Your First Trimester of Pregnancy, Week-by-Week

Week 1 of Pregnancy

In obstetrics, it's common to use gestational age to measure how far along a pregnancy is starting from the first day of the person's last menstrual period rather than the precise date of conception, which is often not known. As a result, the first trimester actually starts before you're pregnant!

Although you're not pregnant yet at week one, the clock started ticking on the first day of your last period before you conceived.

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 health care provider about cutting out any potentially hazardous habits, like smoking.

Week 2 of Pregnancy

You're still not yet pregnant in the second week of your first trimester, though many people will ovulate around the end of this week if they have the average menstrual cycle length.

According to the American College of Obstetricians and Gynecologists (ACOG), people with 28-day cycles typically ovulate around day 14. If your cycles are typically shorter than 28 days, you may ovulate earlier this week; and if your cycles are typically longer, you'll likely ovulate next week.

If you're trying to conceive, getting pregnant is on your to-do list this week! Your fertile window is longer than just the day you ovulate—it actually lasts around six days. That's because sperm can live up to five days in the female reproductive tract, while your egg can survive for up to a day after ovulation. So, five days before ovulation and one day after are your best chances to conceive.

Experts also recommend exercising for at least 30 minutes on most, if not all, days throughout pregnancy. And while it is best to start exercising before conception, there is no reason you cannot begin walking or other appropriate exercise once you are pregnant. Just be sure to talk to a health care provider about what is best for you.

Week 3 of Pregnancy

By week 3 of the first trimester, you may be pregnant but probably won't have any pregnancy symptoms. It's around this week, that conception (when the egg is fertilized) occurs for most people.

It's an exciting time, but hold tight—it's still too early for a pregnancy test to turn up positive.

While it's early, reviewing what prescription and over-the-counter (OTC) medications are safe for you to take during pregnancy is a good idea. Avoiding products containing excessive vitamin A or its derivatives, such as Retin-A or Accutane, is especially recommended, as retinoids can cause congenital malformations.

That said, getting vitamin A through foods or your prenatal vitamin is important. Vitamin A helps support the vision needs of both you and your baby as well as promotes the maintenance of the fetal immune system.

As for other medications and supplements, many health issues, such as asthma, diabetes, and many mental health conditions, require ongoing treatment, so talk to a health care provider before discontinuing any necessary medications.

If you haven't already, this is also a good time to be sure you're up to date on your vaccines, especially the flu and COVID-19 shots. These vaccines are recommended during pregnancy because of the higher risks of complications in pregnant people.

Week 4 of Pregnancy

You may get a positive pregnancy test at this point in the first trimester! But don't worry if you don't; it's still early. Some people don't get that positive line until week five, especially if their cycles are longer or irregular.

You may start to feel very early pregnancy symptoms at this point, including:

• Sore breasts
• Fatigue
• Nausea or vomiting
• Bloating
• Cramping
  
• Moodiness
  
• Frequent urination
  

But don't worry if you don't have any symptoms just yet; that's completely normal too.

You may find that this is a good time to invest in an extra supportive bra. Many pregnant people grow a full cup size in the first few weeks of pregnancy. Wearing a comfortable, supportive bra (even during sleep) can help with the heaviness and soreness that can accompany early pregnancy.

It's also a good idea to reduce potential environmental dangers, such as secondhand smoke. If you have a cat, ask your partner to take over the litterbox duties, as cat feces may harbor parasites that cause toxoplasmosis, an infection that can harm a fetus.

Week 5 of Pregnancy

If you haven't already, by week five you'll likely have noticed your missed period and will probably get a positive pregnancy test. This week, the fertilized egg becomes an embryo.

The embryo is only about the size of an orange seed. At this time, the embryo's brain, spine, and heart start to develop.

You may start to experience "pregnancy brain," the brain fog, forgetfulness, or absentmindedness that can accompany pregnancy. So, if it helps, make lists at work and home to keep organized.

Those who are five weeks pregnant should also make an appointment with a health care provider for a first prenatal visit. Most providers will want to see you for the first time between six and 10 weeks depending on your medical history.

