The first trimester of pregnancy goes from the the first day of your last menstrual period (before baby is even conceived) through the end of the 13th week. Your body and your baby’s go through tremendous change in these three months!
Estimated reading time: 25 minutes
Let’s touch for a moment on your due date. The average length of pregnancy in a human is 280 days, or 40 weeks. The date is calculated from the first day of your last menstrual period. This means that your pregnancy is actually calculated from a point in your cycle that is before your little one was actually conceived. Remember that your due date is just an estimate, though. Only 4% of women deliver on their due dates, and 70% deliver within ten days of their due date. So rather than thinking of this as the day your baby will come, it’s mostly useful for giving you a general window of time – your baby will likely be born within two weeks before or after the due date (1).
This trimester started before your baby was even conceived, and at the time of conception, she was just two cells, invisible to the naked eye. The earliest a woman might know she is pregnant is usually week four. At that point, baby is a bundle of cells the size of a poppyseed, and doesn’t resemble a human baby. (Though already at that point, cells are starting to differentiate – there are distinct liver cells, blood cells, and neurons. (2).)
By the end of the thirteenth week, as you wrap up the first trimester, your little one is about the size of a peach and looks much more human. She has tiny fingers and toes and even the beginning of fingernails. She has a little face with mouth, nose, eyes, and ears. You can tell what sex he or she is if you could get a good look in person, but you’ll need to wait a few more weeks to be able to tell on ultrasound. Baby is even swallowing amniotic fluid and making breathing-like movements.
Let’s look at how much weight you should gain during pregnancy. In the first trimester of pregnancy, weight gain is typically about 1 to 5 pounds. As we mention in our Week 16 Pregnancy article, some women don’t actually gain at all during the first trimester or may even lose weight due to morning sickness. If this is the case for you, weight gain should pick up in the second trimester when your appetite returns and your baby’s growth accelerates.
Your doctor or midwife will talk to you about how much is advised for your specific situation, but here is a general guideline based on your prepregnancy weight:
Underweight (BMI less than 18.5) – gain 28 to 40 pounds
Normal weight (BMI 18.5 – 25) – gain 25 to 35 pounds
Overweight (BMI 26 – 29) – gain 15 to 25 pounds
Obese (BMI over 30) – gain 11 to 20 pounds
Learn More: How Much Weight to Gain During Pregnancy
You’ll likely finish the first trimester of your pregnancy with a tiny baby bump, small enough to camouflage if you’re not ready to tell the world just yet. And you may have had to give up your favorite jeans already. You may not need maternity clothes quite yet, but it’s probably a good time to start looking for things that can grow with you or scrutinizing your closet for things that are stretchy, flowy, or roomy in the midsection. Think about things you own with an oversized fit, dresses or tops with a high waist that will drape over your little bump, or switching out jeans and tees for leggings and tunics.
Your breasts may have grown as much as a full cup size, and they may be tender, sensitive, or sore. You may notice that your nipples get darker and larger and stick out more, and that the areolas get darker and larger. The number of milk glands increases in preparation for making milk and fat builds up in the breasts. A good supportive bra may help discomfort. Some people even like to sleep in a bra to avoid pain when the breasts move while rolling over or sitting up.
By the end of the first trimester of your pregnancy, the placenta is completely formed. The placenta is the lifeline between you and your baby. Your blood and baby’s don’t mix; the placenta absorbs nutrients, immune molecules, and oxygen molecules from your blood and passes these through the umbilical cord to your baby. Waste products from the baby pass through the umbilical cord to the placenta where they can pass into your blood to be eliminated by your kidneys and lungs (3). As if all of that isn’t enough, it also produces many of the different hormones that are essential in pregnancy, including estrogen, progesterone, and hCG.
In addition to delivering good things to your baby, the placenta helps to block things that could harm him. However, it isn’t able to filter out everything that could possibly harm him. So it’s still important that you make healthy decisions.
The amniotic sac, also called the membranes or bag of waters, surrounds your baby throughout pregnancy. It is made of a pair of membranes, the amnion and chorion, that are thin and transparent but tough. The amniotic fluid in the amniotic sac helps maintain an even temperature, provides for easy movement, and keeps your aby protected by absorbing outside bumps.
