Organ Development During Pregnancy
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Organ Development During Pregnancy

The development of a baby in utero is truly remarkable. Only a few weeks pass between the time an egg is fertilized and the heart begins to beat. While organ development during pregnancy may be rapid, some organs are not fully functional until the baby is full-term and ready to be born. Others, such as the heart, are functional before the end of the first trimester of pregnancy.

Organ Development During Pregnancy

It only takes three months for most of your baby’s organs to be formed. Some are rudimentary, while others, such as the heart, are in working order. The brain grows rapidly throughout the pregnancy. It takes until the end of the fifth month of pregnancy for most of the internal organs to be fully functional, although they will continue to mature until the baby is full-term. This does not include the kidneys and lungs, which are the most fragile. The kidneys are not fully developed until the end of the eighth month, according to Sutter Health, and the lungs are not fully developed until the baby is full-term.


Size does not matter when it comes to the development of your baby’s organs. At the end of your fourth week of pregnancy, your baby is only 1/4 inch long, according to Sutter Health. Still, the heart, digestive system and spine are beginning to form in the embryo’s microscopic body. When the baby is eight weeks old, it is only 1 inch long and yet, the heart is functioning and the reproductive organs are forming. By the end of the third month of pregnancy, although the baby is only around 2 to 3 inches long, most of the organs are developed.


Ultrasounds are used to identify the organs of a baby. Many parents are especially interested in the heart and reproductive organs. A beating heart can be seen on an ultrasound as early as the sixth or seventh week of pregnancy. A Doppler can be used to hear the heart as early as the ninth or 10th week of pregnancy. Male and female reproductive organs look remarkably similar as they develop up until the 18th or 19th week of pregnancy, when the differences between the two are finally noticeable. Many women choose to have an ultrasound at this time to determine the sex of their baby.


Lung development is watched carefully when there is a danger of a premature birth. The biggest issue with premature babies is often the fact that their lungs are underdeveloped, according to the American Pregnancy Association. A baby’s lungs need time to develop surfactant, which prevents the lungs from collapsing. For this reason, babies born prematurely may struggle to breathe and may have to be placed on a ventilator, which can damage the lungs even further. Other complications may include pneumonia.


Drug use and other poor health practices can have a dramatically negative effect on the development of a fetus, and especially in the organ development during pregnancy. This is especially true during the early weeks of a pregnancy, when the baby is growing and changing so rapidly. It is important to refrain from smoking, taking drugs or drinking alcohol throughout the course of your pregnancy.

Organ Development During Pregnancy

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