Here are the stages of development of the fetus during the first
trimester of pregnancy:
Weeks 1 & 2
This is when ovulation has occurred. Once conception takes place, a zygote is created from the fusion of the sperm and ovule. The fertilized egg needs a couple days in order to travel down through the fallopian tube (the tube that connects the ovary to the uterus) toward the uterus (womb), dividing into cells; it is called a morula. The morula then becomes a blastocyst and will eventually end up in the uterus. In the period between 6-12 days after conception, the blastocyst will implant into the lining of the uterus and begin the embryonic stage.
Week 3 – Gestational Age (Fetal Development – Week 1)
The embryo is undergoing development of the brain, spinal cord, heart, and gastrointestinal tract.
Week 4 & 5 – Gestational Age (Fetal Development – Weeks 2 & 3)
Arm and leg buds may be visible but not clearly discerned. The heart is now beating at a regular rhythm. The placenta has begun to form and is producing some important hormones. The rudimentary structures that will transform into the eyes and ears are appearing. The embryo is about 0.5 cm long by the end of these weeks.
Week 6 – Gestational Age (Fetal Development – Week 4)
The lungs, jaw, nose, and palate begin to form. The hand and feet buds, which are the early structures that will later become the actual hands and feet, have webbed structures. The brain continues to develop. During a vaginal ultrasound examination, the doctor may hear an audible heartbeat at this time. The embryo is about 0.75 cm in length.
Week 7 – Gestational Age (Fetal Development – Week 5)
At seven weeks of gestation, every essential organ has begun to form, but the overall weight of the embryo is still very small. The hair and nipple follicles are forming, and the eyelids and tongue have begun formation. The elbows and toes are more visible as the trunk begins to straighten out.
Week 8 – Gestational Age (Fetal Development – Week 6)
The ears are continuing to form externally and internally. Everything that is present in an adult human is now present in the small embryo. The bones are beginning to form, and the muscles can contract. The facial features continue to mature, and the eyelids are now more developed. The embryo is about 2.5 cm long.
Weeks 9 through 13 – Gestational Age (Fetal Development – Weeks 7 through 11)
Ten weeks of gestation marks the end of the embryonic period and begins the fetal period. The fetus is about 7.5 cm in length and weighs about 28 grams. The genital organs have clearly formed, but it is still not possible to identify the sex of the baby on an ultrasound. The eyelids close and will remain closed until the 28th week of gestation. The fetus can make a fist, and the buds for baby teeth appear. The head is nearly half the size of the entire fetus.
trimester of pregnancy:
Weeks 1 & 2
This is when ovulation has occurred. Once conception takes place, a zygote is created from the fusion of the sperm and ovule. The fertilized egg needs a couple days in order to travel down through the fallopian tube (the tube that connects the ovary to the uterus) toward the uterus (womb), dividing into cells; it is called a morula. The morula then becomes a blastocyst and will eventually end up in the uterus. In the period between 6-12 days after conception, the blastocyst will implant into the lining of the uterus and begin the embryonic stage.
Week 3 – Gestational Age (Fetal Development – Week 1)
The embryo is undergoing development of the brain, spinal cord, heart, and gastrointestinal tract.
Week 4 & 5 – Gestational Age (Fetal Development – Weeks 2 & 3)
Arm and leg buds may be visible but not clearly discerned. The heart is now beating at a regular rhythm. The placenta has begun to form and is producing some important hormones. The rudimentary structures that will transform into the eyes and ears are appearing. The embryo is about 0.5 cm long by the end of these weeks.
Week 6 – Gestational Age (Fetal Development – Week 4)
The lungs, jaw, nose, and palate begin to form. The hand and feet buds, which are the early structures that will later become the actual hands and feet, have webbed structures. The brain continues to develop. During a vaginal ultrasound examination, the doctor may hear an audible heartbeat at this time. The embryo is about 0.75 cm in length.
Week 7 – Gestational Age (Fetal Development – Week 5)
At seven weeks of gestation, every essential organ has begun to form, but the overall weight of the embryo is still very small. The hair and nipple follicles are forming, and the eyelids and tongue have begun formation. The elbows and toes are more visible as the trunk begins to straighten out.
Week 8 – Gestational Age (Fetal Development – Week 6)
The ears are continuing to form externally and internally. Everything that is present in an adult human is now present in the small embryo. The bones are beginning to form, and the muscles can contract. The facial features continue to mature, and the eyelids are now more developed. The embryo is about 2.5 cm long.
Weeks 9 through 13 – Gestational Age (Fetal Development – Weeks 7 through 11)
Ten weeks of gestation marks the end of the embryonic period and begins the fetal period. The fetus is about 7.5 cm in length and weighs about 28 grams. The genital organs have clearly formed, but it is still not possible to identify the sex of the baby on an ultrasound. The eyelids close and will remain closed until the 28th week of gestation. The fetus can make a fist, and the buds for baby teeth appear. The head is nearly half the size of the entire fetus.
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