30 Questions
What is the role of human chorionic gonadotropin (HCG) in early pregnancy?
Maintaining the corpus luteum of the ovary
What is the basis for early pregnancy tests?
Detection of human chorionic gonadotropin (HCG) in maternal blood
In IVF, how is fertilization typically achieved when sperm count is normal?
Placing a droplet of sperm on each egg
At what stage are embryos typically placed into the uterus during IVF procedures?
Blastocyst stage
What is Preimplantation Genetic Diagnosis (PGD) used for in the context of IVF?
Screening embryos for genetic disorders
What is the characteristic of cells in the early embryo up to the 8-cell stage?
Totipotent
What is the duration of human pregnancy based on fertilisation?
266±3 days or 38 weeks
When does implantation typically occur in human embryonic development?
7 days after fertilisation
What is the most common ectopic implantation site for embryos?
Ampulla of the uterine tube
Which structure gives rise to the future placenta in human embryonic development?
Trophoblast
At what stage does a fertilised egg have two nuclei, one from the egg and one from the sperm?
Zygote
How many cells are present in a three-day-old embryo?
107
What is the main source of human embryonic stem cells?
Inner cell mass
Which type of twins are derived from 2 eggs?
Fraternal twins
At what stage do 35% of monozygotic twins divide to get two babies with two amnions?
Between 2-8 cell stage
What has greatly increased the number of fraternal (dizygotic) twins?
IVF procedures
What is the rate of twins in the USA as mentioned in the text?
3%
What type of cells can embryonic stem cells be induced to become under certain experimental conditions?
Muscle cells
What is the recommended daily intake of folate for women of childbearing age to reduce the risk of neural tube defects?
0.4 mg
Which antiepileptic medication is associated with an increased risk of spina bifida if used during early pregnancy?
Carbamazepine
During which period does organ system development occur in a human embryo?
Weeks 5-8
At what stage is the embryo still to complete the development of the palate and external genitalia?
44-day embryo
What occurs during the fetal period between weeks 9-38 of pregnancy?
Massive neuronal cell formation for the cerebral cortex
When is chorionic villous sampling usually performed?
8-10 weeks gestation
What is the significance of gastrulation in human embryonic development?
Conversion of the bilaminar disc into three layers
What was the impact of reducing the number of embryos transferred during IVF from 3 to 2 in the early 1990s?
Decreased rate of multiple births
Which statement about monozygotic twins is accurate according to the text?
Separation at the two blastomere stage leads to twinning
What is established around 21 days gestation in human embryonic development?
Circulation
At what stage does human implantation typically occur?
9-10 days
What is the most common cause of identical twins?
Splitting of the inner cell mass
Study Notes
Early Pregnancy and Fertilization
- Human chorionic gonadotropin (HCG) is produced by the trophoblast and maintains the corpus luteum of the ovary, which in turn produces progesterone, essential for early pregnancy.
- HCG can be detected in maternal blood and forms the basis of early pregnancy tests; detection in urine is less sensitive.
In Vitro Fertilization (IVF)
- In IVF, one or more eggs (oocytes) are fertilized outside the body, either by placing a droplet of washed sperm onto each egg or through intra-cytoplasmic sperm injection (ICSI) if the sperm count is low.
- Fertilized eggs (zygotes) can be cultured for 3-6 days before being placed into the uterus, allowing for the selection of healthy blastocyst stage embryos.
Preimplantation Genetic Diagnosis
- Cells from the early embryo (until about the 8-cell stage) are totipotent, capable of forming a complete human, and can be used for genetic screening.
- Over 100 diseases can be detected, including hemophilia A, muscular dystrophy, Tay-Sachs disease, cystic fibrosis, and Down syndrome.
Stem Cell Research
- Stem cells are unspecialized cells that can renew themselves for long periods through cell division and can be induced to become cells with special functions.
- Human embryonic stem cells are obtained from the inner cell mass of the early embryo.
Multiple Gestations (Twins)
- About 1 in 80 human births (0.8%) is a twin pregnancy, with about 2/3 being fraternal (dizygotic) and 1/3 being identical (monozygotic).
- IVF has increased the number of fraternal twins, with the rate of twins in the USA being 3% in 2001.
- In Sweden, the twin rate increased from 0.9% in 1982 to 1.7% due to IVF.
Implantation and Embryonic Development
- Human implantation occurs about 7 days after fertilization, where the developing embryo must pass through the uterine epithelium.
- The first week of human embryonic development is critical, with gastrulation converting the bilaminar disc into three layers.
- Human pregnancy lasts about 266±3 days or 38 weeks, with obstetricians timing pregnancy from the last day of the menstrual period.
Ectopic Pregnancies and Folate
- Implantation in a nonuterine site occurs at a rate of about 0.25-1%, with the ampulla of the uterine tube being the most common ectopic implantation site.
- Folate consumption (0.4 mg daily) is recommended for all women of childbearing age to reduce the risk of neural tube defects.
This quiz covers the key events in human embryonic development from fertilisation to implantation during the first four weeks. It includes concepts such as embryonic age, pregnancy duration, and the stages of early embryo formation.
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