Normal Growth of a Baby During Pregnancy

To understand your pregnancy, it is helpful to know how your baby changes month to month during the 9 months you are pregnant.

FIRST MONTH

About 5 to 7 days after the sperm fertilizes the egg, the egg attaches to the lining of the uterus. This process is called implantation. The fertilized egg then begins to grow in the uterus, doubling in size every day. At this stage of development the baby is called an embryo.

Shortly after implantation, the placenta and umbilical cord begin to form. The placenta and umbilical cord provide nourishment and oxygen to your baby and carry away the baby's wastes. Your baby is enclosed in a sac of fluid to protect the baby from bumps and pressure.

In another week the baby has a spinal cord. A few days later five to eight bones of the spinal column (vertebrae) are in place. By the end of your first 6 weeks of pregnancy, your baby has a head and trunk. The eyes and other features begin to form, as do tiny buds that will be the arms and legs. The heart also forms, and it begins to beat on the 25th day after conception (5 to 6 weeks after the last menstrual period).

By the end of 6 weeks your baby is about ½ inch long (1 centimeter) and weighs a fraction of an ounce (or a few grams).

SECOND MONTH

This month is especially critical in the development of your baby. Any disturbance from drugs, viruses, or environmental factors such as pesticides may cause birth defects.

Your baby's development is very rapid during the second month. By the end of the second month, all of your baby's major body organs and body systems, including the brain, lungs, liver, and stomach have begun developing. The first bone cells appear. Eyelids form and grow but are sealed shut, and ears are formed. Ankles, toes, wrists, fingers, and sexual organs develop. If your baby is a boy, his penis begins to appear now.

At the end of the month your baby looks like a miniature human infant. The baby is a little over 1 inch long (3 centimeters) and still weighs less than 1 ounce (30 grams). From now until birth the baby is called a fetus.

THIRD MONTH

By the end of this month, your baby is completely formed. The fingers and toes have soft nails, and tooth buds have formed under the gums. Hair may start to appear on the head, and the head is large compared with the rest of the body. The kidneys develop and start draining urine into the bladder. The baby's heart has four chambers and beats at 120 to 160 beats per minute. The baby may open and close its mouth and start moving its hands, legs, and head. At this point, however, you will not feel this movement.

Your baby is now 4 inches long (10 centimeters) an weighs just a little over 1 ounce (30 grams).

FOURTH MONTH

The baby is completely formed. The skin is pink and somewhat transparent, and eyebrows and eyelashes begin to appear. Your baby now has a strong heartbeat.

The baby moves, kicks, sleeps, wakes, swallows, and passes urine. You may start to feel a slight sensation of movement in your lower abdomen. This feeling is like bubbles or fluttering. When you first feel the baby's movement (called quickening), write down the date. This date helps the doctor determine when you baby is due.

Your baby is now 8 to 10 inches (16 to 25 centimeters) long and weighs about 6 ounces (180 grams).

FIFTH MONTH

Your baby will have a real growth spurt this month. The internal organs are maturing, and the fingernails have grown to the tips of the fingers. The baby starts storing fat beneath the skin. The baby sleeps and wakes at regular intervals and may suck its thumb. You will find that your baby is much more active, turning from side to side and head over heels.

Your baby is now about 12 inches (30 centimeters) long and weighs about 1 pound (500 grams).

SIXTH MONTH

Your baby continues to grow rapidly from now until birth. The skin is wrinkled and red and covered with fine soft hair (lanugo) and vernix (a substance of oil and cells).

By the end of this month, your baby is 11 to 14 inches (27 to 30 centimeters) long and weighs about 1 to 1 and ½ pounds (750 grams). Because your baby is still so small and the lungs are not fully developed, it usually cannot live outside your uterus at this stage without very specialized care.

SEVENTH MONTH

The baby exercises by kicking and stretching. The baby opens and closes its eyes. Calcium is being stored, and the bone centers are hardening. The lanugo begins to disappear from the face, and the baby may have more hair on its head.

Your baby is about 15 inches (37 centimeters) long and weighs 2 to 3 pounds (1000 to 1500 grams). The baby now has a better chance of survival if born early.

EIGTH MONTH

Your baby is getting too big to move around much, but its kicks are stronger, and you may be able to see the outline of a small heel or elbow against your abdomen. If your baby is a boy his testicles descend into his scrotum.

Your baby is now 16 to 18 inches (40 to 45 centimeters) long and weighs about 4 pounds (1800 grams).

NINTH MONTH

Your baby now becomes plumper and gains about ½ pound (200 grams) each week. The baby is getting ready for birth and usually settles into a favorable position, with it's head down against the birth canal and its knees against the nose. The bones of the head are soft and flexible for delivery through the birth canal.

Your baby is now about 20 inches (50 centimeters) long and weighs 6 to 9 pounds (2500 to 4000 grams). Your baby could arrive any time between the 37th week and 42nd weeks of pregnancy.

Adapted from material developed by Clinical Reference Systems, Ltd.

Copyright 1996 Clinical Reference Systems, Ltd.