Pregnancy: What to Expect in Your First Trimester (Weeks 1-12)
Baby Size & Development by Week
Near the end of the first trimester (12 weeks gestation), your baby is nearly three inches long and weighs about one ounce. This is similar to the length of a peapod. Baby’s brain and spinal cord are developing rapidly.
Your baby is already active. They can squint, frown, open and shut their mouth, turn their head, make a fist and kick. You likely can’t feel these movements right now though.
In the womb, the placenta is formed and blood is circulating through the umbilical cord. Amniotic fluid cushions your baby and allows them to move around easily.
Baby's heartbeat can be heard as early as the twelfth week of pregnancy. The normal range for a baby's heart rate is 110–160 beats per minute. While some people believe heart rate can predict baby’s gender, it’s not a true indicator of whether baby is a girl or boy.
Learn more about the details of your baby's growth and development during weeks 1–12 below.
Weeks 1 through 6
Gestational age begins before fertilization and on the first day of your menstrual period. The first two weeks of your pregnancy are during your menstrual cycle. Next, during ovulation, a mature egg travels down your fallopian tube toward your uterus where it can be fertilized by sperm. Once fertilization occurs and a ball of cells implants into the uterine lining, an embryo is soon formed. Basic structures and organs begin to develop.
Baby is the size of a blueberry. The embryo, now half an inch long, has grown from a collection of developing blood vessels, vertebrae and internal organs (including a kidney that produces urine). The fingers are webbed and spread like a starfish. The toes have sprouted and feet taken shape. Facial features organize as the retinas, eyelids, palate and ear canals develop. In males, the penis begins to form. In girls, the clitoris and ovaries appear.
Baby is the size of a raspberry. The embryo measures 16 millimeters, about the size of a postage stamp. It looks more like a fetus, curled in a fetal position. The legs are extended, arms defined and elbows bent. The developing eyelids begin to close, external ears are forming, nostrils are defined and open and the upper lip is forming, too.
Baby is the size of a grape. The embryo measures 1.25 inches from crown to rump and weighs 1/30 of an ounce. Taste buds have developed, toes are separating, and the intestines move out of the umbilical cord and fully into the embryo's body. All the organs are in place and distinctly formed. Now, they must grow in size and become interconnected. As they do, the embryo becomes a fetus.
Baby is the size of a kumquat. With all organs in place, the fetus shifts its energy into growing over the next seven months until it’s a full-size, full-term infant. Tiny fingernails and toenails are growing, and hair follicles develop below the surface of the skin. The head is large and round, and the neck is visible beneath the tucked head. In males, the penis bud is clear. In females, genitalia start to show.
Baby is the size of a fig. Between weeks 9 and 12, baby doubles in size to three inches from head to toe. The connections between the nerves and muscles have tripled since last week. Teeth begin to take shape. About 70 grams of amniotic fluid bathe baby.
Baby is the size of a lime. At the end of the first trimester, baby weighs about 1/10 of an ounce. All major systems are in place, and organs are formed and functioning. Now, they begin the long, seven-month road to functioning outside the womb. Individuality is already present, as different babies have different facial expressions.
Baby is the size of a pea pod. All major organs have formed and will continue to develop. Bones are hardening, especially the long bones. The skin is thin and seethrough but will start to thicken soon.
Mother's Health: Pregnancy Changes in the First Trimester
The first trimester marks the beginning of subtle but significant changes in a woman’s body. From adjustments in hormone levels to big emotions and common twinges, here’s what to expect and when to call a doctor.
Bleeding and Cramping
Spotting and some cramping in early pregnancy can be common. The cervix is more vascular during pregnancy and can bleed easily after intercourse or a cervical exam. The uterus is also growing and changing to make room for your growing baby. As it grows, the uterus puts pressure on the surrounding ligaments and muscles.
When to call a doctor: All spotting in pregnancy should be discussed with your provider. Call your care team right away if cramping is severe and lasts more than an hour, there’s bleeding with the cramping or if you have nausea, vomiting, dizziness or faintness with increased pain and bleeding.