Hormones are chemicals that act as messengers that tell our bodies how to function. In pregnancy, especially the first trimester, there are huge shifts in hormones. This helps prepare the body, enable you to conceive, and maintain the pregnancy. (They also cause many of the uncomfortable symptoms we discuss below, but let’s talk about the good they do.) Some of the important hormones in early pregnancy include:
About 70 to 85% of pregnant women experience morning sickness. The cause is likely the hormone surges early in the first trimester of pregnancy (4). The nausea – with or without vomiting – is usually most intense in the morning, but may last all day. For most women, morning sickness resolves around the end of the first trimester. It hangs around longer for some women, but in those cases still usually subsides by week twenty. A few unfortunate souls may find that it persists throughout pregnancy. There’s no way to make it go away altogether, but there are some things you can do to try to minimize it:
Hyperemesis gravidarum is a more severe form of nausea and vomiting that occurs in around 2% of pregnancies. HG is diagnosed if a woman loses 5% of her prepregnancy weight and has other problems related to dehydration (5). It can result in hospitalization, IV fluids, or IV nutrition. Call your doctor if you can’t keep any food or fluids down for more than a day or are showing signs of dehydration: a small amount of urine or inability to urinate; dark-colored urine; the inability to keep down liquids; feeling dizzy or faint when you stand up; having a racing heartbeat.
One of the earliest symptoms some women experience during the first trimester of their pregnancy, and one that may persist throughout, is constipation. This means feeling like you need to have a bowel movement but are unable to, having painful bowel movements, and passing hard, dry stools. This may be caused by hormone shifts, particularly an increase in progesterone that relaxes muscles throughout your body and causes your bowels to slow down. Other factors include morning sickness that may cause dehydration (which leads to constipation) and the iron in prenatal vitamins.
There are some ways you can help to keep things moving better: fiber, found in fruits, vegetables, beans/legumes, and whole grains; drinking plenty of water; regular exercise; and even how you “go” matters – humans are designed to squat while eliminating which relaxes and straightens the muscles involved in passing stool. You can put your feet up on a stool while on the toilet, or use a product like Squatty Potty.
In early pregnancy, you may feel like you’re constantly running to the bathroom. Your kidneys are processing an increased volume of fluid, and your growing uterus also puts pressure on your bladder. There’s no magic trick to solving this problem. Don’t cut back on how much you drink; your body and your baby need you to stay hydrated. Just accept that frequent bathroom trips are a part of pregnancy. In the meantime, do your Kegels. Strengthening your pelvic floor muscles can help with the incontinence that may accompany frequent urination later in your pregnancy and after delivery.
Frequent urination is likely to improve in the second trimester. But it will return in your pregnancy’s third trimester, as your growing baby puts pressure on your bladder.
Fatigue catches some women off guard in early pregnancy. It’s easy to see why a person in her third trimester is tired. But it may be harder to see from the outside what’s going on in the body in early pregnancy. But fatigue may be among the first pregnancy symptoms noticed by many women. Even before you can see it, your body is working very hard! Your metabolism is running high even when you’re resting, your increased blood volume means that your heart beats faster and stronger, leading to faster pulse and breathing rates, and as with most symptoms, hormones play a factor.
It’s common for vaginal discharge to increase during pregnancy because of changes in the vagina and cervix. (If it’s bothersome to you, you can wear pantyliners to stay comfortable.) Normal discharge is sticky, clear, or white. If you notice any changes, like discharge that has changed color, has a bad odor, or comes with pain, itching, or soreness, call your doctor or midwife as it may signal a bacterial or yeast infection. These are easily treated, but don’t try to diagnose or treat yourself with over-the-counter medications.
Spotting is light vaginal bleeding. It may seem alarming, but it occurs in about 20% of women in the first trimester of pregnancy and doesn’t necessarily mean there’s a problem. It can be caused by increased blood supply to your pelvis, a tender cervix, new vascular connections as your uterus grows and placenta forms. Call your provider to check in about how to proceed. If it’s just a little spotting over a short period of time, they’ll likely tell you to rest, avoid sex for now, and not to exercise strenuously.
Bleeding is when you have vaginal bleeding that is as heavy as, or heavier than, a menstrual period. If you have heavy bleeding or bleeding abdominal pain, your provider might order an ultrasound or blood tests to determine what’s going on (3).