Week 6 of Pregnancy

Now that the pregnancy feels more real, you might worry about many things, including miscarriage, in the first trimester. This is understandable since when they happen, 80% of all miscarriages occur in the first trimester.

Reassure yourself that most miscarriages are not preventable. In other words, if you do experience a miscarriage, it is very likely you did nothing wrong to cause it, and there is probably nothing you could have done differently to avoid it.

Some research shows a link between some early pregnancy losses and consuming excessive caffeine, so limit your caffeine intake to 200 miligrams or less. Some other ways to lower your miscarriage risk include getting routine prenatal care, avoiding alcohol and smoking, managing chronic health conditions, and reviewing your medications with a health care provider.

Think about when you want to tell family, friends, and your employer that you're pregnant. Some people wait until after the first trimester when miscarriage risk drops, while others share early to have support in the event miscarriage happens. There is no right or wrong time to announce your pregnancy; the choice is entirely up to you.

Week 7 of Pregnancy

The embryo doubles in size by week seven but is still less than a half-inch long. As your pregnancy hormones increase, morning sickness may worsen. 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)
• Avoiding strong odors
• Wearing acupressure wristbands

In the first trimester, morning sickness and cravings can differ for everyone, so be sure to listen to your body right now.

Week 8 of Pregnancy

Your health care provider may look or listen for fetal cardiac activity with an ultrasound around this stage. If you get a first-trimester ultrasound, it usually also comes with an estimated due date—though very few people actually deliver on their due date. Research has found only about 5% of people give birth on their due dates. You can also use a due date calculator to estimate your baby's arrival time.

Though your due date sounds very far away, you can always start reading up on baby care and preparing your living space now. Thinking about the baby's nursery and how you want to decorate it can be a really fun way to prepare.

This can also be an excellent time to consider which childbirth classes are right for you. Maybe a hospital class fits the bill, or an independent class like Bradley, Hypnobirthing, or Lamaze is a better fit.

Week 9 of Pregnancy

By week nine of your first trimester, the pressure of your growing uterus on your bladder may cause you to leak small amounts of urine. You may also find yourself waking up multiple times a night to use the bathroom.

While this is most common in the third trimester, it can occur any time due to hormonal changes (relaxin and progesterone), more lax ligaments, and relaxing pelvic floor muscles.

To help strengthen your pelvic floor, you can start doing pelvic floor exercises. Those may include Kegels, which require you to squeeze the muscles that support the uterus, bladder, small intestine, and rectum (feeling as if you're stopping the flow of urine).

These exercises can strengthen your pelvic floor muscles, helping with incontinence while preparing your body for giving birth. But it's important to do Kegels and all pelvic floor exercises correctly. If you have trouble, a health care provider, childbirth educator, or pelvic floor therapist can help.

Week 10 of Pregnancy

Your inch-long baby is now called a fetus. While some of the icky side effects of pregnancy like morning sickness and breast tenderness may start to abate, prenatal testing might ramp up.

If you are 35 or older or your provider recommends it, you can make an appointment to discuss genetic screening or diagnostic testing, such as noninvasive prenatal tests (NIPT) or chorionic villus sampling (CVS).

Screening tests like NIPT determine whether your fetus is at risk for certain genetic conditions, while diagnostic tests like CVS can detect certain congenital disorders. These tests are usually done at the end of the first trimester—between 10 and 12 weeks.

Your health care provider's office may provide genetic counseling. If not, ask for a referral to a genetic counselor.

Week 11 of Pregnancy

Your pregnancy 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 provider if you're experiencing pica.

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

By week 11 of the first trimester, fetal organs are beginning to develop, and genitals begin to form.

Week 12 of Pregnancy

Your uterus has begun to expand outside the protective pelvic bones. It will increase many times its size by the end of your pregnancy! You may be starting to show now, especially if this isn't your first pregnancy.

From now on, be mindful of activities that pose the risk of a fall or abdominal trauma, such as horseback riding. It's also helpful to start avoiding 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. Though this suggestion usually is not initiated until 16 weeks of pregnancy, it can be helpful to get into the practice.