Pregnancy week by week.

Your baby: Pregnancy is counted from the first day of your last period, so for the first two weeks you aren’t pregnant yet. Around the end of week 2 an egg is released. If it joins with sperm, your baby’s life begins as a single cell that already carries a full set of DNA. Over the next several days that cell divides and travels to the uterus.

You: You won’t feel different yet. If you could become pregnant, take 400 micrograms of folic acid every day: the CDC says serious birth defects of the brain and spine happen in the first few weeks, often before you know you’re pregnant.

Your baby: The tiny ball of cells that is your baby settles into the lining of your uterus.

You: This is about when a period is missed. Home pregnancy tests are most accurate starting the day after a missed period, and more accurate a week later.

This week: Call a clinic or midwife to set up your first prenatal visit, and take 400 micrograms of folic acid every day.

Your baby: Your baby’s brain, spinal cord and heart begin to form. Clinicians use the word embryo from now through week 10.

You: The pregnancy hormone hCG is rising, which is what a pregnancy test picks up. You may notice tender breasts, tiredness, or needing to pee more often.

This week: Stop alcohol completely: the CDC says there is no known safe amount during pregnancy. If you smoke or vape, call 1-800-QUIT-NOW for free help quitting.

Your baby: Around weeks 6 to 7 your baby’s heart beats in a regular rhythm, which can be seen on a vaginal ultrasound. The neural tube, which becomes the brain and spinal cord, is closing, and small buds that will become arms appear.

You: Nausea, with or without vomiting, is common in the first trimester. Severe nausea and throwing up is a reason to call your clinician right away.

This week: Health coverage makes everything easier. See Sign up early, below.

Your baby: Leg buds appear, and your baby’s brain and face are growing quickly.

You: Foods and smells you used to like may turn your stomach, and you may crave others.

This week: Write down the first day of your last period and every medicine and supplement you take, and bring the list to your first visit.

Your baby: Your baby’s hands and feet look like tiny paddles, with fingers starting to form, and the lungs begin to develop. Your baby is about half an inch to an inch long.

You: Tiredness can be intense in these weeks. Rest when you can.

This week: A first prenatal visit before 10 weeks is a good goal. An ultrasound in the first trimester is the most accurate way to confirm how far along you are.

Your baby: Toes can be seen, and elbows appear.

You: Mood swings, headaches, heartburn and constipation are all common in the first trimester.

This week: Be careful with a few foods. A healthy pregnancy lists what to avoid.

Your baby: Your baby’s fingers and toes lose their webbing, and every major organ has begun to form. After this week, clinicians use the word fetus until birth.

You: Your clinician may offer screening tests between weeks 10 and 13 that look at the chance of certain conditions. A screening test shows a higher or lower chance, not a diagnosis, and having one is your choice.

This week: Whatever a result shows, you and your baby deserve support. Ask us privately if you’d like help finding it.

Your baby: Your baby’s eyelids close to protect the developing eyes, and they stay closed until about week 28. The kidneys begin to make urine.

You: You may gain a little weight in the first trimester, or lose a little if nausea has been strong.

Your baby: Fingernails are forming. Your baby is about 2 to 3 inches long and weighs about half an ounce to an ounce.

This week: If it’s flu season, ask about a flu shot. The CDC recommends flu vaccination during any trimester of pregnancy.

Your baby: Your baby’s bones are hardening, especially the long bones of the arms and legs.

You: This is the last week of the first trimester. For many women, nausea and tiredness start to ease from here.

Your baby: Around now, whether your baby is a boy or a girl becomes clearer. It can often be seen at the ultrasound done between weeks 18 and 22.

You: Many women find the second trimester easier than the first, as nausea and tiredness fade.

Your baby: Your baby moves arms and legs in coordinated ways that can be seen on ultrasound, though the movements are still too small for you to feel.

You: As your belly grows, you may notice aches in your back, belly, groin or thighs.

Your baby: Your baby makes sucking motions with the mouth. Your baby is about 4 to 5 inches long and weighs about 3 to 4 ounces.

You: Stretch marks may appear, and the skin around your nipples may darken.

Your baby: Your baby’s digestive system is starting to work.

You: A dark line may appear on your skin from your belly button down, and some women get darker patches on the face. Both are common.

Your baby: Around weeks 18 to 20 your baby may begin to hear.

This week: The anatomy ultrasound is usually done between weeks 18 and 22. It looks closely at your baby’s body and growth, and you can often find out whether you’re having a boy or a girl, if you want to know.

Your baby: A waxy coating called vernix forms to protect your baby’s skin.

You: You may feel your baby move for the first time around weeks 19 to 21. Early movement often feels like a flutter.

Your baby: Your baby can hear and swallow, and is more active. Your baby is about 6 inches long and weighs about 9 to 11 ounces.

You: You’re about halfway to your due date. If you haven’t felt movement yet, you may begin to around now.

