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1st Trimester

Patient Education > How the Baby Develops

First Trimester Mother

(0 - 13 Weeks )

The First trimester of pregnancy lies between 0 to 13 weeks. Although women experience many of the same physical changes during this time, no two pregnancies are alike.

From a physiological standpoint, many body changes occur in the first three months, most of them invisible to the naked eye. But even if other people can’t tell that you’re pregnant, you’ll know for sure. You’ll feel “different” as your body starts its journey “prepping” for and “cocooning” that growing baby inside you.

First, there will be a surge in hormones associated with the pregnancy, affecting many organ systems including the uterus. Next, the uterus starts to change by growing and adapting to the pregnancy, although you will not perceive any growth in the stomach area for several months. If everything is normal, the cells will continue to grow and divide while the baby forms. Here are some other systemic and psychological changes you might experience.

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Increased Urine Output

This is a biggie, since it’s something you’ll notice right away. As the pregnancy progresses, the mother’s blood volume will expand. The kidneys will receive more blood flow and at a faster rate as the volume increases by about 50%. The increases in both blood volume and flow rate result in a better profusion of all the organ systems, especially the uterus. As the kidneys experience the increased blood volume at a faster rate, urine production is increased also. Translation for mothers: You’re going to have to go to the bathroom a lot. This blood flow and subsequent urine production is a gradual process that increases throughout the pregnancy.


Another change that you might notice is feeling as if you have a cold or are congested. This condition results from the mucus membranes becoming swollen and mucous production being more pronounced as the hormonal changes associated with pregnancy occur. Some women may think they have a cold and go to the doctor to get it checked out.

There is really not a whole lot you can do except to live with this condition. Taking nasal decongestants or antihistamines is not advisable since you don’t really have a cold, and you don’t want to take the unnecessary risk of hurting the fetus. Occasionally, symptoms may warrant the use of medications, but check with your doctor first. It varies how long this congestion lasts—it could last anywhere from a few weeks to the entire pregnancy. This isn’t usually a serious or debilitating problem that most women complain about—it’s just something to be noticed.

Morning Sickness

Morning sickness is probably the best-known symptom of early pregnancy

Anything can bring on morning sickness from a simple smell or odor from a food (or odors from perfume, trash, …you name it). Chances are that you might feel queasiness coming on after you taste a certain food or beverage. In my case, caffeine always did it for me—just the smell or taste of coffee or coke or any caffeine substance, and I felt the bile rising and the urge to up-chuck. The general rule of thumb in combating morning sickness is to
listen, really listen, to your body. If you feel you can’t eat a particular food, then focus primarily on hydration, in other words, push fluids into your body. And don’t eat until you feel better (with the obvious qualification that you have to eat something sometime).

just drink any liquids—focus on consuming more clear liquids rather than milk, for example. Some people can tolerate milk, but often it just worsens your nausea. You should know fairly quickly whether or not milk works for you. (Keep in mind that after the morning sickness goes away, which it should as the pregnancy progresses, you can add milk or other foods back into your diet.)

It’s not clear whether a diet high in proteins or complex carbohydrates helps with morning sickness. Eat as normally as possible, and “liberate” your food and liquid choices.


If you’re throwing up constantly, the doctor will rule out obvious causes first; for example if there is an inciting food or drug/medicine you’re taking that’s causing the vomiting. Keep in mind that vomiting isn’t always caused by pregnancy. You might simply have the flu or other viral infection, or some kind of gastro-intestinal disorder unrelated to pregnancy. In rare cases, vomiting may be caused by an abnormal pregnancy or other abnormal hormonal condition and should be checked out by the doctor. The doctor may prescribe an anti-emetic (antinausea) medicine for you; however, in general, most doctors will try nonprescription methods first because it’s less risky to the developing pregnancy. There are certain over-the-counter remedies that work occasionally, including ginger supplements.