Backache, Hip or Pelvic Pain
Joints soften and loosen during pregnancy because of hormone changes. The growing baby changes the center of gravity and puts more pressure on your back.
At-home remedies for pregnancy back, hip or pelvic pain:
- Good posture
- Wear shoes with good support and low heels
- Wear a maternity or pelvic support belt
- Bend with your knees, not from your waist, when lifting something
- Avoid lifting heavy objects
- Lie down, apply ice or heat or take a warm bath for back pain
- Get a massage, if possible
- When getting up from a lying position, roll to your side before trying to sit or stand
- When standing in one place for a long time, place one foot on a low object, like a footstool
- Use the pelvic rock exercise: Sit, stand or kneel in a comfortable position, then breathe in and relax, breathe out and tighten your stomach muscles while pushing your belly button into your back as you curl your back outward — relax and repeat
When to call a doctor: Call your care team if the back pain is low and comes and goes regularly, or is high, under your ribs or near your waist on either side.
Your gums may become red, soft and more likely to bleed. Use a soft toothbrush, mild toothpaste and floss gently. See a dentist if your gums become painful or swollen. It’s a good idea to have your teeth and gums cleaned in a dentist’s office early in pregnancy, and again, before you have your baby.
Avoid being around people who are sick, wash your hands frequently, drink plenty of fluids and rest. Call your family provider if you have a fever higher than 100 degrees, a severe sore throat, chest pain or difficulty breathing.
At-home remedies for cold during pregnancy:
- Overall: Acetaminophen (Tylenol) in regular, extra strength and sinus variations as directed
- Runny nose: Antihistamines (Chlor-Trimeton 4mg, Claritin or Claritin D, Zyrtec, Benadryl) or Fluticasone (Flonase)
- Stuffy nose: Saline nasal spray, antihistamine
- Cough: Cough suppressants (Robitussin DM)
- Sore throat: Throat lozenges, benzocaine-menthol (Chloraseptic) spray
- Fever: Acetaminophen (Tylenol) as directed
Hormone changes slow down movement in the intestines. Prenatal vitamins and iron supplements may make it harder to have a bowel movement, too.
At-home remedies for constipation during pregnancy:
- Drink at least 8 glasses of water every day
- Eat plenty of fiber from fresh fruits, vegetables and whole grains
- Eat prunes or drink prune juice
- Avoid laxatives, instead, try a stool softener or fiber supplement
- Avoid straining with bowel movements
When to call a doctor: Call your care team if you experience severe abdominal pain or if you pass blood or mucus.
Pregnancy can be an emotional roller coaster for some women. Mood swings, irritability, irrational thoughts and tearfulness aren’t unusual. You may feel happy one minute and sad the next. It’s also common to feel disorganized and to have trouble concentrating.
These changes are due in part to hormonal changes, which occur especially during the first three months. Although there’s not a “cure” for these mood swings, you may feel better if you follow a healthy diet (avoid sugar, chocolate and caffeine, which can make you feel worse), get exercise, rest and talk about your feelings with your partner, family or friends. Women with a history of depression are more likely to struggle with depression during pregnancy.
Do expectant fathers experience emotional changes? Yes, expectant fathers can experience emotional changes that are common in pregnant women. These changes can be due to feeling pressure with their partner’s increased needs and emotional changes, having doubts about being a good father, being worried about the mother and baby’s health and finances. Many of these feelings are normal.
Symptoms of depression may include:
- Feelings of sadness or hopelessness
- Changes in appetite (not eating at all or eating too much)
- Difficulty falling asleep or sleeping too much
- Noticeable loss of interest or pleasure in almost all activities, constant tiredness
- Feelings of worthlessness
- Inability to concentrate, to remember or make decisions
When to call a doctor: If you’ve experienced some of these symptoms, and they’ve continued for longer than two weeks, speak to your provider, nurse or social worker for further evaluation. If you have thoughts about death, suicide or hurting yourself, call your provider, call 988 to be connected with a National Suicide Lifeline counselor or go to the emergency room immediately. It’s important to take proper care of depression during pregnancy. If you don’t, you may put your health at risk, which can harm both you and your baby.
