Up to 14 weeks
By 14 weeks after your last period, all of your baby's major organs have formed and his intestines are sealed in his abdominal cavity. He's starting to grow and mature.
Your baby at 14 weeks of pregnancy
Your baby's progress
By the 11th week of pregnancy, your baby is recognizable as a human being, and he's now called a fetus (offspring) rather than an embryo. His head is very large compared to the rest of his body - by 14 weeks it's about one-third of his whole length. His eyes are completely formed, although his eyelids are still developing and remain closed. His face, too, is completely formed. His trunk has straightened out and the first bone tissue and ribs appear. He has nails on his fingers and toes and he may have some hair. The external genital organs are now growing and doctors may be able to tell your baby's sex by ultrasound. His heart is beating between 110 and 160 times per minute and his circulatory system is continuing to develop. He swallows amniotic fluid and excretes it as urine. His sucking reflex is getting established - he purses his lips, turns his head, and wrinkles his forehead. The muscles he'll use after he's born for breathing and swallowing are also being exercised. In fact, by the end of this month your baby will begin to move around vigorously, but you probably won't be able to feel his movements until the fourth month.
While your baby will go on relying on the placenta for his nourishment, oxygen, and the clearance of waste until he is born, he has to have a system of blood-cell formation that will eventually support life outside the womb. Towards the end of this month, the yolk sac becomes superfluous as its task of producing blood cells is taken over by your baby's developing bone marrow, liver, and spleen.
His support system
The placenta is developing very quickly, making sure that there's a rich network of blood vessels to provide your baby with vital nourishment. Now the layers thicken and grow until the chorion and membranes cover the entire inner surface area of the uterus. The umbilical cord is now completely mature and is made up of three intertwined blood vessels wrapped in a fatty sheath. The large vein carries nutrients and oxygen-rich blood to your baby, while the two, smaller, arteries carry waste products and oxygen-poor blood from your baby back to the placenta. The umbilical cord is coiled like a spring because the sheath is longer than the blood vessels. This allows your baby plenty of room to move around without the risk of damaging his lifeline.
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