Highlights

  1. The first trimester of pregnancy starts without any signs you’re pregnant, and ends with a body that has adjusted to carrying a child.
  2. Symptoms won’t start until the fourth week — when a woman can expect to miss her period and may experience mild cramping and blood spotting.
  3. Morning sickness may begin around week five or six, but nausea and vomiting can happen any time of the day.

The earliest signs of pregnancy are often easily overlooked. Many women know that a missed period may indicate pregnancy, but so can bloating, spotting, and cramping. Learn when and why symptoms occur in the first weeks of pregnancy.

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Week 1 and 2

Determining the exact time of conception and a woman’s due date is more complicated than you might think. Though it may sound odd, your first week of pregnancy is based on the date of your last menstrual period, which occurred before you became pregnant. Your expected delivery date is calculated using the first day of your last period. For that reason, this week counts toward your 40-week pregnancy.

It isn’t until sometime in week two that ovulation occurs. Ovulation is the release of the most mature egg from the ovary. The mature egg travels from the ovary down a fallopian tube toward the uterus. While the egg is in the tube, a woman can become pregnant if the egg meets a sperm.

Symptoms

Because you’re not yet pregnant in week one, you have no symptoms of pregnancy. You may have symptoms of your menstrual period, however. You will also not feel any symptoms or signs of pregnancy during or immediately after fertilization.

You will also not feel any symptoms or signs of pregnancy during or immediately after fertilization.

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Week 3

The egg and sperm combine to make one cell in a process called fertilization. A baby’s gender is determined at the moment of fertilization. The fertilized egg makes its way toward your uterus. What was once a single cell is now multiplying and dividing into many cells. This process, called cell division and differentiation, creates a blastocyst, a fluid-filled group of cells. This blastocyst develops two layers: an inner cell mass (ICM) and an outer layer of trophoblast cells. By the end of this week, the blastocyst will attach itself to the lining of your uterus, also called the endometrium. This process is called implantation.

Symptoms

This early stage of pregnancy, when the fertilized egg moves to the uterus, often does not produce any detectable signs or symptoms.

Week 4

According to the Mayo Clinic, implantation occurs when the blastocyst burrows into the uterine wall for nourishment. The cells continue to grow and divide. By this stage of your pregnancy, the ICM can be divided into two layers: the epiblast and the hypoblast. These layers of cells will eventually become the baby’s body parts and organs.

In week four, the cluster of cells continues to implant itself into the uterus. The cells of the trophoblast are developing ways to feed the baby throughout the pregnancy. Once implantation is complete, your body will begin producing human chorionic gonadoptropin (hCG). This hormone helps the body maintain the pregnancy. It also tells the ovaries to stop releasing mature eggs each month. You will likely miss your next period.

Symptoms

During the fourth week, you won’t begin your next menstrual period. For many women, the very first detectable sign of a pregnancy is a missed period.

During implantation, some women experience mild cramping and blood spotting. You could mistake the signs and symptoms of implantation as your period. In this case, you may not realize that you’re pregnant.

However, if you were to take a urine pregnancy test at this point, it would likely show that you’re pregnant. In week four, a pregnancy test will be able to detect hCG levels in your urine.

Other symptoms of pregnancy that occur during this week include fatigue, nausea, tingling or aching breasts, frequent urination, and feeling bloated.

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Week 5

In week five, the developing embryonic cells in your uterus begin to take a recognizable shape. According to the Mayo Clinic, week five marks the beginning of the embryonic period. The cells that will eventually become the baby’s spinal cord and brain begin to form.

Symptoms

Fatigue, feelings of being bloated, frequent urination, aching breasts, and mood swings may all begin or continue during week five. You may or may not also be experiencing nausea.

Week 6

In week six, an embryo’s nervous system and brain are rapidly developing. The heart begins pumping blood, and the eyes are developing, too. The embryo also begins to bud arms and legs.

Symptoms

By now, your body is likely giving you all of the signs and symptoms of pregnancy. The most common symptoms hit full force during this sixth week. Morning sickness, for example, may develop. Despite its name, the queasy stomach, nausea, and vomiting associated with morning sickness can occur any time of day. Your breasts may become increasingly tender and achy, and you may find yourself running to the bathroom because you need to urinate more frequently.