If none of the above options work, the doctor may prescribe a prescription strength medication

Shortness of Breath

Some women complain about shortness of breath during the first trimester (or beyond). This condition could be caused either by hormonal changes or by the diaphragm being elevated due to the growing pregnancy so that it restricts the downward movement that allows a woman to expand her lungs. Sometimes, women may have a perception that they are having trouble breathing, but in fact, they are fine, and there is usually nothing about which to be concerned. If a shortness of breath occurs, the remedy is to stay calm and not panic. Take a few deep breaths and relax. Generally, that anxious feeling will pass, and your breathing will resume normally. However, if you have a prepregnancy pulmonary condition like asthma before becoming pregnant or develop it while you’re pregnant (which does happen), this condition could possibly be exacerbated with pregnancy, and you should consult your doctor immediately. Asthma is not something to fool around with at any time.

Get help quickly if you are an asthmatic. Check with your doctor to see which medicines you can use while pregnant.


There is a physiologic anemia that begins early in pregnancy and is considered normal. While it’s not really a true anemia in the classic sense—but rather a physiologic anemia, meaning that it only occurs in pregnancy—it still needs to be treated. What happens is that there is a 50% increase in an expectant mothers plasma volume, but only about a 20–40% increase in her red blood cells. This discrepancy leads to a dilutional effect. The body thinks it is anemic because of this dilutional effect, and the result is that the woman does actually feel tired. Because of this relative anemia.

However, rarely will a woman require more iron than can be found in the normal prenatal vitamin. Her anemic status will be checked again in the third trimester, and additional iron supplements may be added at that time as needed.

Other “Icky” Body Changes

Some other common symptoms or complaints during the first trimester are as follows:

Heartburn and indigestiongainor dizzinessand stressvaginal dischargediscomfort due to enlargementproblemschanges

Heartburn and Indigestion

In the case of heartburn or indigestion, conservative efforts are key. Before rushing to the doctor for medication, try to sort through the condition on your own. First, think about what you’re eating and avoid foods that give you heartburn, such as foods or drinks that have carbonation or rich sauces or juices that would increase gastric acid production. Also, don’t eat too close to bedtime or naptime. The recumbent position stimulates acid reflux and increases heartburn. Try a fairly bland diet for a while and drink lots of water.

Weight Gain

Some weight gain, particularly around the waist, is normal. However, if you’re gaining an inordinate amount of weight in the first trimester, consult with your doctor. First, make sure you are not pregnant with multiple gestations (i.e., twins). Next, try to rule out any physiological reason for the weight gain, such as any pre-existing medical condition or hormonal disorder (possibly thyroid disease, diabetes, or Cushing’s disease or syndrome). Make sure you’re eating a healthful diet with the requisite amounts of fruits, vegetables, proteins, and complex carbohydrates. Try to cut out excess sugar and calories, such as fried foods and fast foods. The first trimester is not the time to gain weight. An ideal weight gain for this period would likely be based on your body mass index (BMI), which can be calculated using your prepregnancy height and weight. These calculations can be performed at your doctor’s office, and at that time an estimate for an appropriate weight gain can be determined. However, for the average American woman, the ideal weight gain in the first half of pregnancy would be 5–7 pounds.

Here are two examples of BMI charts that health care providers use as a reference point. Of course, these charts are not for pregnant women, so you’ll have to figure out where you started prepregnancy and go from there


Constipation occurs because the intestines have less motility due to hormonal changes. What this means is that the intestines are not pushing the fecal matter through the bowel as efficiently as before the pregnancy. Therefore, the stools become drier as the water in them is reabsorbed by the intestines, which leads to firmer and drier stools, and the unpleasant feeling associated with constipation. The remedy is to drink lots of fluids (preferably water) and watch what you eat. Don’t eat a lot of cheese and greasy foods. If you can increase your fiber intake, so much the better. Try eating a good bran cereal in the morning and drink juice at that time as well. If these remedies don’t work, your doctor may need to prescribe a stool softener.


