Pregnancy is divided into three main stages called trimesters, each lasting roughly 13 to 14 weeks across a full 40-week term. After the baby arrives, a recovery period sometimes called the “fourth trimester” rounds out the experience. Here’s what happens in your body and to the developing baby at each stage.
First Trimester: Weeks 1 Through 13
The first trimester runs from the first day of your last menstrual period through 13 weeks and 6 days. This is when all major organ systems begin to form. By about week 5 or 6, the heart starts beating. The brain, spinal cord, arms, legs, fingers, and toes all take shape during these early weeks. By the end of the first trimester, the developing baby is about 3 inches long and has a recognizable human form, even though it weighs less than an ounce.
For you, this trimester often feels the hardest relative to how little you’re showing. Nausea, fatigue, breast tenderness, and frequent urination are common. These symptoms are driven largely by a rapid surge in pregnancy hormones. Your blood plasma volume starts increasing as early as 6 to 8 weeks, which is one reason you may feel lightheaded or extra tired even though the baby is still tiny.
Most people schedule their first prenatal visit between weeks 8 and 10. The traditional prenatal schedule calls for appointments every 4 weeks through the first and second trimesters, though your provider may adjust this based on your health history.
Second Trimester: Weeks 14 Through 27
The second trimester spans week 14 through 27 weeks and 6 days, and many people consider it the most comfortable stretch. Nausea typically fades, energy returns, and the bump becomes visible. This is the period of rapid growth and development. The baby begins to move, and most people feel those first flutters (called quickening) somewhere between weeks 16 and 20. By week 22 or so, the baby can hear sounds from outside the womb.
Your cardiovascular system is working significantly harder now. By around 24 weeks, cardiac output (the amount of blood your heart pumps per minute) can increase by as much as 45% compared to before pregnancy. Plasma volume continues rising until about 28 to 30 weeks. These changes support the placenta and the baby’s increasing nutritional demands, but they can also cause swelling in your feet and hands, visible veins, and occasional dizziness.
A glucose screening test is typically done between 24 and 28 weeks to check for gestational diabetes. An anatomy scan, usually performed around week 20, gives a detailed look at the baby’s organs, spine, and limbs.
Third Trimester: Weeks 28 Through 40
The third trimester begins at 28 weeks and continues through delivery, usually around 40 weeks. The baby’s main job now is gaining weight and allowing organs to fully mature. The lungs are one of the last organs to finish developing, reaching full maturity between weeks 38 and 40. This is a key reason why babies born even a few weeks early can have breathing difficulties.
During the final weeks, the baby typically turns head-down in preparation for birth. By around week 36, the head may drop into the pelvic area, a process called lightening. You might notice it’s suddenly easier to breathe but harder to walk comfortably.
Prenatal visits become more frequent in the third trimester: every 2 weeks starting around week 28, then weekly from about week 36 until delivery. Your provider will monitor blood pressure, the baby’s position, and growth more closely during this period. Common symptoms include back pain, trouble sleeping, frequent urination (again), and Braxton Hicks contractions, which are practice contractions that feel like tightening across your belly.
Weight Gain Across All Three Trimesters
How much weight you gain depends on your pre-pregnancy body mass index. For overweight individuals (BMI 25 to 29.9), the recommended total gain is 15 to 25 pounds. For those with a BMI of 30 or higher, the recommendation is 11 to 20 pounds. If you’re carrying twins, the numbers are higher: 37 to 54 pounds for a normal-weight starting point, 31 to 50 pounds if overweight, and 25 to 42 pounds if obese.
Most of the weight gain happens in the second and third trimesters. In the first trimester, gaining 1 to 4 pounds total is typical. The weight includes the baby, placenta, amniotic fluid, increased blood volume, breast tissue, and fat stores your body builds to support breastfeeding.
The Stages of Labor and Birth
Labor itself has three distinct stages. The first stage is the longest and has two phases. During early labor, your cervix gradually opens to about 6 centimeters while contractions build in frequency and intensity. In active labor, the cervix dilates from 6 to 10 centimeters. Contractions become stronger, closer together, and more consistent.
The second stage is the actual birth. Once you’re fully dilated, you push with each contraction until the baby is delivered. This stage can last anywhere from a few minutes to a few hours, especially in a first pregnancy.
The third stage is delivery of the placenta. Mild contractions continue after the baby is born, helping move the placenta out. You push gently one more time, and it’s usually delivered within 5 to 30 minutes. Afterward, your uterus keeps contracting to shrink back toward its normal size and reduce bleeding.
The Fourth Trimester: Postpartum Recovery
The postpartum period, often called the fourth trimester, covers roughly the first 6 to 8 weeks after delivery. It unfolds in phases. The acute phase is the first 6 to 12 hours, when your body is adjusting most rapidly. The subacute phase lasts from about 24 hours after birth through 2 to 6 weeks, during which most of the visible healing takes place. A delayed phase extends from 6 weeks to about 6 months postpartum.
During these weeks, your uterus gradually shrinks back to its pre-pregnancy size, a process that takes up to 6 weeks. Vaginal bleeding (called lochia) can last just as long, starting heavy and tapering over time. Breast engorgement, sweating, constipation, and soreness in the perineal area are all common. If you had a cesarean section, the surface incision typically heals within about 10 days, but the deeper tissue layers can take up to 12 weeks. Hair loss, which can feel alarming, is a normal hormonal shift and usually resolves on its own within several months.
Recovery during this period is not just physical. Hormones shift dramatically after delivery, and sleep deprivation compounds everything. This is the stage where having a support system and a plan for rest makes the biggest practical difference.