Diarrhea can be caused by the flu, bacterial infections, certain foods and some medications. It’s characterized by more than one loose watery stool in a day.
At-home remedies for diarrhea during pregnancy:
- A BRAT diet which includes bananas, rice, applesauce and dry toast
- Use bismuth subsalicylate (Kaopectate) or loperamide (Imodium) following the directions on the package
When to call a doctor: Call your care team if your diarrhea lasts longer than a day.
Occasional dizziness is fairly common in pregnancy, especially if you sit or stand up too fast. Anemia or not drinking enough fluids can make it worse.
At-home remedies for dizziness during pregnancy:
- Move slowly when you change position
- If you feel dizzy, sit and put your head down or lie down
- Drink plenty of fluids
- Avoid standing in one place for too long without moving your legs
When to call a doctor: Call your healthcare provider if dizzy spells happen more than once a day or your heart races before you feel dizzy.
Fatigue is a natural occurrence in pregnancy. It results from hormonal, and other changes, in your body. Pregnancy places many demands on your body, and it’s normal to feel tired. It’s important to get both regular exercise and enough rest at night. Exercise helps you maintain a healthy weight and flexibility. It also stimulates circulation and fights fatigue and a depressed mood. It’s not unusual to find your energy returning as you move through the middle months of pregnancy.
Gas or Bloating
Pregnancy hormone changes cause everything to move slower through your intestines.
At-home remedies for gas or bloating during pregnancy:
- Avoid gas-forming foods, such as beans
- Spicy foods or carbonated beverages
- Rock in a rocking chair or lie on your left side
- Gas relief medication, like Mylicon, may be used
Groin or Round Ligament Pain
Early in pregnancy, all women have a small cyst on one of their ovaries that produces needed hormones for the pregnancy. There are also ligaments, or strong rubber-bandlike structures, that help hold your uterus in place as it grows. Either of these can cause a sharp, sudden pain on one side or the other of your lower abdomen. Both are harmless, even though they hurt.
At-home remedies for groin or round ligament pain during pregnancy:
- Move slowly when turning in bed
- Getting out of bed or a chair
- Avoid sudden, jerky movements
- Bend at the waist toward the side that hurts
- Massage or put heat on the area that hurts
- Run a warm bath
When to call a doctor: Call your care team if you have continuous pain lasting longer than two minutes in your lower abdomen or if you have weakness, headache, shoulder pain, nausea, dizziness, cramping or bleeding along with the pain.
Nasal congestion, fatigue, eyestrain, caffeine withdrawal, anxiety and tension are all possible causes of headaches. Rest and relaxation are often the most effective remedies for headaches. For headaches in the sinus area, press a hot, moist towel over your eyes and forehead. If nasal congestion is part of the problem, a humidifier or hot shower may help. If a headache persists or is accompanied by changes in vision, right upper quadrant pain, swelling in your hands or face, notify your provider immediately.
While pregnancy is not the time to have new glasses or contact lenses fitted, lenses that were fine before you became pregnant might cause a headache or strain now. Your body's increased volume of circulation during pregnancy can affect your vision, but these problems are only temporary.
Heartburn or Indigestion
Hormone changes of pregnancy allow the opening from the esophagus to the stomach to be more relaxed. As the baby grows, pressure on your stomach causes the acid to back up.
At-home remedies for heartburn or indigestion during pregnancy:
- Eat small amounts of food often
- Avoid overeating
- Don’t lie down right after eating, wait at least two hours
- Elevate your head at night or sleep in a semi-sitting position
- Avoid caffeine and cigarettes
- Avoid spicy and greasy foods
- Sip milk or eat yogurt
- Use antacids that are low in sodium
- Don’t use baking soda, Pepto Bismol or any product with aspirin in it
When to call a doctor: Call your care team if your heartburn isn’t relieved with antacids or these suggestions, or you get a frequent pain under your ribs on the right side.
