Your First Trimester of Pregnancy, Week-by-Week

From when to expect common pregnancy symptoms to what size your baby will be each week, here's everything you need to know about your first trimester of pregnancy.

A lot happens during the first trimester of pregnancy, even before you even know you're actually pregnant. Some of the most crucial development happens in the first few weeks of pregnancy, but when it's happening on such a small scale, it can be hard to comprehend what's actually going on inside your body. So here's a breakdown of what happens in the first trimester of pregnancy, week-by-week.

01 of 13

Week 1

week 1 pregnant uterus

You're actually not pregnant yet—the clock starts ticking on the first day of your last period. So even though pregnancies are said to be 40 weeks long, you only carry your baby for 38 weeks.

If you're trying to conceive, start taking a daily prenatal vitamin with at least 400 micrograms of folic acid; this B vitamin has been shown to help prevent neural-tube defects, such as spina bifida. It's also a good idea to talk to your doctor about decreasing any potentially hazardous habits, like smoking or drinking.

Read more about being one week pregnant.

02 of 13

Week 2

week 2 fertilization

Ovulation occurs during the second week of the first trimester. For the best chances of getting pregnant, have sex one to two days before your expected ovulation date.

Experts also recommend exercising for at least 30 minutes on most, if not all, days throughout pregnancy. There's no better time to start than now!

Read more about being two weeks pregnant.

03 of 13

Week 3

week 3 fertilization

You may be pregnant but probably won't have any symptoms. While it's early, it's a good idea to go over what prescription and over-the-counter medications are safe for you to take during pregnancy. It's especially recommended to avoid all products containing vitamin A or its derivatives, such as Retin-A or Accutane. That said, many health issues, such as asthma, diabetes, and many mental health conditions, require ongoing treatment, so talk to your doctor before discontinuing any necessary medications.

Get a flu shot if you haven't already; it's safe for pregnant people.

Read more about being three weeks pregnant.

04 of 13

Week 4

4 weeks pregnant fetus

At this point in the first trimester, you'll receive a positive pregnancy test! You may be starting to feel bloated, crampy, tired, and moody. Many pregnant people also experience sore breasts, nausea/vomiting, and a frequent need to pee this weekI But don't worry if you don't have any early pregnancy symptoms; that's completely normal too.

Wondering what to do now? Invest in an extra supportive bra, especially if your breasts are expanding. Many pregnant people with breasts grow a full cup size in the first few weeks.

It's also a good idea to cut down on potential dangers in your environment, such as secondhand smoke. If you're a feline owner, ask your partner to take over the litterbox duties as cat feces may harbor parasites that cause toxoplasmosis, an infection that can harm the fetus.

Read more about being four weeks pregnant.

05 of 13

Week 5

5 weeks pregnant fetus

Though the embryo is only about the size of a grain of sand, the heart is pumping blood, most other organs have begun to develop, and arm and leg buds appear. You may start to experience "pregnancy brain." If it helps, make lists at work and at home to keep organized.

Those who are five weeks pregnant should also make an appointment with their OB or midwife. Most caregivers want to see you for the first time between six and 10 weeks.

Read more about being five weeks pregnant.

06 of 13

Week 6

6 weeks pregnant fetus

Now that the pregnancy is feeling more real, you might worry about miscarriage. Reassure yourself that there's nothing you can do to cause a miscarriage. Some research links early pregnancy losses to consuming excessive caffeine daily, so it may be helpful to limit your intake to 200 mg or less each day.

Think about when you want to tell family, friends, and boss you're pregnant. Some people may choose wait until after the first trimester, when miscarriage risk drops, but there is no right or wrong time to announce your pregnancy; the choice is entirely up to you.

Read more about being six weeks pregnant.

07 of 13

Week 7

7 weeks pregnant fetus

The embryo doubles in size but is still less than a half-inch long. As your pregnancy hormones increase, morning sickness may be worsening. Or you may be ravenous 24/7.

If you're nauseated, try eating several small meals throughout the day (especially ones with ginger and citrus), avoid strong odors, and wear acupressure wristbands.

For some people, weight gain is only minimal in the first trimester, but morning sickness and cravings can be different for everyone, so be sure to listen to your body right now.

Read more about being seven weeks pregnant.

08 of 13

Week 8

8 weeks pregnant fetus

Your doctor may look or listen for the baby's heartbeat with an ultrasound around this stage. If you get a first trimester ultrasound, it usually also comes with an official due date—though very few people actually deliver on their due date.

Though your due date sounds very far away, you can always start reading up on baby care and preparing your living space now.

Read more about being eight weeks pregnant.

09 of 13

Week 9

9 weeks pregnant fetus

The pressure of your growing uterus on your bladder may cause you to leak small amounts of urine. To help strengthen your pelvic floor, you can start doing Kegels. Here's how: Squeeze the muscles around your vagina as if you're stopping the flow of urine. Do several at a time, a few times a day throughout pregnancy. They strengthen your pelvic-floor muscles, helping with incontinence while preparing your body for delivery.

Read more about being nine weeks pregnant.

10 of 13

Week 10

10 weeks pregnant fetus

Your inch-long baby is now called a fetus. While the icky side effects of pregnancy may be starting to abate, pregnancy testing might be starting to ramp up.

If you will be 35 or older when you deliver, you can make an appointment to discuss genetic screening or diagnostic tests, such as chorionic villus sampling (CVS). They look for certain birth defects and are usually done between 10 and 12 weeks. Your doctor's office may provide counseling; if not, ask for a referral to a genetic counselor.

Read more about being 10 weeks pregnant.

11 of 13

Week 11

11 weeks pregnant fetus

Your cravings may run the gamut from cheeseburgers to chalk (really!). Weird non-food cravings are known as pica and can reflect a deficiency in your diet. Call your doctor if you're experiencing pica.

Also make an appointment if you're having the nuchal translucency test, which screens for Down syndrome and other chromosomal abnormalities. The test must be done between 11 and 14 weeks.

Note that by week 11 of the first trimester, nearly all of the fetus's organs are beginning to function, and genitals begin to form.

Read more about being 11 weeks pregnant.

12 of 13

Week 12

12 weeks pregnant fetus

Your uterus has begun to expand outside the protective pelvic bones. It will increase in size almost 1,000 times by the end of your pregnancy! You may be starting to show now, especially if it's not your first baby.

From now on, steer clear of any activities that pose the risk of a fall or abdominal trauma, such as horseback riding. It's also helpful to avoid exercises that require you to lie flat on your back—your growing fetus can place too much weight on a major vein, causing reduced blood flow to the uterus.

Read more about being 12 weeks pregnant.

13 of 13

Week 13

13 weeks pregnant fetus

Now that you've finished your first trimester, you can plan on gaining about 12 pounds during the next 14 or so weeks. To support your baby's growth, aim to get 300 extra calories a day from healthy foods such as lean meats and poultry, eggs, vegetables, and whole grains.

Start shopping for maternity clothes. Many shops have belly bumps to help you size for what you might look like in later pregnancy.

Read more about being 13 weeks pregnant.

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