Conception typically occurs about two weeks after your period begins. To calculate your due date, your health care provider will count ahead 40 weeks from the start of your last period. This means your period is counted as part of your pregnancy — even though you weren’t pregnant at the time
Week 3: Fertilization
The sperm and egg unite in one of your fallopian tubes to form a one-celled entity called a zygote. If more than one egg is released and fertilized, you may have multiple zygotes.
The zygote has 46 chromosomes — 23 from you and 23 from your partner. These chromosomes will help determine your baby’s sex, traits such as eye and hair color, and, to some extent, personality and intelligence.
Soon after fertilization, the zygote travels down the fallopian tube toward the uterus. At the same time, it will begin dividing rapidly to form a cluster of cells resembling a tiny raspberry. The inner group of cells will become the embryo. The outer group of cells will become the membranes that nourish and protect it.
Week 4: Implantation
When the zygote — now known as a blastocyst — reaches your uterus, it will burrow into the uterine wall for nourishment. The placenta, which will nourish your baby throughout the pregnancy, also begins to form.
By the end of this week, you may be celebrating a positive pregnancy test.
Week 5: The embryonic period begins
The embryo is now made of three layers. The top layer — the ectoderm — will give rise to your baby’s outermost layer of skin, central and peripheral nervous systems, eyes, inner ear, and many connective tissues.The fifth week of pregnancy, or the third week after conception, marks the beginning of the embryonic period. This is when the baby’s brain, spinal cord, heart and other organs begin to form.
Your baby’s heart and a primitive circulatory system will form in the middle layer of cells — the mesoderm. This layer of cells will also serve as the foundation for your baby’s bones, muscles, kidneys and much of the reproductive system.
The inner layer of cells — the endoderm — will become a simple tube lined with mucous membranes. Your baby’s lungs, intestines and bladder will develop here.
By the end of this week, your baby is likely between 1/16 and 1/8 inch (1.5 to 3 millimeters) long — about the size of the tip of a pen.
Week 6: The neural tube closes
Growth is rapid this week. Just four weeks after conception, the neural tube along your baby’s back is closing and your baby’s heart is pumping blood.
Basic facial features will begin to appear, including passageways that will make up the inner ear and arches that will contribute to the jaw. Your baby’s body begins to take on a c-shaped curvature. Small buds will soon become arms and legs.
By the end of this week, your baby may be 1/6 to 1/4 inch (4 to 6 millimeters) long.
Week 7: Baby’s head develops
Seven weeks into your pregnancy, or five weeks after conception, your baby’s brain and face are rapidly developing. Tiny nostrils become visible, and the eye lenses begin to form. The arm buds that sprouted last week now take on the shape of paddles.
By the end of this week your baby may be 1/4 to 1/3 inch (7 to 9 millimeters) long — a little bigger than the top of a pencil eraser.
Week 8: Movement begins
Eight weeks into your pregnancy, or six weeks after conception, your baby’s arms and legs are growing longer, and fingers have begun to form. The shell-shaped parts of your baby’s ears also are forming, and your baby’s eyes and nipples are visible. The upper lip and nose have formed. The trunk of your baby’s body is beginning to straighten.
Your baby may begin to move this week, but you won’t be able to feel it yet.
By the end of this week, your baby may be about 1/2 inch (11 to 14 millimeters) long.
Week 9: Baby’s toes form
In the ninth week of pregnancy, or seven weeks after conception, your baby’s arms grow, develop bones and bend at the elbows. Toes begin to form, and your baby’s eyelids and ears continue developing.
By the end of this week, your baby may be close to 3/4 inch (18 to 22 millimeters) long.
Week 10: Baby’s neck begins to develop
By the 10th week of pregnancy, or eight weeks after conception, your baby’s head has become more round. The neck begins to develop, and your baby’s eyelids begin to close to protect his or her developing eyes.
Although the genitals are developing, it’s still too soon to identify your baby’s sex.
Week 11: Baby’s genitals develop
At the beginning of the 11th week of pregnancy, or the ninth week after conception, your baby’s head still makes up about half of its length. But your baby’s body is about to catch up, growing rapidly in the coming weeks.
Your baby is now officially described as a fetus. This week your baby’s eyes are widely separated, the eyelids fused and the ears low set. Red blood cells are beginning to form in your baby’s liver. By the end of this week, your baby’s external genitalia will start developing into a penis or clitoris and labia majora.
By now your baby may measure about 2 inches (50 millimeters) long from crown to rump and weigh almost 1/3 ounce (8 grams).
Week 12: Baby’s fingernails develop
Twelve weeks into your pregnancy, or 10 weeks after conception, your baby is developing fingernails. Your baby’s face now has a human profile.
