body to help fight a disease.