First trimester of pregnancy
1 and 2 weeks - gestational age
Your period has just ended and
your body is getting ready to ovulate. Most women ovulate about 11 to 21 days
after the first day of their last period. During intercourse, hundreds of
millions of spermatozoa are released into the vagina. The sperm will pass
through the cervix and into the fallopian tube.
If conception occurs, the
sperm enters the egg and creates a unique set of 46 chromosomes called a
zygote, which is the basis of a new human being. A fertilized egg travels for
several days through the fallopian tube to the uterus, dividing into cells;
this is called morula. The morula develops into a blastocyst and ends up in the
uterus. From 6 to 12 days after conception, the blastocyst is introduced into
the uterine mucosa and enters the embryonic stage.
Week 3 - Gestational Age (Fetal Development - Week 1)
The embryo currently undergoes
significant basal growth with the onset of development of the brain, spinal
cord, heart, and gastrointestinal tract.
Weeks 4 and 5 - Gestational Age (Fetal Development - Weeks 2 and 3)
The rudiments of the arms and
legs are visible, but indistinctly distinguishable. The heart is now beating
normally. The placenta has begun to form and is producing some important
hormones, including hCG. The movement of blood through the main vessels is
rudimentary. The first structures are formed that will become the eyes and
ears. At the end of these weeks, the length of the embryo is 0.63 cm.
6 weeks - Gestational Age (Fetal Development - 4 weeks)
Now the formation of the
lungs, jaw, nose and palate begins. The rudiments of the hands and feet have
webbed structures that will become the fingers and toes. The brain continues to
form in its complex parts. A vaginal ultrasound may eventually detect an
audible heartbeat at this time. The embryo is about 1.27 cm long.
Week 7 - Gestational Age (Fetal Development - Week 5)
At the 7th week of pregnancy,
all the main organs have already begun to form in the small body of the embryo,
although it still weighs less than aspirin. Hair follicles and nipples are
forming, eyelids and tongue have begun to form. Elbows and toes become more
prominent as the torso begins to straighten.
8 weeks - Gestational Age (Fetal Development - 6 weeks)
The ears continue to form
outside and inside. Everything that an adult has, now a small embryo also has.
Bones begin to form and muscles can contract. The facial features continue to
mature and the eyelids are now more developed. The embryo is about 2.54 cm long
and the size of a bean.
Weeks 9 to 13 - Gestational Age (Fetal Development - Weeks 7 to 11)
At 10 weeks, the embryo is at the end of the embryonic period and the fetal period begins. The fruit has reached about 7.62 cm in length and weighs about 28 grams. The genital organs are clearly formed as either male or female, but still cannot be clearly seen on ultrasound. The eyelids close and do not open until the 28th week of pregnancy. The fetus can clench its fists and the rudiments of milk teeth appear. The head is almost half the size of the entire fetus.