14 Questions
At the beginning of the fetal period, what is the approximate weight of the fetus?
30 gm
At what stage can the sex of the fetus be determined using ultrasound?
End of the third month
When can the mother typically feel the movement of the fetus?
End of the fourth month
What is the length of the fetus at birth?
50 cm
What is the approximate age of a full-term fetus after fertilization?
266 days
What is the proportion of the fetal length constituted by the head at the 3rd month?
1/2
What are the agents that produce congenital anomalies during pregnancy known as?
Teratogens
What is the length of pregnancy for a full-term fetus?
280 days
What is the most sensitive period for teratogenesis?
Embryonic period
What is the characteristic of dizygotic twins in terms of sex and blood group?
They may have the same or different sexes and blood groups
What is the characteristic of monozygotic twins in terms of physical appearance?
They are physically identical
What happens if the separation of the inner cell mass is incomplete in monozygotic twins?
The embryos will share the same amniotic cavity
What is the characteristic of dizygotic twins in terms of placenta and amnion?
They always have separate placentae and amnions
What is the percentage of monozygotic twins?
1/3
Study Notes
Fetal Period
- Characterized by rapid growth and maturation of organs
- Weight of fetus increases from 30 gm to 3 kg at full-term
- Length of fetus at birth is about 50 cm (Crown-heel)
- Sex of fetus can be determined from 12 weeks due to external genitalia appearance (ultrasound)
- Fetus movement can be felt by mother from 16th week
- Fetal heartbeat can be heard through stethoscope from 16th week
- Fetus can live if born after 24 weeks (6 months) of development
Pregnancy Duration
- Full-term pregnancy is 280 days or 40 weeks after last menstrual period
- Age of full-term fetus is 266 days or 38 weeks after fertilization (2 weeks less than pregnancy duration)
Estimation of Embryonic and Fetal Ages
- Can be estimated using ultrasound
- Common measurements: crown-rump length (sitting height), crown-heel length (standing height), head circumference, and biparietal diameter
- Head circumference:
- 1/2 of fetal length at 3rd month
- 1/3 of fetal length at 5th month
- 1/4 of fetal length at birth
Congenital Anomalies
- Many factors can interact with embryonic development, including environmental, genetic, or both
- Teratogens (e.g., drugs, viruses) can cause congenital anomalies
- Most sensitive period for teratogenesis is embryonic period when structures are first formed and differentiated
Twins
-
Dizygotic Twins (2/3):
- Result from fertilization of two ova by different sperms
- Non-identical twins, may have same or different sexes, and different blood groups
- Always have two amnions, two chorions, and two placentae (may fuse)
-
Monozygotic Twins (1/3):
- Result from single fertilized ovum
- Identical twins, same sex, blood group, and physically similar
- Different development stages:
- Separation at two-cell stage: separate chorionic sacs, amniotic cavities, and placentae
- Separation at blastocyst stage: common chorionic sac, common placenta, and two separate amniotic cavities
- Incomplete separation: shared amniotic cavity (rare)
Explore the fetal period, characterized by rapid growth and organ maturation. Learn about fetal weight and length, as well as determining the sex of the fetus.
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