For most women, the first 12 or so weeks of pregnancy are the most consuming because everything is new, exciting, and a bit overwhelming. Consider this your manual for understanding everything to come.

By Kate Neale Cooper

You're pregnant! Yay! Now let the questions about every little thing begin.

To satisfy the little voice inside your head (and hopefully put your mind at ease), we pulled together everything you can expect the first trimester. From definitions of the terms you're going to hear to the early pregnancy symptoms you're may experience, consider this your pregnancy primer. Keep it handy, and keep calm mama.

First Trimester Symptoms

Aversions (and Cravings)

Being repelled by certain tastes and smells is common. "Your digestion is slowing down, so some formerly appealing foods become intolerable," explains certified nurse-midwife Lisa Kane Low, Ph.D., R.N., a faculty member at the University of Michigan School of Medicine. Ignoring an aversion may only make you feel sicker, so don't feel you have to eat something just because you think it's good for you.

Cravings are the flip side of aversions: Although the cause is unknown, they may simply be your body's way of telling you to eat what you can stand. Unless they could be harmful (see "H"), go ahead and indulge them.


"Pregnant women always think of their bellies as the focal point," says Low, "but usually the first physical symptom they notice is a too-tight bra." In fact, the symptoms of early pregnancy, such as acne, mood swings, cramps and especially swollen, tender breasts, closely resemble PMS.

RELATEDBreast Changes Before and After Baby


Extreme fatigue is very common in the first trimester of pregnancy. "Your metabolic rate—the amount of energy you burn just to exist—is way above normal then," explains Low. The emotional ups and downs can also take their toll on you.

Fatigue should let up in your second trimester. But if it doesn't, you may be anemic—more than 50 percent of pregnant women are iron-deficient to some degree by week 28, according to Susan Watts, M.D., an obstetrician-gynecologist at Presbyterian Hospital of Dallas.

Weight Gain

While the average weight gain during the first trimester is about 5 pounds, some women actually lose weight because of morning sickness and food aversions. If it happens to you, don't panic: You'll soon see the numbers on the scale climb.

Just remember that pregnancy is not the time to go on a diet, but rather to eat as healthfully as you can (some women prefer eating six small meals throughout the day). "Anytime you deprive your body of the nutrients it needs, it has to rob them from someplace else," explains Low. That means invading emergency stores of calcium or iron, for example.

RELATEDTips for Healthy Pregnancy Weight Gain


Increased sensitivity to low blood sugar and higher levels of the hormones estrogen and Beta HCG can contribute to nausea. The following may help:

  • Eat something, anything—often: An empty stomach worsens nausea.
  • Sniff lemons or snack on lemon-flavored foods.
  • Drink at least eight glasses of water a day.
  • Try sports beverages, such as Gatorade. They also supply glucose and essential minerals.
  • Have a protein-rich bedtime snack. Protein keeps your stomach feeling full longer, making it easier to face the morning.
  • Wear acupressure wristbands, such as Sea-Bands (sold at most drugstores) or the prescription ReliefBand Device.
  • Move. Exercise diverts blood from your stomach, alleviating nausea.
  • Brush before eating. Toothbrushing stimulates the gag reflex.

First Trimester Tests

Pregnancy Tests

If you take a pregnancy test on the first day you miss your period, there's a 10 percent chance that you'll get a false negative reading, according to a report in the Journal of the American Medical Association. If you mistakenly believe that you are not pregnant, you might not avoid potentially harmful substances. In the interest of safety, assume (and act as if) you are pregnant and retest a week later.

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OB-GYN Appointments

Call your doctor for an appointment as soon as you believe you are pregnant. Some will want to see you right away, others not until you are eight weeks pregnant. Try to schedule prenatal visits so that your partner can come, too.


Most obstetricians will perform an ultrasound at your first prenatal visit to confirm your pregnancy and to date it if you don't know when you conceived. Later on, you'll probably have a transabdominal ultrasound (like the ones you see on TV), but the early exam may be performed by inserting a plastic wand into your vagina. (Don't worry—it doesn't hurt.)

RELATEDAll About Ultrasounds

Due Date

Pregnancy is based on a 40-week (280-day) calendar. To calculate your estimated date of delivery, add seven days to the first day of your last normal menstrual period, then add nine months. Your baby is considered full term if he arrives anywhere from three weeks before to two weeks after this date (more than 90 percent of babies do). If your menstrual cycle regularly is 28 days long, you're more likely to give birth near your due date.

If your cycle is usually longer than 28 days, you're more likely to deliver later; and if it's shorter, earlier. But the most accurate way to date a pregnancy is via ultrasound measurement of the fetus's crown-to-rump length between eight and 12 weeks.

Chorionic Villus Sampling (CVS) 

This diagnostic test for chromosomal disorders such as Down syndrome is usually performed between weeks 10 and 12. CVS can be done earlier than amniocentesis, but unlike amnio, it cannot detect neural-tube defects such as spina bifida.

In addition, says Donald R. Mattison, M.D., senior adviser to the directors of the National Institute of Child Health and Human Development and Center for Research for Mothers and Children, the miscarriage risk is slightly higher with CVS—around 1 percent vs. less than 1 percent for amnio.


First Trimester Health


Even before you conceive, start taking a prenatal multivitamin with 400 micrograms of folic acid daily (take 600 micrograms when you get pregnant). "Folic acid goes a long way toward preventing serious neural-tube defects of the brain and spinal cord," explains Mattison. Spina bifida is perhaps the most well-known of these problems.

Avoid over-the-counter prenatal vitamins that contain herbals or "natural" products; they are not as strictly regulated. If the vitamins upset your stomach, iron is probably the culprit. Ask your doctor about taking folic acid alone until your morning sickness passes. In the meantime, eat lots of folate- and iron-rich foods, such as beans, spinach and raisins.