Many women experience food cravings and/or aversions during pregnancy. This is likely the results of a combination of factors: hormone changes; morning sickness that may make only certain foods palatable; increased sense of smell and taste; craving comfort foods during an emotional time; craving particular nutrients your body needs (though scientists haven’t been able to confirm a link.) If certain foods seem suddenly repulsive to you, it’s easy enough to avoid them. There is no single food that you have to eat; just focus on maintaining a nutrient-rich, balanced diet. As for cravings, just take care not to overindulge. It’s easier if you’re craving foods that are healthy. If you’re craving unhealthy foods, make sure they remain a once-in-a-while treat. Try substituting healthier things, like a baked potato instead of fries or a fruit smoothie in place of a milkshake.
If you happen to find yourself craving nonfood items, talk to your doctor. There is a condition called pica, where people have a desire to eat items that are not food. This condition is more common in pregnancy than in the non-pregnant population. While you may feel hesitant to talk about it, your doctors are familiar with it They will hold no judgment over it, and will help you manage it.
Learn more from the National Eating Disorders Association’s Pica information page.
Low blood pressure is common in the first two trimesters of pregnancy. Hormones cause your blood vessels to dilate to accommodate your increased blood volume which makes your blood pressure run lower. Things like dehydration and anemia that can be caused by morning sickness can also contribute to lower blood pressure. There typically isn’t any reason to worry about low blood pressure. It will likely rise in the third trimester. If not, it should return to normal after your baby is born. One thing to note is that low blood pressure can make you feel dizzy. If you find that that’s the case, you may find that these things help: don’t stand up too quickly; drink plenty of water; don’t take hot baths or showers (which aren’t recommended during pregnancy anyway); don’t stand for long periods of time, eat small meals throughout the day.
Some women enter pregnancy with high blood pressure, or hypertension. While this is usually of more concern later in pregnancy, your doctor will monitor it. You can manage it by choosing healthy foods, especially making sure to avoid those that are high in sodium, staying active by aiming for 30 minutes of activity each day, and trying to decrease the stress in your life. If these things aren’t helpful enough, your doctor can help you explore medication options. Most blood pressure medications are considered safe during pregnancy, but you should avoid ACE inhibitors. And never take anything without consulting your doctor or midwife.
Headaches are one of the most common symptoms that women experience during pregnancy, and they commonly appear in the first trimester. First trimester headaches may be due to hormone changes and an increase in blood volume (6). Another contributor may be morning sickness which can lead to low blood sugar and dehydration. And as early as the first trimester, you may experience nasal congestion (related to hormonal and blood volume changes) that can lead to sinus headaches.
To ease pregnancy headaches, make sure you stay hydrated, get enough rest, try shoulder circles and other tension-reducing exercises, take a warm bath or shower or use a hot pack on your shoulders or back of neck, try a cold compress on your forehead or back of neck, a warm compress over your nose and eyes. If none of these things work, talk to your doctor about using pain relievers on occasion. Most doctors agree that Tylenol is safe in pregnancy, but your doctor will know the specifics of your pregnancy, other meds you might take, other conditions, etc.
If you find that your mood is unpredictable and constantly shifting, don’t worry, you’re not alone, and you’re not just being dramatic. While it’s certainly relevant that you genuinely have every reason to be feeling excited, elated, stressed, overwhelmed, and so many other emotions, pregnancy mood swings are also largely affected by the huge hormone changes of the first trimester. These big changes in your hormones can affect the brain chemicals that regulate mood, called neurotransmitters. So if you’re not quite yourself, or feel like you’re on a roller coaster, take heart in knowing that it’s a normal part of pregnancy for many women.
Be gentle with yourself. You may feel best if you eat healthy foods and drink plenty of water, get enough sleep, get regular exercise, spend time in the sunshine, and make time for your hobbies or interests. None of these things are going to eliminate mood pregnancy’s mood swings, but they may make you feel your best as you ride it out.
Beyond the regular mood swings – fleeting emotions that come and go – some women experience excessive depression and/or anxiety in pregnancy. Again, this is absolutely normal. Some women feel guilty if they’re not 100% happy all the time when pregnant. But feeling sad or anxious does not mean that you’re not excited about your pregnancy or that you’re not feeling the way a pregnant woman “should.” Pregnancy brings huge life changes, and while they may feel exciting, they may also (even at the same time) feel overwhelming, scary, and stressful. You may worry about your health or that of your baby, about the financial impact of a new baby, about how your relationships will change, about what kind of parent you’ll be.