Hormones control so many of the symptoms you experience. When you become pregnant, your body’s hormones jump onto a rollercoaster of highs and lows. Mood swings, frequent urination, temperature changes can all be related to these hormone swings.

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Week 7

In week seven, the umbilical cord, which provides the embryo with nutrients and oxygen during the pregnancy, is finished forming. The lungs and digestive system are still developing. Facial features are also becoming more defined.

Symptoms

Your body is ready for the rest of your pregnancy, and it’s trying to protect the growing embryo. To do that, you will develop a mucous plug during this week. This plug protects the uterus by sealing off the opening of the cervical canal.

Week 8

The embryo is continuing to grow and develop more recognizable features, including hands, feet, and eyes. The genitals are still too small and underdeveloped, so you won’t know your baby’s gender for a few more weeks.

Symptoms

A missed period, nausea, vomiting, fatigue (possibly extreme), bloating, and possible weight gain are all cluing you into your pregnancy. If you didn’t know you were pregnant before this week, you will probably begin to wonder.

Your body is working hard to help your growing embryo develop healthfully. Pregnancy places a great demand on your body, in particular your vascular system. During this stage of pregnancy, your heart may begin pumping faster and harder. The extra effort is needed to get enough blood from the heart, through the body, and to your embryo.

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Week 9

All of the embryo’s systems continue to develop and become more distinct. Eyelids are forming from flaps of skin over the eyes. A nose could be seen on an ultrasound. Internal reproductive organs are developing. Muscles have begun to form, too, so the embryo may start making movements. However, you won't be able to feel these for a few more weeks.

Symptoms

Many of the same symptoms as week eight will still be present in week nine. For now, symptoms will continue to grow more noticeable because the hormone and chemical changes caused by pregnancy create a lot of extra work for your body. Don't be surprised if extreme fatigue hits in week nine.

Week 10

Starting in week 10, the embryo is now considered a fetus. Fingers and toes begin to develop from the paddle-like appendages that developed earlier in the pregnancy. All of the fetus’s vital organs are beginning to work together.

Symptoms

Symptoms of pregnancy will still be very similar to recent weeks. Nausea, vomiting, mood swings, fatigue, and achy or tender breasts are all common. At this point, your heart rate will go up, but your blood pressure will likely remain the same of go down. Your doctor will check your blood pressure at your first prenatal visit. If your blood pressure increases, it could be a sign of a complication.

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Week 11

In week 11, the fetus is quickly growing. This puts an even greater demand on your body. All of the blood vessels in the placenta are growing in order to supply the fetus with the nutrients and oxygen it needs to grow.

Symptoms

Hormones continue to cause a variety of changes to your body. Your breasts may begin growing. The areola, the area around the nipple, may change to a darker color and may grow larger. If you’ve had bouts with acne prior to your pregnancy, you may experience breakouts again.

Though you may have gained a few pounds in the earliest weeks of your pregnancy, weight gain becomes more common toward the end of your first trimester. The fetus is growing so rapidly that you need to eat more in order to provide it with the nourishment it needs.

Week 12

This part of your baby’s development focuses on fine-tuning many internal functions. The brain is a main focus, but tiny fingernails and toenails have begun growing, too. The kidneys are functioning, and they are producing urine.

Symptoms

The combination of increased blood volume and higher hormone levels pushes more blood through your vessels. This causes the body’s oil glands to work over time. That, in turn, gives your skin a flushed, glossy appearance. Many people may begin saying you have the “pregnancy glow.”

According to the American Pregnancy Association, many women experience decreased morning sickness in week 12.

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Symptoms Dwindle in the Second Trimester

Many of the body changes and symptoms of pregnancy you experience in the first trimester will begin to fade once you reach the second trimester. For example, morning sickness typically only occurs during the first trimester. Other symptoms, like heartburn, may actually stay the same or get worse. Talk with your doctor about any problematic symptoms. Together, you can find relief and comfort for your pregnancy.