Your baby: Fine, soft hair called lanugo covers your baby’s body.

You: Some swelling in your ankles, fingers and face is common. Sudden or extreme swelling, or gaining a lot of weight very quickly, is a reason to call right away: it can be a sign of preeclampsia.

Your baby: Your baby’s eyebrows and hair can be seen.

You: Your hands may feel numb or tingly, and your skin may itch as your belly stretches. Call your clinician about severe itching, especially on your palms or the soles of your feet or at night, and about itching that comes with nausea, vomiting, loss of appetite, yellowing skin or exhaustion. These can be signs of a liver problem that needs care.

Your baby: The ridges that become fingerprints and footprints are forming. Between about weeks 23 and 28, the lungs start making surfactant, which will help them fill with air after birth.

Your baby: Your baby is about 12 inches long and weighs about a pound and a half. The lungs are formed but can’t yet work on their own.

This week: A blood sugar test for gestational diabetes is usually done between weeks 24 and 28.

Your baby: Your baby may respond to familiar sounds, like your voice, and startle at a loud noise.

This week: Talk, read and sing to your baby. Dad’s voice counts too.

Your baby: All the parts of your baby’s eyes are formed.

This week: If you work, start planning your leave. Washington’s Paid Family and Medical Leave asks you to give your employer written notice 30 days ahead. See Sign up early.

Your baby: Around weeks 27 to 28 your baby’s eyelids can open.

You: This is the last week of the second trimester.

This week: The CDC recommends the Tdap vaccine between weeks 27 and 36 of every pregnancy, preferably early in that window. It helps protect your newborn from whooping cough.

Your baby: Your baby practices breathing movements, which can be seen on ultrasound. Your baby is about 15 inches long and weighs about 2¼ to 2½ pounds.

You: From now on, pay attention to how your baby moves. The federal Office on Women’s Health suggests keeping track after 28 weeks, and the CDC says a change from what’s normal for your baby is what matters. If movement slows or stops, call right away.

This week: If your blood type is Rh-negative, a shot of Rh immune globulin is usually given around week 28. This is also a good time to sign up for a childbirth class.

Your baby: Your baby can kick, stretch and grasp.

You: Shortness of breath, heartburn and trouble sleeping are common in the third trimester.

Your baby: Your baby’s bone marrow is making red blood cells.

This week: Living on Orcas? Settle your plan for getting to the hospital now. Read Having a baby on Orcas.

Your baby: Most of your baby’s major development is finished. From here, the main job is gaining weight, and it happens quickly.

You: Your breasts may leak a little early milk, called colostrum.

Your baby: Your baby’s eyes can sense light, and the soft hair that covered the body starts to fall away. Your baby is about 15 to 17 inches long and weighs about 4 pounds.

This week: In RSV season, the CDC recommends one dose of the RSV vaccine between weeks 32 and 36 to protect your baby after birth. An antibody shot for your baby is the other option, and most babies don’t need both.

Your baby: Your baby’s bones are hardening, but the skull stays soft and flexible.

You: You may feel tightenings that come and go. Before 37 weeks, contractions every 10 minutes or more often are a sign of preterm labor: call right away.

Your baby: Your baby’s fingernails have grown to the fingertips.

This week: Pack a bag for the hospital and install the car seat. Babies ride rear-facing from the first trip home.

Your baby: Your baby has less room to move now.

You: Less room doesn’t mean less movement is OK. If your baby moves less than usual, call right away.

Your baby: Most babies have turned head-down by now, or will soon. Your baby is about 18 inches long and weighs about 6 pounds.

You: Visits are usually weekly from here.

This week: A test for group B strep is done at week 36 or 37. If it’s positive, you’ll get antibiotics during labor to protect your baby.

Your baby: Weeks 37 and 38 are called early term. Your baby’s lungs, brain and nervous system are still finishing their growth.

You: The CDC says that unless there is a medical need, a delivery should not be scheduled before 39 weeks.

This week: Learn the signs of labor, and keep your phone charged and your ride lined up.

Your baby: Your baby is still gaining weight and finishing the last stretch of growth before full term.

You: You may feel your baby drop lower in your belly, and your cervix begins to thin and soften as birth gets closer.

Your baby: At 39 weeks your baby is full term, and the organs are ready to work on their own.

You: Contractions that get stronger and closer together, your water breaking, or a bloody mucus discharge are signs of labor.

Your baby: Most babies are born 19 to 21 inches long and weigh between 6 and 9 pounds.

You: Only about 1 in 20 babies arrive on their due date. Most are born between 38 and 41 weeks.

This week: Keep your appointments, and call if your baby moves less than usual.

Your baby: Week 41 is called late term, and from 42 weeks a pregnancy is post-term.

You: Going past your due date is common. Stay in close touch with your clinician about the plan from here.

This week: Keep watching your baby’s movements, and call right away if they slow or stop.