Quick answer
The first trimester runs from week 1 through week 13. Take a daily prenatal vitamin with at least 400 micrograms of folic acid, eat protein and iron at most meals, drink water, and let go of any food your stomach is rejecting today. According to ACOG, you usually do not need extra calories in this stretch. Most people gain 1 to 5 pounds, and many gain nothing at all. That is normal. Nausea, exhaustion, and food aversions are also normal and tend to peak around week 9. Symptoms typically ease between weeks 12 and 14. Severe vomiting that prevents you from keeping liquids down, heavy bleeding, or one-sided abdominal pain are not normal and warrant a same-day call to your obstetric provider. Below, we walk through what is happening week by week, the foods that help, the ones to skip, and the symptoms that warrant a same-day call to your provider rather than waiting.
What's happening: weeks 1 through 13
The first trimester is the loudest construction site of the whole pregnancy. Almost every major organ in your baby starts forming in these 13 weeks, and your body throws the kitchen sink of hormones at the project. That is why you can feel exhausted, queasy, and weirdly emotional all in the same afternoon. None of that means something is wrong. It means the project is on schedule.
Here is a rough map. Dating runs from the first day of your last period, which means weeks 1 and 2 happen before conception. That is not a typo, just an old convention obstetrics still uses.
- Weeks 1 to 4. Implantation. The fertilized egg burrows into the uterine lining. Many people do not yet know they are pregnant. A missed period is usually the first hint.
- Weeks 5 to 6. The neural tube starts closing. This is the structure that becomes the brain and spinal cord. Folic acid matters most in this window, which is why ACOG recommends starting a prenatal with at least 400 micrograms of folic acid before pregnancy when possible.
- Weeks 7 to 8. The heart begins beating in a steady pattern. Many people get their first ultrasound. Morning sickness often kicks in and tends to peak around week 9.
- Week 9. Tiny limbs, tiny features. Aversions are often at their loudest this week. The food you adored last month may suddenly read as disgusting.
- Weeks 10 to 11. Many people describe a brief easier stretch right around here, sometimes called the calm window. We will come back to it.
- Weeks 12 to 13. Risk of miscarriage drops noticeably for most pregnancies, and energy often begins to return at the end of week 13 or into early second trimester.
If your weeks do not match this neat list, that is also fine. Symptoms vary wildly between people and between pregnancies. The list is a map, not a deadline.
Foods that help in the first trimester
You do not need a complicated meal plan. The five priorities are protein, iron, folate, choline, and omega-3. If most of your meals hit two or three of these, you are doing well.
Protein
Protein supports tissue growth and helps keep blood sugar stable, which can take some of the edge off nausea. Aim for protein at every meal when you can. Easy options include eggs, Greek yogurt, cottage cheese, lentils, chickpeas, tofu, chicken, and lower-mercury fish. If meat smells repulsive, lean on dairy and legumes. If dairy turns on you, lean on eggs and beans.
Iron
According to the NIH Office of Dietary Supplements, the recommended daily iron intake during pregnancy is 27 milligrams, almost double the non-pregnant amount. It supports the extra blood volume your body is building. Sources include lean beef, lentils, chickpeas, tofu, spinach, pumpkin seeds, and fortified cereals. Pair plant-based iron with vitamin C to improve absorption. If iron from prenatals upsets your stomach, take it with a small snack.
Folate and folic acid
Folate (food) and folic acid (supplements, fortified grains) both help prevent neural tube defects in the early weeks. ACOG recommends at least 400 micrograms daily, ideally starting one month before conception and through the first 12 weeks. Food sources include leafy greens, lentils, asparagus, oranges, avocado, and fortified bread. Most prenatals cover the supplemental dose.
Choline
Choline supports fetal brain development. NIH ODS sets the adequate intake at 450 mg per day during pregnancy. Whole eggs are the most reliable source (about 147 mg per large egg). Beef, chicken, fish, soybeans, and cottage cheese contribute. Our choline deep-dive goes further.
Omega-3 fatty acids
Omega-3s, especially DHA, support fetal brain and eye development. The FDA and EPA advise 8 to 12 ounces of lower-mercury fish per week during pregnancy. Salmon, sardines, anchovies, trout, and tilapia are on the Best Choices list. If fish is not happening, walnuts, chia, flaxseed, or an algae DHA supplement are reasonable bridges. Ask your doctor before starting supplements.
