Pregnancy by Week: First Trimester (Weeks 1-12)

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Baby's Growth & Development

Near the end of the first trimester (13 weeks gestation) your baby is about three inches long. It weighs about one ounce. The brain and spinal cord are developing rapidly. Your baby can squint, frown, open and shut its mouth, turn its head, make a fist, and kick.

The placenta has formed and blood is now circulating through the umbilical cord. Amniotic fluid cushions the baby and allows the baby to move around easily. At this time, you cannot feel these movements.

The baby's heartbeat may be heard as early as the twelfth week of pregnancy using a highly sensitive Doppler that allows us to hear the baby's heartbeat. The normal range for the baby's heart rate is 115 to 160 beats per minute. Fast or slow, the heart rate is not a valid indication of whether a baby is a girl or boy.

  • Weeks 1-6 - Discover the amazing changes that happen each week as your baby grows and develops, from a tiny cluster of cells all the way to becoming a squalling newborn.
  • Week 7 - From a few gathered cells, an embryo has grown in seven weeks to a collection of developing blood vessels, vertebrae and internal organs (including a kidney that produces urine). The embryo is now half an inch long. The fingers are webbed and spread like starfish. Toes begin to sprout and feet take shape. Facial features organize as the retinas form, eyelids begin to develop, and the palate and ear canals begin to take shape. In males, the penis begins to form. In girls, the clitoris and the ovaries appear.
  • Week 8 - The embryo now measures 16 millimeters, about the size of a postage stamp. It looks more like a fetus, curled in the familiar fetal position and its legs are extended and arms have defined, bent elbows. The developing eyelids begin to close up, the external ears have begun to form, the nostrils are defined and open and the upper lip has begun to form.
  • Week 9 - The embryo measures 1.25 inches from crown to rump and weighs 1/30 of an ounce. Taste buds develop, the toes separate, and the intestines move out of the umbilical cord and fully into the embryo's body. All the organs are in place and distinctly formed. Now they must grow in size and become interconnected. As they do, the embryo becomes a fetus.
  • Week 10 - With all organs in place, your baby shifts its energy from developing into growing over the next seven months until it is a full-size, full-term infant. Tiny fingernails and toenails have begun to grow, and hair follicles develop below the surface of the skin. The head is large and round, and the neck is visible beneath the tucked head. In males, the penis bud is clear. In females, genitalia have begun to show.
  • Week 11 - Between weeks 9 and 12, your baby doubles in size to three inches from head to toe. The connections between the nerves and the muscles have tripled since last week. Teeth begin to take shape. About 70 grams of amniotic fluid bathe your baby.
  • Week 12 - At the end of the first trimester, your baby weighs about 1/10 of an ounce. All of her major systems are in place, and all of her organs are formed and functioning. Now they begin the long, seven-month road to functioning outside the womb. Individuality is already present, as different babies have different facial expressions.

Bleeding and Cramping

Spotting in early pregnancy can be common along with some cramping with or without spotting. The cervix is more vascular during pregnancy and can bleed easily sometimes after intercourse or a cervical exam. Some mild cramping may also be common in early pregnancy as attachment takes place within the uterus. If you experience spotting or cramping, we still want you to call the office to speak with a nurse so they can better assess the situation. If it is after office hours, you may call the office number and you will be forwarded to speak with a registered nurse through MyNurse.

Morning Sickness

Nausea and vomiting are common complaints during the first 3 months of pregnancy and are usually due to hormonal changes occurring in your body. About half of all pregnant women experience this problem. Nausea may start about the sixth or seventh week, but seldom continues beyond the end of the third month.

Although, often called morning sickness, nausea and vomiting may occur at any time of the day.

You may find some relief by eating dry cereal, a piece of toast, or a cracker about a half hour before getting out of bed in the morning and move slowly when you get up. Let plenty of fresh air into the house to get rid of cooking and other household odors.

Divide your food into five small meals a day rather than three large ones, as keeping food in your stomach seems to control nausea. Avoid greasy and spicy foods or any foods that may disagree with you. Drinking liquids between meals instead of with your food may help.

Fatigue (Weakness)

Fatigue is a natural occurrence in pregnancy; it results from the hormonal and other changes in your body. Also, anemia (low red blood cells) may cause fatigue and point out the need for increased iron intake. Pregnancy places many demands on your body, and it is normal to often feel tired. It is important to get both regular exercise and enough rest at night. Exercise helps you maintain a healthy weight and flexibility; it stimulates circulation and also fights fatigue and depressed mood. It is not unusual to find your energy returning as you move through the middle months of pregnancy.


Eat about 300 more calories than you normally eat. Healthy foods such as fresh fruits, vegetables and whole grains are a great choice. Stay away from fast foods as they are high in fats and salt. Limit your caffeine intake. Increase your calcium intake to 1500mg per day. Stay away from unpasteurized cheese and dairy (feta, goat cheese, blue cheese, etc.), undercooked meats, and fish with high levels of mercury (shark, swordfish, tilefish, and king mackerel).


Pregnancy can be an emotional roller coaster for some women; mood swings, irritability, irrational thoughts, and tearfulness are not unusual. It is also common to feel disorganized and to have trouble concentrating. Talk to your provider if you are troubled by how you feel emotionally.

Exercise During Pregnancy

Mild to moderate physical activity is beneficial to pregnant women and will not harm the baby. Women who have not exercised regularly before becoming pregnant should not now begin a vigorous exercise program (high impact aerobics, cycling, jogging, etc.), but may do some low-key exercising. The following important points should be considered when you reflect on the benefits of regular exercise during pregnancy.

  • If you have some complications during your pregnancy you will probably be advised not to exercise. Talk to your provider about your special needs.
  • Begin and end exercise with a warm up and cool down time. Avoid exercising in hot weather.
  • Be sure to drink plenty of fluids.
  • Monitor your level of activity moderate exercise is fine (walking, swimming, low impact aerobics, etc.); avoid hard or extreme levels of activity. Stop if you feel dizzy, faint, short of breath, or significant cramping.


Nasal congestion, fatigue, eyestrain, caffeine withdrawal, anxiety, and tension are all possible causes of headaches during pregnancy (and other times). Rest and relaxation are often the most effective remedies for headaches.

For headaches of the sinus type, press a hot, moist towel over your eyes and forehead. If nasal congestion is part of the problem, a humidifier or hot shower may help.

If headache persists or is accompanied by changes in vision, right upper quadrant pain, swelling of face and or hands, notify your provider immediately.

Pregnancy is not the time to have new glasses or contact lenses fitted, and the lenses that were fine before you became pregnant might cause headache or strain now. Your body's increased volume of circulation during pregnancy can affect your vision, but be reassured that these problems are only temporary.

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Up Next: Second Trimester (Weeks 13-26)

Learn what to expect during the next trimester, including pregnancy weight gain, dizziness and fainting and first fetal movement. 

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