Fetal development in the first 3 months

This is an automatically translated article.

The article is professionally consulted by Specialist Doctor II Bui Minh Phuc - Department of Obstetrics and Gynecology - Vinmec Ha Long International Hospital.
Immediately after the egg is fertilized by the sperm, a complex but predictable process takes place to form a baby. Although it is the first 3 months, the fetus will still have certain developments.

1. Weeks 1 and 2: Prepare

There is no pregnancy in the first or second week of pregnancy.
Insemination usually takes place two weeks after the start of the last menstrual period. By convention, the due date is calculated 40 weeks after the first day of the last menstrual period, which means that the duration of the period is also included in the time of pregnancy, despite the fact that fertilization has not yet occurred. happen.

2. Week 3: Conceive

After the egg is fertilized by the sperm, it becomes a zygote in the fallopian tube. If only one fertilized egg will form only one zygote, if more than one egg matures and is fertilized or the fertilized egg splits in two, there will be more than one zygote.
The zygote has a genetic composition of 46 chromosomes, of which 23 are inherited from the father and 23 are inherited from the mother. These chromosomes determine the sex of the child, as well as the biological and physical characteristics of the child.
Immediately after being fertilized, the zygote will gradually move along the fallopian tube to enter the uterine cavity, and in the meantime, it also divides to form the morula embryo.

3. Week 4: Nesting

The blastocyst divides rapidly and begins to penetrate the lining of the uterus for implantation.
Inside the embryo sac, the inner cell group develops into the embryo, while the outer layer of cells forms the placenta - the part responsible for nurturing the fetus during pregnancy.

4. Week 5: Hormone levels increase

During the 5th week of pregnancy (equivalent to the 3rd week after fertilization), the level of the hormone HCG (produced from the embryo sac) increases rapidly. The rise in HCG is a signal for the ovaries to stop releasing eggs and secrete more of the hormones estrogen and progesterone. Increased levels of the hormones estrogen and progesterone stop the menstrual cycle (a classic sign of pregnancy), and stimulate the growth of the placenta.
The embryo now has three layers. The ectoderm will develop into the baby's skin, central and peripheral nervous system, eyes and inner ear. The dermis will form the baby's heart and circulatory system, bones, ligaments, kidneys, and most of the reproductive system. The endoderm will form the lungs and digestive tract.

5. Week 6: Neural tube closes

The fetus is growing rapidly this week. Just four weeks after fertilization, the neural tube at the back of the fetus begins to close. The fetal brain and spinal cord develop from the neural tube. The heart and other internal organs also begin to take shape.
The structures necessary for the development of the eyes and ears also develop. Small buds appear that will later become the baby's arms. The fetal body begins to take a curved shape like the letter C.

6. Week 7: The fetal head develops

Week 7 of pregnancy (equivalent to 5 weeks after fertilization), the brain and face of the fetus develop and grow. The dimples that would later become the baby's nostrils were already visible. The retina gradually begins to form.
The shoots that later become the lower limbs appear. The arm buds that appeared last week are now shaped like paddles.

7. Week 8: The baby's nose is forming

In the 8th week of pregnancy (equivalent to 6 weeks after fertilization), the lower extremity buds have taken the shape of a paddle. Fingers begin to form. The parts that later became the ears and eyes were clearly visible. The upper lip and nose have formed. Neck and torso begin to straighten.
By the end of the 8th week, the fetus is about 16 mm long.

8. Week 9: Fetal toes appear

At the 9th week of pregnancy (equivalent to 7 weeks after fertilization), fetal arms develop and elbows appear. Toes were visible and eyelids formed. The fetal head is quite large, but the chin part of the fetus is still incomplete.
By the end of the 9th week, the fetus is about 23 mm long.

9. 10th week: Fetal elbow flexes

By the 10th week of pregnancy (equivalent to 8 weeks after fertilization), the fetal head becomes rounder.
By this time, the fetus is able to bend the elbow. The toes and fingers are no longer webbed and become longer. The eyelids and outer ears continue to develop. The umbilical cord is clearly visible.

10. Week 11: Fetal genitals develop

At the beginning of the 11th week of pregnancy (equivalent to the 9th week after fertilization), the fetal head is about half the length of the total fetal length, however the fetal body begins to develop rapidly.
The new baby is officially described by the word “pregnant”. The baby's face is wide, the eyes are far apart, the eyelids are closed. The future tooth germ appears. Red blood cells begin to form in the fetal liver. By the end of the 11th week, the external genitalia begin to develop (to become a penis for a male fetus, or a clitoris and large labia for a female fetus).
Fetal length is now about 41 mm and weighs about 8 g.

11. Week 12: nails form

In the 12th week of pregnancy (equivalent to the 10th week after conception), the baby's fingernails gradually appear. The baby's face is also more developed, looks clearer. The intestinal system is also more developed in the womb. The fetus begins to move on its own.
By this time the fetus is about 54 mm long and weighs about 14 g. The first 12 weeks is the most sensitive time during pregnancy, the health of both mother and baby is very vulnerable, especially pregnant women with a history of miscarriage should be closely monitored because of the risk of second miscarriage. 2 is very high. In order for mother and baby to be healthy, pregnant women need to pay attention to important issues such as:
Understanding early signs of pregnancy, pregnancy poisoning, bleeding during pregnancy. Timely, correct and sufficient first prenatal check-up, avoiding too early/too late. Fetal malformation screening at 12 weeks detects dangerous fetal malformations that can be intervened early. Distinguish between normal vaginal bleeding and pathological vaginal bleeding for timely intervention to maintain pregnancy. Screening for thyroid disease in the first 3 months of pregnancy avoids dangerous risks before and during delivery. Vinmec currently has many maternity packages (12-27-36 weeks), in which the 12-week maternity package helps monitor the health of mother and baby right from the beginning of pregnancy, early detection and timely intervention of health issues. In addition to the usual services, the maternity monitoring program from 12 weeks has special services that other maternity packages do not have such as: Double Test or Triple Test to screen for fetal malformations; Quantitative angiogenesis factor test to diagnose preeclampsia; thyroid screening test; Rubella test; Testing for parasites transmitted from mother to child seriously affects the baby's brain and physical development after birth. When the body shows abnormal signs, pregnant women should see a specialist soon for examination and treatment advice.

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