Pregnancy lasts about 40 weeks from the first day of your last period, and each trimester brings a distinct set of physical changes, fetal milestones, and practical decisions. Whether you just got a positive test or you’re planning ahead, here’s a clear walkthrough of what happens to your body and your baby from start to finish.
First Trimester: Weeks 1 Through 13
The first trimester is when the most dramatic biological work happens, even though you may not look pregnant at all. After fertilization, the single cell divides rapidly as it travels through the fallopian tube and implants in the uterine lining. For the first eight weeks after fertilization, it’s called an embryo. From nine weeks on, it’s called a fetus.
During these early weeks, every major organ system begins to form. Cartilage for the limbs, hands, and feet appears (though it won’t harden into bone for a few more weeks). Eyelids form but stay sealed shut. The liver begins developing, the kidneys start producing urine, the pancreas begins making insulin, and fingernails take shape. Genitals also start to form, though they won’t be visible on an ultrasound for several more weeks.
What you’ll feel during all this construction is less miraculous and more miserable for many people. Nausea (with or without vomiting), extreme fatigue, breast tenderness, and frequent urination are the hallmarks. Your uterine lining thickens and its blood vessels enlarge to supply the embryo, which is part of why you may feel so drained. Some people sail through with minimal symptoms, while others struggle to keep food down for weeks. Both are normal.
Second Trimester: Weeks 14 Through 27
The second trimester is often called the most comfortable stretch of pregnancy. Nausea typically fades, energy returns, and the risk of miscarriage drops significantly. Your belly becomes visibly pregnant as the uterus rises above the pelvic bone, and your care team may start measuring fundal height, the distance from your pubic bone to the top of your uterus, to track growth.
The biggest milestone for most parents is feeling the baby move for the first time, sometimes called “quickening.” First-time mothers usually notice it between weeks 18 and 22, though it can be subtle at first, more like fluttering or bubbles than the dramatic kicks that come later. If you’ve been pregnant before, you may recognize the sensation a few weeks earlier.
New discomforts replace the old ones. Round ligament pain, a sharp or aching sensation on one or both sides of your lower belly, is common as the ligaments supporting your uterus stretch. Back pain, leg cramps, and nasal congestion also show up for many people. Your skin may darken along the midline of your abdomen or across the bridge of your nose.
Third Trimester: Weeks 28 Through 40
In the final trimester, your baby’s bones become fully formed and organs mature to the point where they can function independently. Weight gain accelerates for both you and the baby, and you’ll likely feel a dramatic increase in the strength and frequency of movement, including kicks, rolls, and hiccups.
Braxton Hicks contractions often appear during these months. They last about 30 seconds, come at irregular intervals, and aren’t painful, though they can be uncomfortable. They’re your uterus practicing, not a sign that labor has started. The difference between Braxton Hicks and real labor contractions is important to recognize:
- Braxton Hicks: Irregular, felt mainly in the front of your belly, and they don’t get closer together or stronger over time. They don’t open your cervix.
- True labor: Contractions are consistently stronger and closer together. Pain may radiate through your lower back, cervix, and entire body.
Other third-trimester realities include shortness of breath (the uterus pushes up against your diaphragm), heartburn, swollen feet and ankles, difficulty sleeping, and frequent bathroom trips as the baby’s head drops lower into your pelvis. Many people also experience a burst of energy and an urge to organize the house in the final weeks, commonly called “nesting.”
Prenatal Visits and Screening Tests
The traditional prenatal care model involves 12 to 14 in-person visits over the course of pregnancy. The standard rhythm is one appointment every four weeks until around the seventh month, every two weeks until the eighth month, and weekly from then until delivery. Your provider may adjust this schedule based on your individual risk factors and needs.
An initial comprehensive assessment is recommended before 10 weeks. This first visit covers your full medical and reproductive history and addresses factors that could affect your mental health and outcomes. At routine visits throughout pregnancy, your care team checks blood pressure, weight, and fundal height.
Key screening tests happen at specific windows. A glucose screening, which checks for gestational diabetes, is typically done between 24 and 28 weeks. If you have risk factors for diabetes or had gestational diabetes in a previous pregnancy, this test may be moved to the first trimester. Group B strep screening happens later in pregnancy, usually between weeks 35 and 37, with a simple vaginal and rectal swab. Early in pregnancy, blood work screens for blood type, anemia, infections, and immunity to certain diseases. Optional genetic screening, including blood tests and ultrasounds, can provide information about chromosomal conditions as early as the first trimester.
Foods and Drinks to Avoid
Pregnancy changes your immune system in ways that make you more vulnerable to certain foodborne illnesses. You are 10 times more likely to get a Listeria infection while pregnant, and Listeria can cause serious complications including miscarriage and stillbirth. The goal isn’t to overhaul your entire diet but to avoid the specific foods that carry the highest risk.
The main categories to skip or handle carefully:
- Deli meats and hot dogs: Avoid them unless heated until steaming. This includes cold cuts, fermented sausages, and refrigerated pâté or meat spreads.
- Soft and deli-sliced cheeses: Soft cheeses made from unpasteurized milk (brie, camembert, blue cheese, queso fresco) carry Listeria risk. Queso fresco-type cheeses are risky even when made from pasteurized milk. Cheese sliced at a deli counter is also best avoided unless heated.
- Raw or undercooked seafood, meat, and eggs: No sushi, sashimi, ceviche, rare steaks, or runny eggs. That also rules out homemade Caesar dressing, raw cookie dough, and homemade eggnog.
- High-mercury fish: Shark, swordfish, king mackerel, and tilefish accumulate enough mercury to affect fetal brain development.
- Unpasteurized drinks and dairy: Raw milk, raw juice, and raw cider can harbor harmful bacteria.
- Premade deli salads: Potato salad, chicken salad, tuna salad, egg salad, and coleslaw prepared at a deli are potential Listeria sources.
- Raw sprouts and unwashed produce: Alfalfa and bean sprouts are particularly risky. Wash all fruits and vegetables thoroughly, and don’t leave cut melon sitting out for more than two hours (one hour if the temperature is above 90°F).
- Raw flour: Unbaked dough and batter made with raw flour can carry harmful bacteria, separate from the egg risk.
Weight Gain Guidelines
How much weight you should gain depends on your pre-pregnancy BMI. In the second and third trimesters, if you started at a healthy weight, the general target is between half a pound and one pound per week. Your provider will give you a total range based on your starting point. People who begin pregnancy underweight are encouraged to gain more, while those who start at a higher weight have a narrower recommended range. Most of the weight isn’t body fat. It’s the baby, placenta, amniotic fluid, increased blood volume, larger uterus, and breast tissue.
True Labor vs. False Alarms
As your due date approaches, distinguishing real labor from Braxton Hicks becomes a practical skill. The simplest test is timing. True labor contractions form a pattern: they get longer, stronger, and closer together over time. Braxton Hicks contractions stay irregular and often stop entirely if you change positions, drink water, or rest.
Location also matters. Braxton Hicks tend to stay in the front of your belly. True labor pain often starts in the lower back and wraps around to the front, or you may feel it deep in your pelvis and cervix. If contractions are coming every five minutes, lasting about a minute each, and continuing for at least an hour, most providers consider that active enough to head to the hospital or birth center.