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Week 12
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How Big Is Your Baby?

Your baby weighs between 0.3 and 0.5 ounce (8 to 14g), and crown-to-rump length is almost 2.5 inches (61mm). As you can see on page 110, your baby's size has almost doubled in the past 3 weeks! Length of the baby is a better measure at this time than fetal weight.

How Big Are You?

By the end of 12 weeks, your uterus is too large to remain completely in your pelvis. You may feel it above your pubic bone (pubic symphysis). The uterus has a remarkable ability to grow while you're pregnant. During pregnancy, it grows upward to fill the pelvis and abdomen, and returns to its usual size within a few weeks after delivery.

Before pregnancy, your uterus is almost solid. It holds about 0.3 ounce (10ml) or less. The uterus changes during pregnancy into a comparatively thin-walled, muscular container big enough to hold the fetus, placenta and amniotic fluid. The uterus increases its capacity 500 to 1000 times during pregnancy!

The weight of the uterus also changes. When your baby is born, your uterus weighs almost 40 ounces (1100g) compared to 2.5 ounces (70g) before pregnancy.

The uterine wall grows during the first few months of pregnancy due to hormonal stimulation by estrogen and progesterone. Later in your pregnancy, the growth of the baby and the placenta stretch and thin the uterine wall.

How Your Baby Is Growing and Developing

Few, if any, structures in the baby are formed after this week in pregnancy. However, the structures already formed continue to grow and to develop.

At your 12-week visit (or close to that time), you'll probably be able to hear your baby's heart beat! It can be heard with doppler, a special listening machine (not a stethoscope). It magnifies the sound of your baby's heartbeat so you can hear it.

The skeletal system now has centers of bone formation (ossification) in most bones. Fingers and toes have separated, and nails are growing. Scattered rudiments of hair appear on the body. External genitalia are beginning to show distinct signs of male or female sex characteristics.

The digestive system (small intestine) is capable of producing contractions that push food through the bowels. It is also able to absorb glucose (sugar).

At the base of your baby's brain, the pituitary gland is beginning to make many hormones. Hormones are chemicals that are made in one part of the body, but their action is exerted on another part of the body.

Other things are also happening. The fetal nervous system has developed further. Your baby is moving inside your uterus, but you probably won't feel it for a while yet. Stimulating the fetus in certain spots may cause it to squint, open its mouth and move fingers or toes.

The amount of amniotic fluid is increasing. Total volume is now about 1.5 ounces (50ml). At this time, the fluid is similar to maternal plasma (the noncellular portion of your blood), except it contains much less protein.

Changes in You

You are probably starting to feel better than you have for most of your pregnancy. At this point, morning sickness often begins to improve. You aren't extremely big and are probably still quite comfortable.

You may be wearing maternity clothes. If it's your first pregnancy, you may still be wearing regular clothes. If you've had other pregnancies, you may start to show earlier and to feel more comfortable in looser clothing.

You may be getting bigger in places besides your tummy. Your breasts are probably getting larger. They may have been sore for some time. You may also notice weight gain in your hips, legs and at your sides.

Skin Changes

Your skin may change during pregnancy. In many women, skin along the midline of the abdomen becomes markedly darker or pigmented with a brown-black color. It forms a vertical line called the linea nigra.

Occasionally irregular brown patches of varying size appear on the face and neck called chloasma or mask of pregnancy. These disappear or get lighter after delivery. Oral contraceptives may cause similar pigmentation changes.

Pamela was concerned with a red rash on her neck, face, upper chest and arms. After examining her, I told her she had vascular spiders (also called telangiectasias or angiomas). They are small, red elevations on the skin, with branches extending outward. The condition develops in about 65% of white women and 10% of black women during pregnancy. She was relieved when I reassured her it wasn't serious.

A similar condition is redness of the palms, called palmar erythema. It is seen in 65% of white women and 35% of black women.

Vascular spiders and palmar erythema often occur together. Symptoms are temporary and disappear shortly after delivery. The occurrence of either condition is probably caused by high levels of estrogen during pregnancy.

