By: Farida Husseini
Intro to Development -- Conception:
Women experience a monthly reproductive cycle in which they will either become pregnant, or have their menstrual period. This cycle happens during the time one starts their reproductive years; usually during an ndividual’s teen years until they reach menopause around the age of 50.
During a reproductive cycle in which one gets pregnant, there are several steps that a fertilized egg goes through to become a sperm, a fetus, and eventually, a baby:
First, a group of eggs (called oocytes) get ready to leave the ovary for ovulation (release of the egg).
Then these groups of eggs develop in small, fluid-filled cysts called follicles. Out of this group, one egg will become mature and continue on with the cycle.
This follicle then suppresses all the other follicles in the group, preventing them from growing any further.
At this point the mature follicle opens and releases the egg from the ovary. This step is called ovulation.
After ovulation the opened/ruptured follicle develops into a structure called the corpus luteum (CL); the CL forms from cells of the ovarian follicle wall during ovulation. The purpose of the CL is that it secretes progesterone and estrogen. The progesterone helps prepare the endometrium (lining of the uterus). This is the place where a fertilized egg settles to develop.
**If an individual does not get pregnant during their monthly cycle, the lining of the uterus is what is shed during their period.
Intro to Development -- After Conception:
Within the twenty-four hours after fertilization, the egg begins rapidly dividing into many cells.
The egg remains in the fallopian tube for about three days after conception.
The fertilized egg (blastocyst) continues to divide as it passes slowly through the fallopian tube to the uterus.
Then, the egg attaches to the endometrium. This process is called implantation.
Stages of Growth Month-by-Month in Pregnancy:
First trimester: Conception to twelve weeks. During the first trimester, the baby will develop from a small group of cells into a fetus that is starting to have a baby’s features.
Month 1: Weeks 1-4. The fertilized egg grows, and the placenta develops. The placenta is a round, flat organ that transfers nutrients from the mother to the baby, and transfers wastes from the baby. Circulation begins as the tiny"heart" tube will beat 65 times a minute by the end of the fourth week. By the end of the first month, the baby is about 1/4 inch long.
Month 2: Weeks 5-8. During this time period, the baby’s facial features continue to develop. The neural tube (brain, spinal cord and other neural tissue of the central nervous system) is well formed now. In addition, bone starts to replace cartilage tissue. At this point, the baby’s head is the same size as the rest of its body. At around 6 weeks an actual heartbeat can be detected, and the baby is referred to as a fetus instead of an embryo. By the end of the second month the heartbeat can be detected, and the baby is referred to as a fetus instead of an embryo. By the end of the second month the baby is about an inch long.
Month 3: Weeks 9-12. During weeks 9-12 the baby's arms, hands, fingers, feet and toes are fully formed. By the end of the third month, the baby is fully formed -- from this point on, it will just be growing in size. In addition, by the end of month 3 the baby is about 4 inches long and weighs about 1 ounce.
Second trimester: From weeks 13-26. During the second trimester, the baby will start to develop facial features. The sex of the baby can also be determined during this period -- this is typically done through an anatomy scan.
Month 4: Weeks 13-16. During this time period, the baby’s heartbeat can be heard through an instrument called a doppler. Many of the features are well defined, and the nervous system is starting to function. By the end of the fourth month the baby is about 6 inches long and weighs about 4 ounces.
Month 5: Weeks 17-20. The baby’s movements can be felt as the baby is developing muscles and exercising them. Hair begins to grow on the baby’s head and the baby’s skin is covered with a white coating called vernix caseosa. Vernix caseosa is a substance that is used to protect the baby's skin from long exposure to amniotic fluid -- it is shed right before birth. By the end of the fifth month the baby is about 10 inches long.
Month 6: Weeks 21-24. During this time, both footprints and fingerprints are available and the eyelids begin to part and the eyes open. The baby’s skin is red in colour, and veins are visible through its translucent skin. If born prematurely the baby can survive after week 23 in the ICU (Intensive Care Unit). By the end of the sixth month, the baby is about 12 inches long.
Month 7: Weeks 25-28. The baby continues to mature/develop and their hearing is fully developed. The baby also responds to stimuli. By the end of the seventh month, the baby is about 14 inches long.
Third trimester: From week 27 to the end of pregnancy. This is the final part of pregnancy. During this trimester, the baby will continue gaining weight.
Month 8: Weeks 29-32. During this time period the baby will continue to mature and develop reserves of body fat. It will also kick more often as most of the internal systems are well developed.
Month 9: Weeks 33-36. During this time period the baby will continue to grow and mature. The lungs are almost fully developed, and the baby’s reflexes are coordinated. At this point, the baby is about 17 to 19 inches long.
Month 10: Weeks 37-40. One can go into labour at any time during this time period. The baby’s movements are also less frequent due to there being tight space. The baby’s position will move towards the uterus (their head moves nearer to the pelvis) to prepare for birth -- this happens right before labour! At this point the baby is about 18 to 20 inches long and weighs about 7 pounds.
References
Cleveland Clinic. 2021. Fetal development: Month-By-Month Stages of Pregnancy. [online] Available at:
<https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth#:~:text=Fetal%20Development%3A%20Stages%20of%20Growth,weeks%20to%20a%20typical%20pre gnancy.> [Accessed 12 April 2021].
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