Insomnia or Fatigue
Fatigue is common the first three months of your pregnancy and again toward the end of the pregnancy. It becomes harder to get comfortable as your baby grows. Back or hip pain or frequent trips to the bathroom often wake you up.
At-home remedies for insomnia or fatigue during pregnancy:
- A warm bath
- Relaxation exercise before sleep
- Exercise during the day but not within four hours of going to bed
- Have a light snack before you go to bed
- Sleep on your side with a pillow between your legs and under your abdomen
- Avoid caffeine
- Go to sleep and get up at the same time every day, whenever possible
- Use a pad over your mattress (like an “egg-crate” pad)
- Listen to your body and rest when you can
When to call a doctor: If you’re anxious or have many things on your mind, discuss them with someone close to you or consider seeing a mental health counselor. Call your care team if you continue to feel much more tired than usual and these suggestions don’t help.
The blood flow to your legs isn’t as good during pregnancy. Calcium imbalance, fatigue and prolonged standing or sitting can lead to more cramps.
At-home remedies for leg cramps during pregnancy:
- Drink plenty of water
- Get enough, but not too much calcium (about 4 servings of dairy products/day)
- Straighten your leg and point your toes toward your head to release cramps
- Use calf-stretching exercises (lean against a wall, hold one leg straight with the heel on the floor as you bend the other knee)
- Do foot twirls
- A magnesium supplement (e.g. Mag 64)
When to call a doctor: Call your care team if one leg is more swollen than the other, or if you have a painful, red area in your calf or other part of your leg.
Nausea and Vomiting (Morning Sickness)
Nausea and vomiting are common in the first three months of pregnancy due to hormone changes. Nausea may start between the fourth or ninth week but rarely continues beyond the end of the third month. Although it’s referred to as morning sickness, nausea and vomiting may occur at any time of the day.
At-home remedies for morning sickness during pregnancy:
- Eat frequent, small meals
- Divide your food into five small meals a day rather than three large ones, as keeping food in your stomach seems to control nausea
- Avoid greasy, spicy or rich foods that may disagree with you
- Try eating dry cereal, a piece of toast or a cracker about 30 minutes before getting out of bed in the morning, and move slowly when you get up
- Drink sips of fluid between meals, not with your meals
- Avoid strong smells
- Let plenty of fresh air into the house to get rid of odors
- Eat a high protein snack before bed to keep your blood sugar level
When to call a doctor: Listen to your body, do what seems to work for you. Call your care team if you can’t keep down food or fluids and become dehydrated or are losing weight.
Nosebleeds and Nasal Stuffiness
Increased blood flow to your nose causes mucus membranes to soften and swell during pregnancy. Dry air can also be a culprit. Don’t blow your nose vigorously, and only blow one nostril at a time. If you get a nosebleed, sit with your head resting on the back of a chair or recline slightly. Apply pressure to your nose by pinching the nose gently.
At-home remedies for nosebleeds and nasal stuffiness during pregnancy:
- A humidifier, if the air is dry
- Saline (salt) nasal sprays
- Lubricate each nostril with Vaseline on a Q-tip
- Nasal strips
When to call a doctor: Call your care team if nosebleeds are frequent, heavy or don’t stop within 30 minutes.
Shortness of Breath
Pregnancy hormone changes can cause you to feel the need to take deep breaths. This helps protect your baby by getting enough oxygen into your system. As your baby grows, pressure from the uterus may put pressure on your diaphragm, making it harder to breathe.
At-home remedies for shortness of breath during pregnancy:
- Use good posture
- Stand and sit straight
- Lift your rib cage or circle your shoulders up and back
- Avoid lying on your back
- Elevate your head on pillows when lying down
When to call a doctor: Call your care team if you have wheezing, trouble breathing, your heart is racing or you have chest pain along with feeling short of breath. Asthma may get worse with pregnancy. If you notice this, it’s very important to let your provider know.
