Pregnancy lasts about 40 weeks from the first day of your last menstrual period and is divided into three trimesters, each bringing distinct changes to your body and your developing baby. Whether you just found out you’re pregnant or you’re planning ahead, here’s a practical walkthrough of what to expect from detection through delivery.
Early Detection and Confirmation
If you have a typical 28-day menstrual cycle, a home pregnancy test can detect the pregnancy hormone hCG in your urine 12 to 15 days after ovulation. That lines up roughly with the day your period is due or just after. Testing too early is the most common reason for a false negative, so if you get a negative result but your period doesn’t come, wait a few days and test again. A blood test at your provider’s office can confirm the result and help establish how far along you are.
How Your Baby Develops
The first trimester (through about week 13) is when all major organs form. The heart begins beating, limb buds appear, and the brain and spinal cord take shape. Because so much foundational development happens in these early weeks, this is the period when the fetus is most vulnerable to harmful exposures.
The second trimester (weeks 14 through 27) is a stretch of rapid growth. You’ll likely start feeling movement somewhere between weeks 16 and 22. The fetus develops fingerprints, begins to hear sounds, and practices breathing movements using amniotic fluid.
During the third trimester (weeks 28 through 40), the baby gains significant weight and organs mature in preparation for life outside the womb. Bones harden between weeks 33 and 36, though the skull stays soft and flexible to allow passage through the birth canal.
Prenatal Vitamins and Nutrition
Folic acid is the single most important supplement to start early. The CDC recommends 400 micrograms daily for anyone who could become pregnant, ideally at least one month before conception. Folic acid dramatically reduces the risk of neural tube defects, which are serious birth defects of the brain and spine that develop in the first few weeks, often before you know you’re pregnant. Most prenatal vitamins contain 400 to 800 micrograms.
A standard prenatal vitamin also supplies iron (to support a nearly 50% increase in blood volume), calcium, and vitamin D. Your provider can recommend a specific formula based on your diet and health history. Eating a varied diet rich in whole grains, lean protein, fruits, and vegetables covers most other nutritional bases.
Foods to Avoid
Pregnant women are 10 times more likely than the general population to develop a Listeria infection, a bacterial illness that can cause miscarriage, stillbirth, or serious newborn illness. The foods most likely to carry Listeria include:
- Unheated deli meats, cold cuts, and hot dogs
- Soft cheeses made from unpasteurized milk (brie, camembert, blue-veined cheese, queso fresco)
- Refrigerated smoked seafood like lox or kippered fish (unless cooked into a dish)
- Unpasteurized milk and dairy products
- Raw or undercooked sprouts
Raw or undercooked fish and shellfish, including sushi and ceviche, also pose a risk. When it comes to cooked fish, avoid high-mercury species like shark, swordfish, king mackerel, and tilefish. Low-mercury options like shrimp, salmon, pollock, catfish, and canned light tuna are good choices and provide omega-3 fatty acids that support fetal brain development.
Screenings and Prenatal Visits
Your first prenatal visit typically happens between weeks 8 and 10 and includes blood work, a medical history review, and often an early ultrasound to confirm the due date. After that, visits are usually monthly through week 28, then every two weeks until week 36, then weekly until delivery.
Genetic screening options are offered in the first and second trimesters. A noninvasive prenatal test (NIPT) uses a blood draw to screen for chromosomal conditions like Down syndrome, usually around weeks 10 to 13. The nuchal translucency scan, an ultrasound measuring fluid at the back of the baby’s neck, is done in the same window. If an enlarged measurement or abnormality is found, you’ll be offered genetic counseling and diagnostic testing.
The anatomy scan, a detailed ultrasound examining the baby’s organs and structures, is performed between 18 and 22 weeks. This is the appointment where many parents learn the baby’s sex, but its primary purpose is checking the heart, brain, spine, kidneys, and limbs for structural issues.
