Pregnancy Week Calculator

Pregnancy unfolds week by week with remarkable developmental milestones, distinct symptoms, and physical changes throughout the 40-week journey. Understanding what happens each week helps you appreciate your baby's growth, recognize normal versus concerning symptoms, and prepare for the changes ahead. While every pregnancy progresses uniquely, knowing typical weekly developments provides reassurance and helpful context.

Third Trimester Growth and Preparation

Week 28 begins the third trimester. The fetus weighs about 2.5 pounds and measures 14-15 inches. Lung development accelerates, though lungs aren't fully mature. The fetus can see light through your abdominal wall. Movement becomes stronger and sometimes uncomfortable.

By week 30, the fetus weighs approximately 3 pounds and measures 16 inches. Fat deposits increase, smoothing skin appearance and helping with temperature regulation after birth. The fetus practices breathing movements regularly. You might notice your belly moving visibly with kicks.

Week 32 brings continued weight gain to about 4 pounds and 17 inches. The fetus takes less dramatic positions as space becomes tighter. Bones are fully formed but still soft and flexible to ease delivery. Most fetuses have settled into head-down position, though some won't turn until closer to delivery.

At week 34, the fetus weighs about 5 pounds and measures 18 inches. Vernix thickens, and lanugo begins shedding. The fetus is practicing important skills like blinking, grasping, and breathing. If born now, outcomes are generally excellent with brief NICU stays.

Week 36 marks early term. The fetus weighs about 6 pounds and measures 18-19 inches. Lungs are nearly mature. The fetus is gaining about 0.5 pounds weekly now. Your belly has likely "dropped" as the baby settles lower into the pelvis, called lightening. Breathing becomes easier, but pelvic pressure increases.

By week 38, the fetus is full term, weighing 6.5-7 pounds and measuring 19-20 inches. All organ systems are mature. The fetus sheds more lanugo and vernix, though some might remain at birth. Movement might feel different—less kicking, more rolling and stretching—due to limited space.

Weeks 39-40 represent optimal delivery timing. The fetus weighs 7-8 pounds and measures 19-21 inches. Brain development continues rapidly. Fat continues accumulating for temperature regulation. You might experience nesting instincts and increased energy despite physical discomfort.

Prenatal Appointments and Testing

First trimester appointments establish pregnancy, confirm due date via ultrasound, and include initial bloodwork testing blood type, Rh factor, anemia, infections, and antibody screening. Genetic screening options are discussed, including first trimester combined screening and non-invasive prenatal testing (NIPT).

The 20-week anatomy scan represents the second trimester's most detailed ultrasound, examining fetal development, measuring growth, checking organ formation, and assessing placental position. Many parents learn the baby's sex during this scan if desired.

Third trimester appointments increase in frequency—bi-weekly from 28-36 weeks, then weekly until delivery. Each visit includes weight check, blood pressure monitoring, urine testing, fundal height measurement, and fetal heart rate assessment. Group B Strep screening occurs around week 36.

Preparing for Each Phase

First trimester preparation includes starting prenatal vitamins with folic acid, scheduling your first prenatal appointment, researching healthcare providers and delivery locations, and making early lifestyle adjustments like avoiding alcohol and raw foods.

Second trimester tasks include scheduling the anatomy scan, beginning childbirth class research, starting to think about nursery planning, and making pregnancy announcements after the first trimester if desired. This is an ideal time for babymoons or travel before third trimester restrictions.

Third trimester preparation intensifies: attend childbirth classes, tour your delivery hospital, install car seats, pack hospital bags by week 36, finalize nursery setup, stock basic baby supplies, and prepare siblings if applicable. Review labor signs and your provider's protocol for when to call.

Understanding week-by-week pregnancy progression helps you appreciate the remarkable development occurring inside you and recognize what changes and symptoms to expect at each stage, empowering informed decision-making and reducing anxiety about this transformative journey.

First Trimester Weekly Highlights

Weeks 1-4 encompass your last menstrual period, ovulation, conception, and implantation, though you won't know you're pregnant until week 4 or later. By week 4, the blastocyst has implanted in your uterine lining and begins producing hCG, the hormone that triggers positive pregnancy tests. The embryo consists of two layers that will develop into all body systems.

Week 5 brings rapid embryonic development. The neural tube, which becomes the brain and spinal cord, begins forming. The heart starts developing, though it's not yet beating. Many women first suspect pregnancy this week when their expected period doesn't arrive. Early symptoms like breast tenderness and fatigue might appear.

By week 6, the heart begins beating at approximately 110 beats per minute, detectable via transvaginal ultrasound though not yet visible on external monitors. The embryo measures about 0.25 inches (size of a lentil). Arm and leg buds appear. Morning sickness often begins this week as hCG levels rise rapidly.

Week 7 marks continued brain development and facial feature formation. Eyes, nostrils, and mouth begin taking shape. The embryo has a small tail that will disappear. Measuring about 0.5 inches, your baby is now the size of a blueberry. Food aversions and heightened sense of smell often emerge.

