Fetal Development and Growth


Your baby goes through a lot of changes over the course of her nine months inside your uterus. Here is a brief look at just some of the fetal development changes that occur over those many months. Click on the links in each headng to see color photos of how the baby grows and develops.

1st trimester FIRST TRIMESTER
Incredible Color Photos of Fetal Development
Time Stage of Development
Week 2 Although this is considered to be the second week of your pregnancy, you are not actually 2 weeks pregnant yet. During this week, your body will release an egg. As it travels down the fallopian tube, it will be met by your partner’s sperm and fertilization will take place. The fertilized egg, now known as a zygote, will then continue traveling down the fallopian tubes finally reaching the uterus three to four days after fertilization.
Week 4 By the time you are four weeks pregnant, the fertilized egg will have implanted itself into your uterine lining. At this point, the zygote is now known as an embryo. After implantation, the embryo begins to divide itself into two: one part of it will develop into the placenta while the other will go on to become your baby.
Week 6 During the sixth week of your pregnancy, your baby’s heart will begin to beat and blood will start to circulate throughout his body. His umbilical cord will also start to form, as will his head, eyes, intestines and liver.
Week 10 This week marks the end of the embryonic stage of development. For the rest of your pregnancy, your baby will be known as a fetus. Your baby’s external genitalia begin to form this week while her facial features as well as limbs become more apparent. By the end of the week, your baby’s vital organs will not only be formed but will also have begun to work.
2nd trimester SECOND TRIMESTER
Incredible Color Photos of Fetal Development
Time Stage of Development
Week 14 Now that you are 14 weeks pregnant, you have officially started your second trimester. The risk of miscarriage is significantly decreased at this point. In addition to your baby’s reproductive organs developing, your baby will also begin to grow some hair as well as form eyelids, fingernails and toenails. You may even be able to feel your baby moving inside of you this week.
Week 18 By the time your are 18 weeks pregnant, your baby’s finger and toe pads will have formed, which means the fingerprints won’t be far behind. The bones in your baby’s inner ear will have developed enough by this point that he may start responding to loud outside sounds. Additionally, your baby could weigh as much as 7 ounces now and measure about five inches long.
Week 22 Your baby’s sense are so developed by the time you are 22 weeks pregnant that she is likely to starting experimenting. Don’t be surprised to if you see her sucking her thumb on an ultrasound. Your baby’s sweat glands also begin to develop this week while her brain begins to quicken its development.
3rd trimester THIRD TRIMESTER
Incredible Color Photos of Fetal Development
Time Stage of Development
Week 26 During this week, development of the retinas will finish and your baby’s eyes will begin to open and even blink. If your baby were born now, he would have a 50% chance of survival with proper medical care. This week also marks the end of your second trimester. Next week, when you are 27 weeks pregnant, you will officially be in your third (and final) trimester.
Week 30 As your baby begins practicing how to breathe this week, she may end up with a case of the hiccups if she swallows too much amniotic fluid. Your baby is also putting on more body fat, which will help keep her warm when she is born. Although your baby would be premature if she was born now, she would have a good chance of surviving.
Week 40 This is the official end of the gestational period. Even though your baby is ready and able to live outside of you, it is perfectly normal for your baby to arrive as much as two weeks after his due date.

Weeks of Pregnancy

The typical pregnancy is said to last 40 weeks. Yet, for the first two of these weeks, you’re not actually pregnant. Not surprisingly, this method of counting confuses many women. The reason for the addition of two extra, “non-pregnant” weeks is because there is often no sure way to know exactly when conception took place. Therefore, your pregnancy starts on the first day of your last menstrual period.

Not everyone determines a developing embryo or fetus’ age in this way, though. Embryologists often age the child according to when conception is thought to have taken place. To figure out the age of your unborn baby, simply subtract two weeks from your current week of pregnancy.

development of the hands and feet
Photo on Right: Arms and hands develop earlier than legs and feet, but by two months, the lines of palms and footprints are already engraved in the skin.
[Movie Camera]

Watch How The
Unborn Child Grows!

Source: University of Pennsylvania
Basic Embryology Review Program

Note: This is a 3 MB QuickTime movie.

Go to 1st Trimester

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[ heart ]
Listen to the Heartbeat
at only 8 weeks!

Fetal photo credits.

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