Everyone, welcome back to parently. It's Dr. Mark Boyd. Today we're going to talk about a very interesting topic that's near and dear to my heart. I know you as a pregnant woman, it's going to be near and dear to your heart as well. Now trying to establish how far along you are is very, very important in understanding the anatomy of the first trimester of your baby. Dramatic life altering events are going to occur in this very first six eight weeks of your baby's life.
Now, as we've discussed in another video conception occurs with oscillation, that means the egg and the sperm getting together this occurs in the fallopian tube. After about seven days, anywhere from three to seven, the fallopian tube is going to release the egg and it's going to come down into the uterus. At that point, the new baby to conceive baby is going to burrow itself into the uterus, at that point, it's called a zygote. As this baby grows and develops its surrounding structure, which is called a placenta, it will become what's called an embryo. And it will remain this term embryo until around your ninth or 10th week, and we changed the name at that point to a fetus. Now what happens during this first part of pregnancy, the conception part, up until the end of your first trimester, what happens anatomically, size wise and then we're going to try to correlate this with ultrasound so that you have an ultrasound.
This will make sense to you. Now in the first four to five weeks of gestational age, the baby forms most of its structures, the brain forms the spinal cord, and column form. The eyes form many of the ligaments form at the end of your fourth week. The baby is The size of an apple seed. So you can imagine how small an apple seed is. And it's just an amazing process.
I call it a miracle that the baby is so complex at this point, again with a heart and a nervous system. Now, if we record light with that with ultrasound, so you are your health care provider, and they do an internal sonogram. What will you see? Well, at this point, at four weeks, you won't see anything in the uterus, you'll see what's called a yolk sac. This is what provides nutrition to the new baby and you'll see an empty gestational sac. Now it's empty not because something's not there, it's empty because we can't see it just because our ultrasounds are not this accurate.
Now, as we fast forward up to eight weeks, your baby's remainder of the organs, excluding a few are going to completely form. So from four weeks gestational age up until eight weeks. Most everything else Just forming. Now if we were to do an ultrasound at this point, at eight week mark, your baby is the size of an olive inside the gestational sac will be the baby in the amniotic fluid. The placenta at this point is almost completely ready to take over the nutritional aspects of the baby. Remember, prior to this, it's been the ovary and the yolk sac.
But around the eight to the 10th week, the placenta will start its process of giving nutrition to the baby. Now, if we fast forward to the 10th week, and then I'm I mentioned the 10th week and the 12th week, the 10th week, all four of the extremities are there, the arms and the legs. And also at this point, the baby's genitalia have completely developed on ultrasound, we can't see this, but whether your baby is a boy from biological standpoint, or a girl from a biological standpoint, these organs will have formed by the 10th week and let's fast forward to The 12th week, the baby looks like a baby at this point, we call it a fetus. So if we were to look at the size of the baby at this point, it's the size of a line. The baby at this point has a head that looks like a normal baby.
It has a body that looks like a normal baby, all for the extremities or their arms and legs. Even though the genitalia is completely formed at the 12 week mark. ultrasound wise we still can't identify whether this is a boy or girl. You need to fast forward to the 16 to 20 week mark before we can see the genitalia life in the first trimester, baby. It's an amazing, amazing process. I hope this was helpful.
Have a great day.