Backaches are pretty common in pregnancy. They are caused by the stress and strain on the muscles that support the lower back and pelvic region. There are also mechanical issues involved. As your center of gravity moves forward, you’ll lean backwards to compensate from flailing forward. Naturally, this creates an increased amount of strain on the back muscles. In addition, there are hormonal changes, specifically a hormone called relaxin, which is produced by the body and helps to loosen the ligaments and attachments in the pelvic region in order to accommodate the baby. All of these things, plus poor posture and possibly poor physical conditioning, can increase a person’s risk for back pain. The basic physiological change that is occurring is an inflammatory response to the strain-induced muscle and back injury. To relieve back pain, try some gentle stretching exercises in the morning and evening. Work on having good posture during the day and use a support pillow propped behind your lower back in an ergonomic chair if you are working at a desk. Take more frequent breaks to walk around and stretch—at least once an hour. If you have to lift something, make sure that you lift properly so you don’t aggravate the back problem. Don’t bend over; rather, squat down and lift with your legs and not your back.


Headaches can be pretty common in the first trimester, and often migraines are a problem for women who have had a pre-existing diagnosis . Again, conservative treatment is key. Identify the behavior that creates the headache if you can; for example, not enough sleep or not enough hydration, the wrong kinds of food, stress, or whatever. Try to alleviate the problem first. If that doesn’t work, you can consider taking Tylenol or using cold compresses on your forehead. If nothing seems to help, see your physician.

Faintness or Dizziness

During pregnancy, women can be more prone to a vagal reaction, which is a neurological reaction that dilates blood vessels leading to the brain and lowers the blood pressure temporarily causing a feeling of light-headedness. To combat feeling faint or dizzy, be careful about standing up too suddenly or making sudden changes in positions (from lying down to getting up too quickly). Again, make sure that you’re drinking plenty of fluids to offset this condition. Women who aren’t properly hydrated are more sensitive to this blood pressure drop.

Fatigue and Stress

Being tired is a common complaint that most pregnant women have, and it’s understandable. Because being pregnant is full of changes to your health, you should expect moments of fatigue and plan for them. Don’t expect your life to go on as it did before with the same degree of energy. Anticipate this exhausted condition because it will happen. By anticipating, you can better prepare yourself for the change and make some effort to make lifestyle changes to compensate for fatigue, such as adjusting your sleep and work schedule accordingly.

Stress isn’t good for you or the baby. Stress can cause all kinds of symptoms from headaches to anxiety to depression to affecting your immune system in a negative way. Stress also makes you more prone to infections (for example, colds, UTIs, and so on). There are two kinds of stress. One kind is productive—it’s the kind that motivates you to achieve goals or objectives, keeps you on time, and allows you to accomplish your tasks. This type of stress can be a good thing. But the other kind of stress is the kind that is defeating and keeps you from focusing and from achieving everything you need to do—it’s the opposite of the first type. This stress is counterproductive to your ability to manage affairs in your life or to maintain your health. These are the kinds of stressors that should be looked at more closely, and you should strive to reduce them and the situation that is causing the stress.

Increased Vaginal Discharge

An increased vaginal discharge is not unusual for pregnant women because it is caused by hormonal changes involving the cervix and vagina. In fact, women should expect to have more discharge coming from the vagina. In most cases, this is nothing that will pose a problem or interfere with your lifestyle, but vaginal discharge should not be confused with an infection. If you think you are having signs of an infection, for example, foul odor, pain, irritation, or bleeding, this could represent an infection, and you should see your doctor for an evaluation.

Breast Discomfort Due to Enlargement

Breast discomfort is pretty common among pregnant women as the breast stretches and enlarges in
order to accommodate future lactation. In fact, some women will suspect they are pregnant because their breasts hurt. Other women experience more discomfort closer to delivery. For many women, the pain varies from the beginning of the pregnancy until the end. It can feel like a brief, shooting pain or a dull ache. The most important thing you can do to alleviate the pain is to wear a good support bra and pay attention to any skin changes, like cracked nipples or irritated skin, which may require some form of treatment. Treatment is usually not necessary, but ointments can be prescribed that may help alleviate the symptoms. While most breast pain is fairly common and normal, it can also be an indicator of something being wrong with your breast (possibly an early tumor). Always tell your doctor if you are worried or the pain is out of the ordinary or unbearable.