Foods to avoid in the first trimester
The avoid list comes down to two risks: bacterial contamination, especially listeria, and toxin exposure like methylmercury or alcohol.
Listeria risk. According to the CDC, pregnant women are about 10 times more likely to get a listeria infection than the general population. About one in four pregnant women who get listeriosis lose their pregnancy or their newborn shortly after birth. That is why the avoid list is strict around foods that have caused outbreaks.
- Unpasteurized dairy. Skip raw-milk cheese and any product whose label does not say pasteurized. Most US and UK supermarket dairy is pasteurized by default.
- Soft cheese with mold rinds. The NHS advises avoiding soft mold-ripened cheeses (brie, camembert, chèvre) and soft blues (roquefort, gorgonzola) unless cooked until steaming. Hard cheeses (cheddar, parmesan) are fine. Cottage cheese, ricotta, and cream cheese are fine when pasteurized. More on cottage cheese.
- Deli meats and pâté. Cold cuts have caused listeria outbreaks. Heat them until steaming. Avoid liver-based pâté entirely (also high in vitamin A). Full deli meat guide.
- Raw or undercooked fish, shellfish, eggs, and meat. Skip raw-fish sushi, raw oysters, runny eggs from non-pasteurized sources, and rare steak. Cooked sushi rolls and fully cooked eggs are fine.
- High-mercury fish. The FDA says to avoid shark, swordfish, king mackerel, tilefish, marlin, orange roughy, and bigeye tuna. Canned light tuna is fine in moderation.
- Alcohol. No amount is shown to be safe during pregnancy. Skip it entirely.
- Excess caffeine. ACOG's committee opinion sets the ceiling at less than 200 mg per day, about one 12-ounce cup of brewed coffee. Tea, soda, energy drinks, and chocolate count.
- Liver. NHS recommends avoiding liver and liver products. The vitamin A content can be high enough to harm fetal development.
- Some herbal teas. NHS advises caution with herbal teas in the first trimester. Ginger, peppermint, and rooibos in modest amounts are commonly considered safer choices. Ask your provider about anything else.
For the highly processed end of the food spectrum, see our piece on ultra-processed foods and pregnancy.
Morning sickness reality
Morning sickness is misnamed. It can hit any time of day and turn favorite foods into enemies. According to ACOG, roughly 70 percent of pregnant people experience nausea and vomiting, usually starting around week 6 and easing by week 14. The hormonal driver is hCG, which peaks around week 9 to 10 and drops after.
What tends to help, in plain terms.
- Eat small, eat often. An empty stomach makes nausea worse. Bland carbs like crackers, toast, rice, and oatmeal are usually tolerated.
- Protein at the bedside. A handful of nuts or a few crackers with cheese before getting out of bed can blunt morning queasiness.
- Cold over hot. Cold foods give off less smell. Yogurt, fruit, smoothies, sandwiches, and cold pasta salads tend to land better than hot, fragrant meals.
- Ginger. Ginger tea, ginger chews, and ginger ale with real ginger have evidence behind them for mild nausea.
- Hydrate in tiny sips. Water with lemon, electrolyte drinks, popsicles, or ice chips can help when full glasses do not stay down.
- Vitamin B6 and doxylamine. ACOG lists this combination as a first-line treatment when lifestyle changes are not enough. Discuss it with your provider before starting.
Food aversions are part of the same hormonal package. Smell sensitivity skyrockets, and brain regions that decide what tastes good get rewired temporarily. The aversion will pass. Do not force a food that turns your stomach. Switch to something neutral and try again in a few weeks.
When morning sickness needs medical attention
Most morning sickness is uncomfortable but safe. A small percentage develops into hyperemesis gravidarum, a severe form that ACOG notes affects up to 3 percent of pregnancies and usually requires medical treatment. ACOG defines a key warning sign as losing 5 percent of your prepregnancy weight along with signs of dehydration. Call your provider if you cannot keep down liquids for 24 hours, you are urinating very little or your urine is dark, you feel dizzy or faint when standing, you are losing weight, or you see blood when you vomit.
When to call your doctor
Most first-trimester discomfort is normal. A short list of symptoms is not, and any of them is a reason to call your obstetric provider the same day rather than wait for your next appointment.
Call your doctor if you have:
- Heavy vaginal bleeding, especially with cramping or pain.
- Severe one-sided abdominal pain, which can suggest ectopic pregnancy.
- Severe, persistent vomiting and any of the dehydration signs listed above.