By now your baby may be nearly 2 1/2 inches (61 millimeters) long from crown to rump and weigh about 1/2 ounce (14 grams).
What to Expect
- Tender breasts. Increased hormone production may make your breasts unusually sensitive. Your breasts will probably feel fuller and heavier. Wearing a more supportive bra or a sports bra may help.
- Bouts of nausea. Many women have queasiness, nausea or vomiting in early pregnancy — probably due to normal hormonal changes. Nausea tends to be worse in the morning, but it can last all day. To help relieve this first trimester pregnancy symptom, eat small, frequent meals throughout the day. Choose foods that are low in fat and easy to digest. It’s also helpful to drink plenty of fluids. Avoid foods or smells that make your nausea worse. Try drinking ginger ale. For some women, motion sickness bands are helpful. For others, alternative therapies such as acupuncture or hypnosis offer relief. If you’re considering an alternative therapy, get the OK from your health care provider first.
Morning sickness is a misnomer, since it can strike at any time of the day or night. Most women who experience morning sickness notice a dramatic improvement after the first trimester — at roughly 13 weeks. But some women have nausea and vomiting beyond the first trimester. Also, morning sickness may be more severe if this is your first pregnancy or if you’re carrying multiple fetuses.
Some simple steps that may be helpful in relieving nausea and vomiting:
- Eat smaller meals or snacks frequently throughout the day.
- Before getting out of bed in the morning, eat a couple of soda crackers or a dry piece of toast.
- Have a small snack at bedtime or when you wake up to go to the bathroom in the middle of the night.
- Avoid greasy, rich, fatty and spicy foods.
- Suck on hard candy.
- Wear an acupressure wrist band. Some studies have shown a benefit from acupressure and acupuncture in relieving nausea.
Because you lose fluids when you throw up, it is important to stay hydrated. Try sucking on ice chips or ice pops. Take frequent small sips of water instead of drinking a whole glass of water all at once. Some women find that taking small sips of ginger ale or peppermint tea relieves their symptoms. Check with your doctor before using any natural remedies alleged to relieve nausea and vomiting during pregnancy.
Certainly, throwing up several times a day may make it more difficult for you to retain adequate fluids — which is a health concern for you and your baby. Call your doctor if:
- You have not been able to keep liquids down for more than one day.
- You’re vomiting blood, which may appear bright red or look like black coffee grounds.
- You lose more than 2 pounds.
- You have vomited more than four times in one day.
Severe morning sickness (hyperemesis gravidarum) may require a stay in the hospital and treatment with intravenous (IV) fluids and medications, including anti-emetics, which control nausea. Rarely, severe or persistent nausea or vomiting may be caused by a medical condition unrelated to pregnancy, such as thyroid, liver or gallbladder disease.
Contact your health care provider if the nausea is severe, you’re passing only a small amount of urine or it’s dark in color, you can’t keep down liquids, you feel dizzy or faint when standing up, your heart is racing, or you vomit blood.
- Unusual fatigue. You may feel tired as your body prepares to support the pregnancy. Your heart will pump faster and harder, and your pulse will quicken. To combat fatigue, rest as much as you can. Make sure you’re getting enough iron and protein. Include physical activity, such as a brisk walk, in your daily routine.
- Increased urination. You may need to urinate more often as your enlarging uterus presses on your bladder. The same pressure may cause you to leak urine when sneezing, coughing or laughing. To help prevent urinary tract infections, urinate whenever you feel the urge. If you’re losing sleep due to middle-of-the-night bathroom trips, drink less in the evening — especially fluids containing caffeine, which can make you urinate more. If you’re worried about leaking urine, panty liners may offer a sense of security.
- Heartburn and constipation. During first trimester pregnancy, the movements that push swallowed food from your food pipe into your stomach are slower. Your stomach also takes longer to empty. This slowdown gives nutrients more time to be absorbed into your bloodstream and reach your baby. Unfortunately, it may also lead to heartburn and constipation. To prevent heartburn, eat small, frequent meals and avoid fried foods, carbonated drinks, citrus fruits or juices, and spicy foods. To prevent or relieve constipation, include plenty of fiber in your diet and drink lots of fluids. Regular physical activity also may help.
- Normal circulatory changes in early pregnancy may leave you feeling a little dizzy. Stress, fatigue and hunger also may play a role. To prevent mild, occasional dizziness, avoid prolonged standing. Rise slowly after lying or sitting down. If you start to feel dizzy while you’re driving, pull over. If you’re standing when dizziness hits, sit or lie down. Seek prompt care if the dizziness is severe and occurs with abdominal pain or vaginal bleeding. This may indicate an ectopic pregnancy — a condition in which the fertilized egg implants itself outside the uterus. To prevent life-threatening complications, the ectopic tissue must be removed.