The First Trimester in Pregnancy: Week by Week Development

Updated on April 20, 2016
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Pregnancy Symptoms

A question I hear/read almost daily is "Am I Pregnant?" Well truthfully no one online or even standing in front of you can actually tell you if you are, in fact, pregnant. Even with a detailed list of pregnancy symptoms you are experiencing the only ones who are going to have an answer are; a pregnancy urine test, blood test or an ultrasound.

That being said, I have included a list of some of the most common early pregnancy symptoms women experience. This will NOT tell you whether or not you are actually pregnant. But will give you an idea if there is a chance that you might be.

Common Pregnancy Symptoms

Whether this is your first pregnancy or not. These are common symptoms, however, there is no way to tell if you will experience all or none.

  • Fatigue- the first trimester can be extremely draining.
  • Nausea and/or vomiting- the sudden change in hormones can send your stomach for a whirl. This does not have to be in the morning. The term "morning sickness" is quite misleading. I personally experienced more of an "evening sickness".
  • Missed period- this is a big one. However, there are reasons other than pregnancy that can lead to a missed period.
  • Frequent urination- as the uterus grows there is an increasing pressure being placed on your bladder. Causing you to pee more often.
  • Sore breasts- this is a very common symptom women may experience. This was the only very early symptom I experienced which lead to taking a pregnancy test.
  • Bloating- if you don't know whether or not you are pregnant yet. Odds are you aren't showing it's bloating.
  • Implantation bleeding- or in other words very light spotting that only lasts a day or two. This usually happens around the seventh day after intercourse.
  • Backache- progesterone prepares your body by loosening everything up so that your uterus can grow. This can cause back aches in early pregnancy.

You may experience all of these symptoms or just one or two of them. Every one of these symptoms could also mean something other than pregnancy is going on with your body. So please, take a test.

Your Pregnancy Development in The First Trimester

Your Pregnancy Week by Week

Week One

Nothing too exciting here. As conception hasn't even happened yet. Instead week one starts on the first day of your menstrual period.

Week Two

Now that your menstrual period is over your uterus begins to a grow a new lining. This lining will be your babies home for the next nine months! Ovulation will likely happen near the end of this week.

Week Three

You egg has been fertilized! And is now undergoing cell division. Near the end of this week (it takes anywhere from 4-7 days to reach your uterus) your fertilized egg will implant into your uterine lining. This may or may not cause some implantation bleeding. Although, you may not even know that you are pregnant your babies gender has already been determined by this point.

Week 4

Congrats your fertilized egg is now considered an embryo! During this week your fertilized egg is separating into a baby and a placenta. A pregnancy test may show up positive at this point. And the early pregnancy symptoms might be setting in. If you have no symptoms don't worry this does not mean you are not pregnant. Your expected period will not appear this week.

Week 5

Your baby is no longer just a ball of cells this week. But is in the beginning stages of looking more like that newborn you have been dreaming about. By this point you have missed your period and have likely either taken a pregnancy test or have been thinking about picking one up.The placenta is now in place. Your babies heart may also begin to beat this week as the circulatory system is the first one to develop.However, you will not be able to hear it quite yet.

Week 6

If your babies heart hadn't begun beating last week it will start to do so this week. And might even been seen on an ultrasound.Your babies brain and neurological system begins to develop quite quickly to keep up with circulatory system. The digestive and respiratory systems also kick into gear this week and begin to develop. Your baby is now approximately 2-5 millimeters. Unfortunately your morning sickness may be at an all time high by this point. Limb buds also appear this week!

Week 7

Your babies respiratory and digestive systems are still busy forming. But the umbilical cord is now formed! Your baby has been busy growing and is now 7-9 millimeters. Approximately the size of a grain of rice. Your mucus plug has formed sealing your cervix closed.

Week 8

Your babies toes and fingers are now beginning to form. And your baby is 8-11 millimeters! You're babies genitals are also beginning to form. However, not enough to determine the sex of your little one. Your babies facial features are also starting to look more human like by this point. And teeth may begin to form under your babies gums. Although you are probably not showing yet you may have noticed some swelling in your abdomen. After all your uterus is now the size of an orange. If you have not already you should make your first prenatal appointment.

Week 9

Your 16-18 millimeter,1 gram babies bones have now begun to form. And he or she now has elbows! Your baby is developing so quickly he/she has even started developing eyelids by this point. Your baby may even start moving around this month. Unfortunately you won't be able to feel these movements quite yet. But you may be able to see them on an ultrasound.

Week 10

Your baby is looking less like a space creature and more like a human this week. His/her fingers are beginning to un-web and the tail is beginning to disappear. All of your babies organs have now been created are beginning to function as a whole. Your baby is now 27-25 millimeters long and approximately 4 whole grams! Your babies heart is likely beating around 160 beats per minute at this point. Most of your babies joints have also formed by now.

Week 11

Congrats! Your baby is now a fetus. Your baby is now about 2 inches long and 7 grams. His or her fingernails have now begun to develop. If you have an ultrasound around this time you will notice that your babies head is much larger than his or her body. Your uterus is now approximately the size of a grapefruit and the placenta may begin to function this week. Your babies irises begin to form this week and his or her eyelids will fuse together reopening later in pregnancy. His or her ears are also moving into the correct position.

Week 12

This is the last week of your first trimester. Luckily you may begin to feel a little better by this point. And the risk of a miscarriage drops significantly after this week. Your baby is now approximately 3.5 inches long and 14 grams. Your placenta has now taken over and is producing all of the necessary hormones. Your babies kidneys are now working too and he or she can now pee. Your baby will swallow amniotic fluid which then comes out as urine. Your babies digestive tract is also practicing necessary movements. Luckily this week your uterus is beginning to move upward and relieving some of the pressure on your bladder. Unfortunately as your uterus continue to grow your frequent bathroom trips will return. Probably one of most exciting events happens this week. You may be able to hear your babies heart beat with a doppler!

Congrats! You have now completed your first trimester and are now headed into the second. The second trimester is often called the "honeymoon trimester". As the fear of miscarriage subsides, nausea may disappear, you may feel less tired and your belly is still small enough to handle.

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.


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