Glucose screening for gestational diabetes happens between weeks 24 and 28. You’ll drink a sugary solution and have your blood drawn one hour later. A result below 140 mg/dL is considered normal. A result between 140 and 190 mg/dL means you’ll need a longer, three-hour follow-up test. A result of 190 mg/dL or higher indicates gestational diabetes. Some clinics use a lower cutoff of 130 mg/dL.
Weight Gain Guidelines
How much weight you should gain depends on your pre-pregnancy BMI. The CDC recommends the following ranges for a single baby:
- Underweight (BMI under 18.5): 28 to 40 pounds
- Normal weight (BMI 18.5 to 24.9): 25 to 35 pounds
- Overweight (BMI 25.0 to 29.9): 15 to 25 pounds
- Obese (BMI 30.0 to 39.9): 11 to 20 pounds
Most weight gain happens in the second and third trimesters. During the first trimester, gaining just 1 to 4 pounds total is typical. Gaining too much or too little can increase the risk of complications, so your provider will track your weight at each visit.
Exercise During Pregnancy
Current guidelines recommend at least 150 minutes of moderate-intensity aerobic activity per week, spread across multiple days. Walking, swimming, stationary cycling, and prenatal yoga all qualify. If you were already doing vigorous exercise before pregnancy, you can generally continue with your provider’s approval.
The old advice about keeping your heart rate under 140 beats per minute has been retired. A better gauge is the “talk test”: if you can carry on a conversation during exercise, you’re at an appropriate intensity. Activities to avoid include contact sports, anything with a high fall risk (skiing, horseback riding), and exercises done flat on your back after the first trimester, since the weight of the uterus can compress a major blood vessel.
Medications and Safety
Acetaminophen is considered the pain reliever of choice during pregnancy due to its long track record of safety. Ibuprofen and aspirin are generally avoided, especially after the first trimester. For allergy symptoms, first-generation antihistamines like chlorpheniramine have the best safety profile. Dextromethorphan, found in many cough suppressants, also appears safe.
Many prescription and over-the-counter medications have not been well studied in pregnancy. The safest approach is to check with your provider before starting or stopping anything, including herbal supplements.
Warning Signs to Watch For
Preeclampsia is one of the most serious pregnancy complications, involving dangerously high blood pressure that can damage organs. It typically develops after 20 weeks. Symptoms include swelling of the face or hands, a persistent headache that won’t respond to treatment, seeing spots or other vision changes, pain in the upper abdomen or shoulder, sudden weight gain, nausea and vomiting in the second half of pregnancy, and difficulty breathing. Severe cases involve blood pressure readings of 160/110 or higher. Preeclampsia requires immediate medical attention because it can progress quickly.
Other signs that warrant an urgent call to your provider include vaginal bleeding, a sudden gush or steady leak of fluid (which may signal your water breaking), a noticeable decrease in fetal movement, and severe or constant abdominal pain.
Mental Health During Pregnancy
Depression and anxiety during pregnancy are more common than many people realize, and they’re not a sign of weakness or a personal failing. ACOG recommends that providers screen for perinatal depression and anxiety at the first prenatal visit, again later in pregnancy, and at postpartum visits using standardized questionnaires. If your provider doesn’t bring it up, you can ask to be screened.
Hormonal shifts, sleep disruption, body changes, and life stress all contribute. Feeling persistently sad, anxious, or emotionally numb for more than two weeks is worth bringing up, because effective treatments exist and early support leads to better outcomes for both parent and baby.
Recognizing Labor
As your due date approaches, you may experience Braxton Hicks contractions, irregular tightening that comes and goes without a pattern. True labor contractions grow progressively stronger, longer, and closer together over time. A common guideline is to head to the hospital when contractions are about five minutes apart, last one minute each, and have followed that pattern for at least one hour.
Go to the hospital right away if your water breaks and contractions haven’t started, you’re bleeding heavily, you have constant severe pain with no relief between contractions, or you notice the baby is moving less than usual. When in doubt, call your provider. They would always rather hear from you than have you wait at home wondering.