During the first three months, your growing uterus takes up space your bladder normally has. Late in pregnancy, the baby’s head fills up that space.
At-home remedies for urinary frequency during pregnancy:
- Avoid drinking shortly before you go to bed
- Talk to your employer about more frequent bathroom breaks, if necessary
When to call a doctor: Call your care team if you have pain or burning with urination, a fever, backache near your waist or blood in your urine.
At-home remedies to help prevent vaginal infection and irritation during pregnancy:
- Wear cotton underwear
- Wipe from front to back after you go to the bathroom
- Avoid douching
- Avoid deodorized, scented or colored products
When to call a doctor: Call your care team if you notice a green, yellow or strong-smelling discharge or vaginal irritation or itching.
Varicose veins are swollen veins. They usually appear in the legs but can also appear in the vulva or vagina. Increased blood flow during pregnancy and pressure from your growing uterus slows the circulation in your legs. Hormone changes also cause the veins to relax. It’s more likely you’ll get varicose veins if others in your family have them.
At-home remedies to help limit or prevent varicose veins during pregnancy:
- Wear support stockings — put them on before you get out of bed
- Avoid tight bands from your stockings or anything else on your legs
- Elevate your legs and feet, ideally above your heart, when you can.
- Avoid long periods of sitting
When to call a doctor: Call your care team if you have a firm, red or tender area over one of your varicose veins, or one leg is more swollen than another.
Exercise & Diet During Pregnancy
Mild to moderate physical activity is beneficial to pregnant women and won’t harm the baby. Women who haven’t exercised regularly before becoming pregnant shouldn’t start a vigorous exercise program (high impact aerobics, cycling, jogging, etc.), but may do some low-impact exercises. Consider the following about regular exercise during pregnancy:
- If you have complications during your pregnancy, you may be advised not to exercise — talk to your provider about your special needs
- Begin and end exercise with a warmup and cool down
- Avoid exercising in hot weather
- Drink plenty of fluids
- Monitor your level of activity
- Moderate exercise is fine (walking, swimming, low impact aerobics, etc.)
- Avoid hard or extreme levels of activity
- Stop if you feel dizzy, faint, short of breath or have heavy cramping
Diet: Eat about 300 more calories than normal. Healthy foods, such as fresh fruits, vegetables, proteins and whole grains, are a great choice. Stay away from fast foods as they’re high in fats and salt. Limit your caffeine intake. Increase your calcium intake to 1500mg per day. Stay away from unpasteurized cheese and dairy (feta, goat cheese, blue cheese, etc.), undercooked meats and fish with high levels of mercury (shark, swordfish, tilefish, and king mackerel).
Take the recommended dose of a prenatal vitamin daily as early as possibly during, or before, your pregnancy. Talk to your OBGYN about vitamins and supplements you’re taking.
When to Call Your Provider in the First Trimester
If you experience any of the following, it’s best to call your healthcare provider to ensure you and baby are safe and healthy.
- Bleeding from your vagina
- Severe pain, cramps, or abdominal pressure that doesn’t go away
- Fainting or dizziness
- Severe headache or a headache that doesn’t go away with Tylenol or rest
- Sudden swelling in your hands, face, feet or ankles
- Rapid weight gain
- Blurred vision or spots in front of your eyes
- Pain or burning when you urinate
- Chills or fever above 100 degrees
- Severe nausea, vomiting, or diarrhea
- Rash or unusual sores on your body
- Discharge from your vagina that’s bloody, greenish, yellow, foul smelling, burning or itchy
- Leaking of clear fluid from your vagina
- Feeling consistently anxious, stress or depressed
As you navigate your first trimester, rest assured that our compassionate and knowledgeable care team is here to support you every step of the way. If you’re ever concerned about changes occurring in your body or have questions about your growing baby, always contact your care team.