The following has been adapted from the websites listed at the bottom of the page.
It is important to remember that your due date is only an estimate most babies are born between 38 and 42 weeks from the first day of your last menstrual period (LMP). Only a small
percentage (about 5%) of babies are born on their estimated due date.
A standard way of looking at pregnancy is to divide the pregnancy into trimesters: the first trimester is from week 1 to the end of week 12, the second trimester is from week 13 to the end of week 26, and the third trimester
is from week 27 to the end of the pregnancy.
To help you follow some of the concerns and changes you may encounter during your pregnancy, this section is divided into month-by- month segments. Additional
information about months 1-3 is provided on the page first trimester, months 4-6 on the page second trimester, and months
7-9 on the third trimester.
What is gestational age?
Gestational age is the age of an unborn baby measured in weeks and days, not in months. Since the precise date of conception is seldom known, the age is based on the date of the mother's last menstrual period. Forty
weeks after the first day of the last menstrual period is the estimated due date. An early exam of your uterus and an early positive pregnancy test also help determine gestational age.
The most accurate way to determine gestational age is by an ultrasound exam. The
baby can be measured with ultrasound as early as 5-6 weeks after your last menstrual period.
In a normal pregnancy, about 5-7 days after a sperm fertilizes an egg, the egg implants in the lining of the uterus. The fertilized egg then begins to grow in the uterus. 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, called
the amniotic sac, to protect the baby from bumps and pressure.
In another week the baby has a spinal cord. A few days later, 5-8 bones of the spinal column are in place and nerve development begins. By the end of your first
6 weeks of pregnancy, your baby has a head and trunk, is about 1/2 inch long and weighs much less than an ounce.
During your first month of pregnancy, you may experience fatigue and sleepiness, frequent urination, nausea, vomiting, heartburn, indigestion, bloating, food aversions or cravings, and/or
breast changes. These pregnancy symptoms vary from woman to woman. Emotionally, you may feel irritable, have mood swings, may act irrationally,
and be quick to cry. It is also common to have a variety of feelings about being pregnant, including misgivings,
fear, joy, and elation.
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 to develop. The first bone cells appear during this time. Eyelids form and grow but remain sealed shut. The inner ear is forming. Ankles, toes, wrists, fingers, and sexual organs
At the end of the second month of pregnancy, your baby looks like a tiny human infant. The baby is a little over 1 inch long and still weighs less than 1 ounce. From this point on the developing baby is
called a fetus.
Your baby will be completely formed by the end of the third month. Your baby may have begun moving its hands, legs, and head and opening and closing its mouth, but he or she is still too small for you to feel this movement.
The baby's hands are more developed than the feet and the arms are longer than the legs. Hair may have started to form on the head. Tooth buds have formed under the baby's gums. Vocal cords develop around the 13th week of pregnancy.
Your baby's heart has four chambers and beats at 120 to 160 beats per minute. Kidneys are now developed and start draining urine into the bladder. By the end of this month, the umbilical cord, which carries nutrients to your baby and takes wastes away,
will be fully formed. At the end of your third month, your baby will weigh just over 1 ounce and will be about 4 inches long.
Additional information about months 1-3 is provided on the page first trimester.
The baby's skin in pink and somewhat transparent. Eyebrows and eyelashes begin to appear and buds on the side of the head begin to form into the outer ear. The baby's face continues to develop and the head makes up about half of the
The baby moves, kicks, sleeps, wakes, swallows, and passes urine. You may start to feel a fluttering (called quickening) in your lower abdomen. By the end of the fourth month, your baby will be 8 to 10 inches long
and will weigh about 6 ounces.
The internal organs are maturing. Your baby's fingernails have grown to the tips of the fingers. Fat is now being stored beneath your baby's skin. Your baby is also growing muscle. The blood cells take over the job of
producing blood. Your baby's gall bladder will become functional, producing bile that is necessary for digestion. Milk teeth will begin forming under your baby's gums. Body hair, including eyebrows and eyelashes, are starting to grow.
Your baby sleeps and wakes at regular intervals. You will find that your baby is much more active now and may turn from side to side and head over heels. At the end of the fifth month, you baby will be about 10-12 inches long and will
weigh about 1 pound.
This month continues to be a period of rapid growth. Your baby's skin is wrinkled and red. It is covered with lanugo (fine, soft hair) and vernix (a substance consisting of oil, sloughed skin cells and lanugo). Real hair and toenails
are beginning to grow. Your baby's brain is developing rapidly. Fatty sheaths which transmit electrical impulses along nerves are forming. Meconium, your baby's first stool, is developing. The baby's bones are becoming solid.
Your baby is almost fully formed and looks like a miniature human. By the end of the sixth month, your baby will be around 11 to 14 inches long and will weigh about 1 to 1 1/2 pounds.
Additional information about months 4-6 is provided on the page second trimester.
Your baby's eyes can now open and close and can sense light changes. The lanugo is starting to disappear from the baby's face. Your baby's hearing is getting more sensitive and can hear the outside world. The baby increases kicking
and stretching. By the end of
this month, your baby will be approximately 15 inches long and weigh about 2 or 2 1/2 pounds.
Your baby continues to grow quickly with the bones getting stronger, limbs fatter, and the skin takes on a healthy glow. The brain is now forming its different regions and the brain
and nerves are directing bodily functions. Taste buds are developing. Your baby may now hiccup, cry, taste sweet and sour, and respond to pain, light, and sound. If you are having a boy, his testicles have
dropped from his abdomen where they will then descend into his scrotum. Your baby will be about 16 to 18 inches long and will weigh about 4 pounds at the end of this month.
Your baby is now gaining about a 1/2 pound each week. Your baby is getting fatter and its skin is less rumpled. Typically, the baby is getting ready for birth and is settling into the fetal position with its head down against
the birth canal, its legs tucked up to its chest, and its knees against its nose.
Your antibodies to disease are beginning to flow rapidly through the placenta. Your baby will continue to kick and punch although it will move lower in your abdomen to under
your pelvis (this is a process called "lightening"). You will also feel your
baby roll around as it gets too cramped inside your uterus for much movement. The bones of baby's head continue to be soft and flexible to ease the process
of delivery through the birth canal.
Your baby is now about 20 inches long and weighs approximately 6 to 9 pounds. Your baby may be born anytime between the 37th and 42nd week of pregnancy. Additional information about months 7-9 is provided on the page third
Click on this link for more on labor and delivery.