Not only are you not alone, you’d probably find that nearly every pregnant woman would tell you she’s had the same emotions. And even if you are struggling a bit more than it seems some other people might be, it’s still not uncommon. 20 – 25% of the overall population struggles with mental health challenges (most commonly, depression and/or anxiety), so it makes sense that you’d see similar numbers in the pregnant population. Perhaps even more, since it’s such a stressful time in your life. Talk to your doctor if you’re struggling. I assure you that they hear it often and won’t be surprised or put off by it.
Anemia, your body not having enough red blood cells or iron, is fairly common in pregnancy. This is because your blood volume increases, and your body needs more iron and vitamins to make more hemoglobin, which carries oxygen to the cells in your body. Less-than-optimal amounts of oxygen can affect your organs and tissues as well as your developing baby. Most cases of anemia in pregnancy are mild. But if you have more severe anemia, you’re at a greater risk for having a premature baby or one with low birth weight, or for the baby having anemia. Fortunately, anemia can be treated with an iron-rich diet, iron supplements, or IV infusions. But let your doctor know if you experience any anemia symptoms: tiredness or weakness, rapid heartbeat, shortness of breath, skin becoming pale, difficulty concentrating.
Pregnancy can cause a number of skin changes, thanks to the skin stretching and hormonal effects on things like melanin which produces pigment in your skin. Some of these things are more likely to occur later in your pregnancy, but some show up as early as the first trimester.
If you didn’t start taking a prenatal vitamin before you became pregnant, start one as soon as you learn that you’re expecting. Your nutritional needs increase in pregnancy to support your baby’s growth. While you should eat a healthy diet, doctors still recommend taking a daily prenatal vitamin on top of that to be sure you’re getting everything you need. Prenatal vitamins are made specifically for pregnant women and include important things like folic acid which helps protect your baby against birth defects of the spine and brain and iron which helps your body make the cells it needs to carry oxygen in your increased blood volume.
We recommend interviewing several doctors and/or midwives to find one who is the right fit for you. You may be able to do this in a short period of time, but it will likely take a little while and you will want to get a first prenatal appointment scheduled. So ask around or reach out to your gynecologist and get a first appointment on the books. You can always transfer care later if you decide to do so.
As we said, we recommend interviewing providers to make sure that you’re able to choose one whose birth philosophies and practices line up with what you want for your birth. This is a person you will see throughout your pregnancy, so you’ll need to feel comfortable with them, feel that they’ll support you in having the labor and birth that you desire, and feel confident in their medical expertise. If you want to have a natural childbirth, you’ll want to ask about how many of their clients attempt unmedicated birth, how they support those moms, how the hospital staff feels about the birth plans you make with your doctor, etc. You’ll also want to ask about things like policies on labor inductions, how they feel about laboring and delivering in various positions, how often they perform episiotomies, and what standard protocols are for IVs, fluids, and fetal monitoring during labor.
We have an article full of these questions and many more to help you with your interview process: Interview Questions to Ask OB GYN or Midwife
Of course you should always check with your doctor or midwife, but in a vast majority of pregnancies, exercise is not only safe but recommended. Exercise helps reduce back pain, constipation, bloating, and swelling, increase your energy, improve your mood, improve your posture, contributes to better sleep, decrease your risk of gestational diabetes, pre-eclampsia, and cesarean delivery (7). Aim for at least 30 minutes a day on most days. If you were active before pregnancy, your doctor will probably tell you that you can keep up your normal level of activity. If you weren’t active before, it’s still a good time to start, just be sure to increase gradually. A great place to start is with our Safe Core Exercises During Pregnancy post. Strengthening your core muscles now can help prevent things like back pain later.
You may not feel like eating all that much during the first trimester, and you probably won’t need any additional calories during this trimester, but make sure you’re choosing nutritious foods. Focus on protein (lean meats, fish, dairy, beans/legumes), whole grains, and plenty of fruits and vegetables in a variety of types and colors.
As we discuss in our Drinking Water During Pregnancy article, every chemical reaction that happens throughout your entire body require water. Your body is working so hard right now, and it needs plenty of water to keep everything running smoothly. Your body needs to stay hydrated in order to deliver nutrients to your baby, make blood cells and amniotic fluid, and to remove toxins and flush out waste from both you and baby. Drinking plenty of water can also help prevent headaches and ease nausea and constipation. Aim for eight to twelve glasses (or 64 to 96 ounces) of water each day.
