First Trimester of Pregnancy

Key Highlights for the First Trimester

The first trimester is an emotional rollercoaster filled with moments of joy, anxiety, excitement and dread. And the physical changes are just as dramatic. Your body is working overtime to grow new life, and major things are happening on a cellular level every single day. (By the end of your first trimester, several of baby’s major organs will have started to form, and you’ll be able to see baby move and groove via ultrasound!) It’s no wonder the first three months are underscored by extreme exhaustion and other less-than-pleasant symptoms (hello, morning sickness and constipation). No one said pregnancy would be easy, so find an OB or midwife you trust, and keep up with prenatal visits and important screenings and tests. The first trimester can feel overwhelming; just take it one day, and milestone to-do, at a time. You’ve got this!

How Long Is the First Trimester?

It might feel like the first trimester stretches on for an eternity, but in reality it starts on day one of your last menstrual period and extends through week 13, day 6. Yes, this means the first trimester includes a brief period when you’re not yet biologically pregnant. It’s a bit confusing, but your medical provider will use the timing of your last period to determine your due date. That means fertilization technically happens around week 2 or 3 and implantation occurs around week 4—so you’ll probably be able to get a positive pregnancy test around week 5. This timeline isn’t definitive, but there’s something reassuring about knowing that the first trimester is well underway by the time you get that positive result.

First Trimester Symptoms

The early weeks and months of pregnancy can be physically and emotionally taxing. Those first trimester hormones are no joke, and your body is working hard to grow a human. This means you might feel less than stellar for a while. Of course, pregnancy is a pretty subjective experience. Some pregnant people will have all the symptoms, while others will carry on feeling more or less like their normal, pre-pregnant selves. Odds are, though, you’ll experience at least one or two of the most common first trimester symptoms, including:

Morning sickness

Got that queasy feeling in your tummy? Retching or vomiting is a common affliction in early pregnancy, affecting anywhere from 50 to 90 percent of moms-to-be. A result of rising hCG hormones in your system, morning sickness typically starts a week or two after your missed period and peaks around 9 or 10 weeks. While nagging nausea can persist well beyond the first trimester, most pregnant people get significant relief by week 15. In the meantime, try to hang in there. Eating small, frequent meals can help, as can nibbling on bland carb-centric foods. While you’re at it, be sure to take your daily prenatal vitamin with a mini meal, as this can make a difference too. Need more nausea-quelling tips? Head here for relief.

Bloating and constipation

Well before that adorable bump appears, you’ll feel like your belly has expanded. But in the early weeks of pregnancy, that’s not baby—that’s just bloat. Progesterone, another key pregnancy hormone, relaxes muscles in the gastrointestinal tract, causing a sluggish gut and slow-working digestive system. That can mean uncomfortable gas, bloating and constipation. This is common early in pregnancy but will also come and go throughout the coming trimesters.

Sore breasts

Your breasts may get the memo that you’re pregnant before you do. In fact, they may feel sore as early as two weeks after conception, thanks to a surge in hormones and increased blood flow. This is just the tip of the iceberg; you can expect lots of breast changes throughout the next nine+ months, as your body prepares to birth and potentially feed a tiny new person.

Baby Development in the First Trimester

You may not look pregnant for a while, but a lot is happening behind the scenes—and that veritable seed inside your belly will grow by leaps and bounds throughout the next 13 weeks. Cells differentiate to become organs and systems of baby’s body, including the lungs, heart, brain, liver, spine, limbs and genitalia. What’s more, baby’s adorable facial features, toes and even fingernails begin to form in the first trimester.

What to Avoid During the First Trimester

Pregnancy isn’t all fun and games, and there are a few hard rules you’ll have to follow. Here are some things you’ll want to avoid in the coming weeks and months:

• Smoking and recreational drugs. For starters, you’ll want to quit smoking and cut out any other habits that could pose a danger to baby, such as marijuana or other recreational drug use.
• Alcohol. Alcoholic beverages are off the table for the next nine+ months. No amount of alcohol is considered safe during pregnancy.
• Certain foods. Now that you’re pregnant, food-borne illnesses can be particularly harmful. To keep you and baby safe, doctors recommend avoiding foods that can contain bacteria and parasites, including raw meat, fish and eggs; unpasteurised cheese and juice; high-mercury seafood; unwashed vegetables; cold cuts and prepared deli foods. Caffeine is okay in moderation—up to 200 mg a day.
• Certain chemicals and ingredients. It’s time to take a hard look at the ingredient lists of your skincare, beauty and cleaning products, and avoid things like toxic paint fumes and even kitty litter.
• Hot tubs, saunas and steam rooms. A long soak or sweat might sound like a heavenly way to rest your tired body, but you’ll want to avoid anything that could raise your core body temperature higher than 102 degrees Fahrenheit, which can be extremely dangerous for your developing baby.

What's Coming Next?

Second TrimesterThird TrimesterFourth Trimester

First Trimester Videos

Sit back and watch videos that cover all things pregnancy. We offer tips and tricks to help you take on your first trimester with confidence.

First Trimester Tools

Whether you need help choosing baby’s name or figuring out your due date, our tools are here to help. Check out our Baby Name Finder, Due Date Calculator, and even a Chinese Gender Chart.

Planner+Baby Name FinderChinese Gender ChartDue Date Calculator

Community Forums

Want to connect with other parents and parents-to-be like you? Join our first trimester forums and birth month clubs to strike up conversations, ask questions and find advice and support from others.