- A fever over 100.4°F (38°C), especially with chills or back pain.
- Sudden, severe headaches, vision changes, or facial swelling.
- Painful urination, since untreated UTIs in pregnancy can escalate.
- Any food that you suspect was contaminated, especially deli meat, soft cheese, or raw seafood, followed by fever or flu-like symptoms within a few weeks.
If something feels wrong and is not on this list, call anyway. Your provider would rather hear from you twice for a false alarm than once too late.
Bonus: the calm window around weeks 9 to 11
Some pregnant people describe a short stretch in the late first trimester where everything quiets down. Nausea eases for a day or two. Energy creeps back. Food sounds appealing again. We sometimes call this the calm window, usually clustered around weeks 9, 10, and 11.
The biological hand-wave for it is that hCG starts to drop after its week 9 peak and the placenta is taking over hormone production. Some people get a clear easing. Others get a brief tease and then symptoms come back. Both are normal. The point of naming the calm window is not to promise it. It is to give you permission to eat well when it shows up. If week 10 feels good, that is a great moment to bank some protein, iron, and choline. Our week 10 deep-dive covers this in detail, including a sample plan for the days when food finally tastes like food.
A day on a plate
This is one example of an uncomplicated first-trimester day that hits the priority nutrients. Treat it as a starting point. Swap anything that turns your stomach today and come back to it next week.
- Before getting up. A handful of plain crackers and a sip of water on the bedside table.
- Breakfast. Two scrambled eggs on whole-grain toast, half an avocado, a few raspberries, and a small glass of orange juice. Decaf coffee or tea on the side if you want it.
- Mid-morning snack. Plain Greek yogurt with a spoonful of granola and a few sliced strawberries.
- Lunch. A bowl of lentil soup with a squeeze of lemon, a slice of cheddar on whole-grain bread, and a side salad with olive oil and lemon.
- Afternoon snack. Cottage cheese with sliced peach, or a small handful of walnuts and an apple if dairy is off today.
- Dinner. Baked salmon, roast sweet potato, and steamed broccoli with olive oil and salt. Or, on a no-fish day, a tofu and chickpea stir-fry over brown rice.
- Evening. A mug of caffeine-free ginger or rooibos tea. A small bowl of fruit if you are still hungry.
This sample day lands roughly in the right range for protein, iron, folate, choline, and omega-3, plus enough calcium and vitamin C to round things out. It is not a prescription. It is a shape your meals can settle into when energy allows. If today is a saltines-and-ginger-ale day instead, that is also fine. If you came to pregnancy after a glucose-affecting medication, our piece on nutrition after GLP-1 has tailored notes that may apply.
Frequently asked questions
How many extra calories do I need in the first trimester?
Usually none. According to ACOG, most people do not need extra calories in the first trimester and gain 1 to 5 pounds. Needs rise by about 340 calories a day in the second trimester, more in the third.
Is it normal to lose weight in the first trimester?
It can be, especially if morning sickness is significant. Small losses are common. Losing 5 percent or more of your prepregnancy weight, or losing weight with dehydration signs, is a reason to call your provider. ACOG flags that threshold for hyperemesis gravidarum.
Can I drink coffee in the first trimester?
Yes, in moderation. ACOG and NHS consider less than 200 mg per day a reasonable ceiling — about one 12-ounce cup of brewed coffee. Tea, soda, energy drinks, and chocolate count.
Do I need a prenatal vitamin if my diet is good?
Yes. Folic acid from food alone is hard to guarantee, especially in the early weeks before many people know they are pregnant. ACOG recommends a daily prenatal with at least 400 mcg of folic acid. Iron, iodine, and choline are also commonly under-consumed.
What if I cannot eat anything except crackers and ginger ale this week?
Eat the crackers and ginger ale. Sip electrolyte drinks if you can. The first-trimester nutrient gap is small and easy to close once your stomach settles. The bigger risk is dehydration. If you cannot keep liquids down for 24 hours, call your provider.
Is it safe to eat sushi during pregnancy?
Cooked sushi rolls are fine. Raw-fish sushi is on the avoid list because of bacterial and parasite risk. See our sushi during pregnancy trimester guide.
When does morning sickness usually end?
For most people, the worst eases between weeks 12 and 14. Some have symptoms longer. Treatment options exist if symptoms are severe.
This guide is editorial information and not a substitute for personalized medical advice. If you have specific concerns, ask your obstetric provider.