At week 8, all major organs have begun developing, and the embryo officially becomes a fetus. Fingers and toes are forming, though still webbed. The fetus makes spontaneous movements, though you can't feel them yet. Measuring about 0.6 inches (raspberry-sized), it's growing approximately one millimeter daily.

Week 9 brings continued rapid growth to about one inch long. The tail has disappeared completely. Basic facial features are present, with eyes fully formed but eyelids fused shut. External genitalia begin developing, though sex isn't yet visible on ultrasound. Morning sickness typically peaks this week.

By week 10, all vital organs are formed and beginning to function. Fingernails and hair start developing. The fetus can make small movements like bringing hands to face. Measuring about 1.25 inches (size of a strawberry), the fetus has completed the most critical developmental period. Miscarriage risk drops significantly after this week.

Weeks 11-12 mark the end of the first trimester. The fetus measures 2-2.5 inches and weighs about 0.5 ounces. Facial features become more defined, and the fetus can yawn and stretch. First prenatal screening tests often occur now. Many women notice improved energy as the second trimester approaches, though morning sickness might persist.

Warning Signs at Different Stages

First trimester red flags include heavy bleeding with cramping, severe abdominal pain, dizziness or fainting, and persistent vomiting preventing adequate hydration. These might indicate miscarriage, ectopic pregnancy, or hyperemesis gravidarum.

Second trimester warning signs include vaginal bleeding, severe abdominal pain, sudden swelling of hands and face, severe persistent headaches with vision changes, and absence of fetal movement after you've felt movement previously. Contact your provider immediately with these symptoms.

Third trimester concerns include decreased fetal movement, vaginal bleeding, fluid leaking, contractions before 37 weeks, severe headaches with vision changes or upper abdominal pain, and sudden severe swelling. These might indicate placental problems, preterm labor, or preeclampsia.

Second Trimester Weekly Development

Week 13 begins the second trimester. The fetus measures about 3 inches and weighs nearly one ounce. Vocal cords are forming. Your uterus has expanded enough that most women begin showing a visible baby bump. Energy typically improves, and morning sickness often subsides.

By week 14, the fetus can make facial expressions including squinting and frowning. Fine hair called lanugo begins covering the body, helping regulate temperature. Measuring 3.5 inches and weighing 1.5 ounces, the fetus is practicing breathing movements with amniotic fluid.

Week 16 brings continued growth to about 4.5 inches and 3.5 ounces. The nervous system is functioning, allowing coordinated limb movements. Some women begin feeling flutters of movement, though first-time mothers often don't notice until week 18-20. Your belly is clearly pregnant now.

At week 18, the fetus measures about 5.5 inches and weighs 7 ounces. Ears are positioned correctly and can hear muffled sounds including your heartbeat and voice. Fingerprints are forming. Many women notice definite movement this week, especially if it's not their first pregnancy.

Week 20 marks the halfway point and typically includes the detailed anatomy scan. The fetus measures about 6.5 inches crown to rump and weighs approximately 10 ounces. Sex is usually visible on ultrasound. Vernix, a protective coating, covers the skin. Movement becomes regular and unmistakable.

By week 22, the fetus weighs about 1 pound and measures 11 inches head to toe. Eyebrows and eyelashes are visible. The fetus practices grasping and can grasp the umbilical cord. You might notice patterns to movement and rest periods.

Week 24 marks viability—the point at which survival outside the womb becomes possible with intensive medical care, though significant complications are common. The fetus weighs about 1.3 pounds and measures 12 inches. Lungs are developing but not yet functional. Taste buds are forming.

Weeks 25-27 continue rapid brain development and weight gain. By week 27, the fetus weighs about 2 pounds and measures 14 inches. Eyes can open and close. The fetus responds to light, sound, and touch. You might notice hiccups—rhythmic jumping movements. The second trimester ends at week 27.

Maternal Changes Throughout Pregnancy

First trimester symptoms include extreme fatigue, morning sickness, frequent urination, breast tenderness, and food aversions. These result from rapidly rising hormone levels, particularly hCG, estrogen, and progesterone. Many women find this the hardest trimester despite minimal physical changes.

Second trimester often brings relief from early symptoms. Energy returns, morning sickness subsides, and many women describe this as the best phase. However, new symptoms emerge: round ligament pain, nasal congestion, bleeding gums, and possible heartburn. Your belly grows noticeably, and you'll need maternity clothes.

Third trimester physical discomforts intensify as the baby grows larger. Back pain, pelvic pressure, swelling in hands and feet, difficulty sleeping, heartburn, and Braxton Hicks contractions become common. Breathing can feel difficult as the uterus pushes upward against your diaphragm until lightening occurs.

Weight gain follows a typical pattern: 2-5 pounds total in the first trimester, then approximately 1 pound per week in the second and third trimesters. Total recommended gain ranges from 25-35 pounds for women with normal pre-pregnancy BMI, adjusted for underweight or overweight starting points.