RELATEDThe Benefits of Folic Acid

X and Y Chromosomes

The sperm determines the baby's sex. Here's how it works: The egg and sperm each contribute one chromosome. The egg always carries an X; the sperm, either an X or a Y. If the fertilizing sperm contains an X chromosome, you will have a girl. If it contains a Y, you're having a boy.


The fertilized egg, also known as a zygote, is the size of an apple seed when you can confirm that you're pregnant—about two weeks after conception. By week five, it's known as an embryo, and the placenta and umbilical cord are functioning. At eight or nine weeks, it's officially a fetus and all its organs have been formed.

By the end of the first trimester, it'll be almost 3 inches long and the face will look recognizably human. No wonder you're tired!

Genetic Counseling 

If you're at risk for having a baby with an inherited disorder, counseling can help you and your partner decide whether to undergo tests to determine if either of you is a carrier or to see if your fetus is affected. Age and personal and family medical histories are just a few factors to consider when deciding on testing.

RELATEDHealth 101: Genetic Testing Before & During Pregnancy


You may be surprised—and concerned—if your doctor prescribes antibiotics to treat a condition such as a simple gum or bladder infection. But infection anywhere in the body may lead to preterm labor. If your obstetrician prescribes antibiotics, it's likely because the benefits outweigh the risks. If another physician prescribes them, get your OB's approval before taking them.


Fifteen to 20 percent of all pregnancies end in miscarriage, usually in the first trimester. Many women blame themselves when it happens, but there is no evidence that emotional stress, physical activity or sex causes it. If you begin spotting, bleeding or cramping, call your doctor right away.

If you do miscarry and need help coping, ask your doctor to recommend a support group or find one online. Helpful books include Empty Cradle, Broken Heart: Surviving the Death of Your Baby by Deborah L. Davis, Ph.D. (Fulcrum, 1999); and Trying Again: A Guide to Pregnancy After Miscarriage, Stillbirth and Infant Loss by Ann Douglas and John R. Sussman, M.D. (Taylor, 2000).

RELATEDMiscarriage: Causes, Signs, and What to Expect

First Trimester Life Changes


There are a lot of reasons to get (or stay) physical in the first trimester. "Exercise may help alleviate nausea," says Renee Jeffreys, an exercise physiologist and owner of Fitness for Women in Cincinnati. It also boosts energy, reduces stress and helps you get in shape faster postpartum. (Anecdotal evidence also indicates that prenatal exercise makes for a shorter, easier labor.)

If you're feeling sick, at least walk, if only in 10-minute spurts. Whatever you do, monitor the intensity. Jeffreys suggests using the Borg Scale, which allows you to rate your exertion level from 1 to 10. Sitting would be a 1; an all-out sprint, a 10. If you worked out before becoming pregnant, stay between 3 and 5. If you're new to exercise, aim for 3.

RELATEDIs It Safe to Exercise During Pregnancy?

Job Concerns

Before the first trimester is over, visit your company's human resources department to find out how much maternity leave you'll have and whether it will be paid, unpaid or a combination of both. "You also need to think about your work environment, including chemical exposures, stress and physical demands," says nurse-midwife Low. Try to avoid heavy lifting or standing for long stretches at a time.

Stress-related risks, such as demanding deadlines, long commutes and grueling hours, are less tangible but shouldn't be ignored. Put your feet up on a footstool several times a day, ask for help and delegate, if possible.


Although leaking urine shouldn't be an issue in this trimester, it's never too soon to start strengthening your pelvic-floor muscles. Contract and relax them throughout the day, as though you're stopping and starting the flow of urine.

RELATED: How to Do Kegel Exercises

Labor Prep

Women generally start taking childbirth-prep courses, such as Bradley or Lamaze, during the second trimester, but classes fill up quickly. Research the options in your area (your doctor or midwife and local hospitals probably have lists), and sign up early. While you're at it, look into breastfeeding and newborn-care classes, hospital tours and, if needed, big-sibling classes.


While some women feel sexy when they're pregnant and enjoy not having to fuss with birth control, others don't want to do anything in bed but sleep. If you've lost your libido, don't fret; you'll probably find it in the second trimester, which many women call the honeymoon period of pregnancy.


You probably won't look pregnant until after your fourth month, when your uterus outgrows the pelvic cavity, but that doesn't mean you'll be able to wear your clothes comfortably until then. Increased estrogen levels promote fat storage in several places, including the waistline.

RELATED6 Surprising Benefits of Pregnancy

Telling People

Deciding when and with whom to share your news is a very personal decision, but there are a few things to consider. Keeping your pregnancy a secret for a while will give you and your partner some time to absorb the idea privately. While some women wait until the risk of miscarriage drops markedly (at 14 weeks), others spill the beans right away because they'd tell their friends anyway if they miscarried. Telling co-workers is trickier.

You may find that your employer expects the news to be followed by the details of your maternity leave, but you may not have decided yet when to return to work—if ever.

Harmful Stuff to Avoid Your First Trimester

  • Alcohol, cigarettes, illicit drugs
  • Unheated deli meats, soft-cooked or raw eggs, raw or undercooked meats, raw sprouts
  • Handling cat litter or gardening without gloves
  • Herbal supplements and teas
  • Hot tubs and saunas
  • King mackerel, shark, swordfish and tilefish; raw oysters, mussels and other mollusks
  • Oil-based paints, lead, mercury (found in some latex paints), chemical solvents, oven-cleaning products and dry-cleaning chemicals
  • Over-the-counter and prescription medicines not approved by your doctor
  • Soft cheeses, such as brie and feta; unpasteurized milk and juice
  • Unnecessary X-rays

Read more about what's safe and what's not during pregnancy: 

Fit Pregnancy


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