What To Expect in the First Trimester Week By Week

The first few weeks of pregnancy can feel like a whirlwind—new, unfamiliar symptoms and the excitement (and anxiety) of realizing that your body is about to undergo massive changes. Many find this early window the most overwhelming: you’re navigating fatigue, nausea, new food aversions, changes in your sleep regimen, and trying to figure out what’s normal and what’s not. The good news? Most of what you’re experiencing is completely expected. 

But, for even more reassurance, here’s what to expect in the first trimester week by week in your early pregnancy, including what’s happening with your baby’s development, the changes you may notice in your body, and simple ways to support a healthy pregnancy (including a few tips for getting through the less glamorous parts… yes, nausea included).

Before we dive into the week-by-week details, it helps to understand the timeline of early pregnancy. The first trimester lasts from week 1 through week 13, with the second trimester beginning at week 14. Most patients first learn they’re pregnant around 4 weeks through an at-home pregnancy test or via a blood test from your fertility care team if you’ve been supported by a clinic.

Pregnancy symptoms can start before you even fully process that positive pregnancy test, in the first 4 to 5 weeks. Rising levels of hCG and progesterone are already signaling the body to support the pregnancy, which can lead to some very early changes for some. Remember—it’s also normal not to feel anything very early on!

Fatigue is one of the most common symptoms—many feel unusually tired. Other symptoms like breast tenderness or heaviness, mild cramping, and bloating are also common as the uterus and hormones begin to shift in preparation for pregnancy. You may notice a heightened sense of smell, food aversions, or mild nausea, though for many, nausea doesn’t peak until a bit later, around 6 to 9 weeks. You may also find yourself going to the bathroom more often as hormonal changes increase blood flow to the kidneys (making you have to pee more).

Every pregnancy is different—some feel several symptoms right away, while others feel almost nothing at all in these early weeks, and both experiences can be completely normal.

If you’re seeing a fertility specialist, the first ultrasound is typically around 5 to 6 weeks of pregnancy to confirm the pregnancy is in the uterus and progressing normally. If you got pregnant without the help of a clinic, the first ultrasound is often scheduled a bit later—usually around 8 to 10 weeks—when the embryo is larger and a heartbeat can be more reliably seen. Both approaches are normal; the difference simply reflects how closely early pregnancies are monitored in fertility care versus routine prenatal care.

If you’ve been trying to conceive on your own and you see that positive pregnancy test, the first reaction is often a mix of excitement, disbelief, and a lot of questions. The next step is usually to call your OB/GYN or family doctor to let them know you’ve had a positive home pregnancy test. In many practices, you won’t need to come in immediately—home tests can be very accurate, and your provider will typically schedule your first prenatal visit and ultrasound around 8 to 10 weeks of pregnancy. 

It’s also completely normal to feel anxious during this waiting period. Many wish they could get their first appointment done sooner, but this early window is largely about giving the pregnancy time to develop so that your first ultrasound can provide the most reassuring and useful information. of pregnancy. 

• Symptoms may be starting

• Hormones are adjusting to support fetal growth

• Size: 1 to 2 mm

• Gestational sac (manages nutrients before the placenta is formed) and yolk sac (supports early embryo development) may be seen on ultrasound

• The embryo is likely not visible yet

By weeks 6 to 7, many of the early symptoms of pregnancy become more noticeable as hormone levels—especially hCG and progesterone—rise quickly. This is the time when nausea and vomiting (a.k.a. morning sickness) commonly begin or intensify. Fatigue often continues and can feel more pronounced as your body works to support the rapidly developing placenta and embryo.

You may also continue to feel breast tenderness, more frequent urination, bloating, and stronger food aversions or cravings. Some people notice heightened emotions or mood swings, which are also driven by the intense hormonal shifts your body is equilibrating to. Mild pelvic cramping or lower abdominal pulling sensations can occur as the uterus begins to expand, but significant pain or heavy bleeding is not expected and should always prompt a call to your provider. While symptoms can feel overwhelming during this stage, they are usually a reflection of the normal hormonal changes that help sustain an early pregnancy.

• Hormones keep adjusting
• More or heightened pregnancy symptoms
• Mood swings

• Size: 3 to 5 mm
• The fetal pole (the first visible sign of a developing embryo) is often visible at this milestone
• You may be able to see a heartbeat

By weeks 8 to 10, you may feel like pregnancy symptoms are in full swing. Hormone levels are near their peak during this window, which means nausea and food aversions often reach their most intense point. As progesterone works its magic to support the pregnancy, you may notice continued breast tenderness, bloating, constipation, or heartburn as progesterone relaxes smooth muscle throughout the body. You may also find that your clothes feel a little tighter, even though the uterus is still relatively small—this is usually due to bloating rather than a visible baby bump just yet.

These few weeks are also so exciting because this is when many patients have their first prenatal visit and ultrasound, especially if they conceived without clinic support. On ultrasound, the embryo has grown dramatically since the early weeks and now clearly looks like a tiny developing baby. A heartbeat is usually visible, and your provider will often measure the embryo (called the crown–rump length) to help confirm the due date.

By the end of week 10, most of the major organs have begun forming, marking the end of the most critical period of embryonic development and the transition toward the next phase of pregnancy.

• Hormones are at their peak

• Bloating may be visible (not a baby bump, yet!)

• Pregnancy symptoms still increasing in intensity

• First doctor’s appointment and ultrasound

• Size: 14 to 20 mm 

• The most critical period of embryonic development is finishing up

• Major organs have begun forming