Complexion Problems

Ever hear that a woman who is pregnant glows? In some cases, a woman’s complexion and skin actually look better during pregnancy, almost as if she is glowing. However, other women may develop a condition called chloasma (a darkening of the skin), which is also known as the “mask of pregnancy.” Basically, it’s a facial pigmentation caused by an increase in estrogen and progesterone. Also, those same hormonal changes can cause hyper pigmentation in other areas, for example, a line around the belly-button and darkening of the nipple area (areola) and perineum. Not to worry—usually these changes will fade after the delivery.

Venous (Vein) Changes

As pregnancy progresses, there is a decrease in vascular resistance, potentially relaxing the veins, which then can lead to a greater likelihood for hemorrhoids or varicose veins. There isn’t too much you can do about this, and it doesn’t affect everyone. If you’re having trouble with constipation, this can cause hemorrhoids. You can wear support hose for varicose veins, as long as they don’t go over the stomach. Consult your doctor if either condition becomes unbearable.

Emotional Changes

The emotional changes that occur in the first trimester can run the gamut from extreme happiness to extreme sadness, some of it depending on how you view your pregnancy. Don’t be surprised by this roller coaster of emotions—it’s natural with the hormonal changes that are occurring. Try to get plenty of sleep, since being tired can cause additional stress and more emotional upheaval. Surprisingly, some women have more energy during this time period, simply because they are happier. For the most part, however, women are less energetic because their body changes make them feel more tired. Remember that pregnancy does not solve any family problems you might have, and sometimes it can add to them. If you need to talk to someone, there are plenty of people available to help. You can look for support groups on the Internet or ask your doctor for references—and don’t forget your clergy if you’re so inclined. The important thing is to get help and not to try to tough it out alone.


As you’re changing and growing, so is the baby inside of you. It’s difficult to imagine just how much growth is packed into such a short period of time. In the first three months, the fetus is only 8–10 millimeters in length (the width of your thumb), but within that embryo is a beating heart with blood circulating through it and the potential for growth with the maturation of multiple organ systems. At this point, it’s difficult to determine the gender, but limb buds that will eventually change and become arms and legs are clearly visible. Doctors can also identify the cranial (head) portion of the fetus. They will use this crownrump length from an ultrasound (roughly the distance between the head portion of the embryo and its bottom side) as a form of measurement to determine how far along the pregnancy is. It’s actually fairly accurate when measured.

Physiological Changes in the Baby’s Growth

When the sperm meets the egg, a virtual explosion occurs in terms of rapid cellular division. By the end of the first trimester, most of the baby’s organ systems are formed, including the heart, lungs, kidneys, and digestive system. Still forming is the baby’s neurological system, including the brain, brain stem, and spinal cord. Organ formation occurs through most of the first trimester. Afterwards, the organ systems that have formed are increasing in size and maturation By about the fifth or sixth week of pregnancy, heart motion is visible with a trans-vaginal ultrasound, although most of the other systems are too small to see at this time. A fluid sac has developed around the fetus that will eventually comprise the amniotic fluid. The yolk sac is present in early pregnancy, although it slowly regresses and the placenta takes its place as the major support system of nutrients and the exchange of waste products.

The heart begins to beat

The head, arms, fingers, legs, and toes form

Major organs and the nervous system form

The placenta forms

Hair starts to grow

20 buds for future teeth appear

By the end of the first trimester, the foetus is about 4 inches long and weight just a bit more than 1 ounce.

1 Trimester Monitoring

First Month full physical examination, blood & urine tests.

Second Month weight, blood pressure and urine test for sugar & protein

Third Month Height, weight, foetal heartbeat, and uterus size

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