It’s time to think about when you’ll tell family, friends, and your employer that you’re expecting. When you tell is absolutely up to you. Some people tell others as soon as they find out. Others like to wait until they’ve made it through the first trimester, so that the chances of miscarriage are lower. It’s really up to you when to tell, and there’s no right answer. It’s normal if you feel excited, nervous, scared, or ambivalent about telling others. There’s no right time to tell and no right way to tell.
If you work outside the home, it’s time to start having conversations about work. Talk about whether or not you’ll return to work after baby is born. If so, look into your employer’s maternity leave and start planning how long you’ll stay home. Also look into paternity leave, if available, or consider whether or not a partner, parent, or someone else will take any time off after baby is born.
Smoking, drinking alcohol, and any drug or medication not prescribed by your doctor during your pregnancy can harm your unborn baby.
Certain foods are more likely to carry bacteria and toxins that could make you and baby sick. These include raw sushi, cold cuts, raw eggs, unpasteurized dairy, and unwashed produce.
Hot tubs, saunas, hot baths and showers should be avoided as they can raise your body temperature too much. When your body temp raises, so does your baby’s, but his or her temp takes much longer to come down. The prolonged rise in temperature early in pregnancy can cause birth defects or miscarriage.
Scooping cat litter, as cat feces can carry a common parasite that can cause an infection called toxoplasmosis. If you are the only one available to scoop, wear gloves when you do so.
Gardening without gloves, for the same reason that you should wear them when scooping cat litter. Soil may contain the same parasite.
Spray painting, and it’s best to wear gloves and ventilate well if you’re doing any kind of painting.
There are many things that you may have heard you should avoid during pregnancy, but here are some that you don’t need to worry about as long as your own caregiver doesn’t caution against them
Read our First Prenatal Visit article for a more complete idea of what to expect at a first appointment, which usually happens between pregnancy week 6 and week 12. You should expect a nurse to check your vital signs and ask about your medical history. Expect to give a urine sample to check for excess protein or glucose in the urine and do a pregnancy test and have a vial or two of blood drawn to do a number of tests. If you’re at least ten weeks pregnant, they may check to see if they can hear a heartbeat, though they can’t always this early, so it’s no concern if not. The doctor or midwife will talk to you about how to have a safe and healthy pregnancy. He or she will do a pelvic exam, possibly with a pap smear.
Not all pregnant women will have an early ultrasound in the first trimester, but there are a variety of reasons why you might, including confirming a heartbeat, confirming dates, checking the location of the pregnancy (making sure it’s in the uterus, not ectopic), and looking for reasons behind pain or bleeding. An ultrasound may be transabdominal (scanning through the lower abdomen) or transvaginal (an internal probe that scans from inside the vagina.) Neither should cause pain or discomfort.
Your doctor may recommend or offer several different screenings that look for the possibility that your baby may have certain chromosomal conditions. (If the screenings show the possibility of an abnormality, follow-up tests can help confirm or rule out the diagnosis.) First trimester tests are typically NIPT (noninvasive prenatal screening) that is just a blood test, NT (nuchal translucency screening) which is an ultrasound, and if either of those show a high risk for certain congenital conditions, they can be followed up with a CVS (chorionic villus sampling) which takes a small sample of the placenta.
One of the things they’ll test in the first trimester of pregnancy is your Rhesus factor, or Rh factor. When you hear a person describe their blood type as A positive or B negative, for example, the words positive and negative refer to the presence of a tiny protein that’s sometimes found on red blood cells. Most people are positive, which creates no concern. The only possibility for a problem comes when mom is Rh negative and baby is Rh positive, which is called Rh incompatibility. Mom’s body may treat that unknown protein as a foreign material and attack it. But don’t worry – this is why they do the screenings. There’s a medication to treat Rh incompatibility. Learn more about the details of Rh factor, incompatibilities, and treatment in our What is Rhesus Factor article.
If you have any of the following symptoms, call your doctor or midwife right away:
Once you’ve made it to the end of your first trimester, be sure to check out Kopa Birth’s Second Trimester Pregnancy & Symptoms: The Ultimate Guide!
Kopa Birth’s online childbirth classes allow you to prepare for a natural childbirth from the comfort of your own home, 24/7. Enroll today in our free online childbirth class to learn more about preparing for a natural hospital birth.
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The first trimester of pregnancy goes from the the first day of your last menstrual period (before baby is even conceived) through the end of the 13th week. Your body