How Your Actions Affect Your Baby's Development

Some women have the false notion they can eat all they want during pregnancy. Don't fall into this trap! First, it's unhealthy for you and your baby if you gain a great deal of weight during pregnancy. It makes carrying your baby more uncomfortable, and delivery may be more difficult. Second, it will be hard to shed the extra pounds after pregnancy. After their baby is born, most women are anxious to return to ônormalö clothes and to look the way they did before pregnancy. Having to deal with extra weight can interfere with reaching this goal.

Junk Food

Is junk food your kind of food? Do you eat it several times a day? Pregnancy is the time to break that habit!

Now that you're pregnant, your dietary habits affect someone besides just yourselfùyour growing baby. If you're used to skipping breakfast, getting something ôfrom a machineö for lunch, then eating dinner at a fast-food restaurant, it could be harmful to your pregnancy.

What and when you eat becomes more important when you realize how your actions affect your baby. Proper nutrition takes some planning on your part, but you can do it.

If you work, take healthful foods that you like with you for lunches and snacks. Stay away from fast food and junk food.

Late-Night Snacks

Late-night, nutritious snacks are beneficial for some women. However, for many women, snacking at night is unnecessary. If you're used to ice cream or other goodies before bed, you may pay for it during pregnancy with excessive weight gain. Food in your stomach late at night may also cause you more distress if you suffer from heartburn or nausea and vomiting.

You Should also Know

Fifth Disease

Fifth disease, also called parvo virus B19, was the fifth disease to be described with a certain kind of rash. It is a mild, moderately contagious airborne infection. Fifth disease spreads easily through groups, such as classrooms or day-care centers.

The rash looks like reddened skin caused by a slap. The reddening fades and recurs, and lasts from 2 to 34 days. There is no treatment.

This virus is important during pregnancy because it interferes with the production of red blood cells in the woman and the fetus. If you believe you have been exposed to fifth disease during pregnancy, contact your healthcare provider. A blood test can determine whether you have had the virus. If you haven't, your healthcare provider can monitor you to detect fetal problems. Some fetal problems can be dealt with before the baby is born.

Auto Safety during Pregnancy

Women often ask me about driving and about using seat belts and shoulder harnesses during pregnancy. Wearing safety restraints dramatically decreases the incidence of injury in an accident. More than 50,000 deaths and 2-million injuries are directly related to auto accidents every year. Wearing a seat belt and shoulder harness can decrease these losses.

Many women have told me they believe using a safety restraint might be harmful to their pregnancy. Here are some excuses I commonly hear (and my answers) about using seat belts and shoulder harnesses in pregnancy.

ôUsing a safety belt will hurt my baby.ö

There is no evidence their use will increase the chance of fetal or uterine injury. Your chance of survival with a seat belt is better than without one. Your survival is important to your unborn baby.

ôI don't want to be trapped in my car if there is a fire.ö

Few automobile accidents result in fires. Even if a fire did occur, you could probably undo the restraint and escape if you were conscious. Ejection from a car accounts for about 25% of all deaths in automobile accidents. Seat-belt use prevents this.

ôI'm a good driver.ö

Defensive driving helps but doesn't prevent an accident.

ôI don't need to use a safety belt; I'm just going a short distance.ö

Most injuries occur within 25 miles of home.

A few studies have been done on pregnant women who used seat belts. In one California study, only 14% of all pregnant women used seat belts compared to 30% of nonpregnant women. We know the lap/shoulder seat-belt system is safe to wear during pregnancy, so buckle up for you and your baby.

Infant-Restraint Seats

It isn't too early to think about infant- and child-restraint systems. Some people believe they can hold their baby safely in an accident. Others say their child won't sit still in a restraint.

In an accident, an unrestrained child becomes a missile. The force of a crash can literally pull a child out of an adult's arms! One study showed more than 30 deaths a year occur to unrestrained infants going home from the hospital after birth. In nearly all cases, if the baby had been in an approved infant-restraint system, he or she would have survived the accident.

Start early to teach your child safety. If you always place your child in a restraint system in the car, it will become a natural thing to do. You can increase your child's acceptance of a restraint if you wear seat belts, too!

Many states now have infant-restraint laws. Call your local police department or hospital for further information.

Many hospitals require you to take your baby home from the hospital in an approved infant-restraint system. If you want additional information, a pediatrician or the American Academy of Pediatrics can provide a list of safe child- and infant-restraint systems. Consumer magazines rate them quite frequently. Check your local library.

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