It may seem strange, but not actually pregnant the first week or two of the time allotted to the pregnancy.
Conception typically occurs about two weeks after the period begins. To calculate the due date, the health care provider will count ahead 40 weeks from the start of the last period. This means the period is counted as part of the pregnancy – even though you weren't pregnant at the time.
The sperm and egg unite in the fallopian tube to form a one-celled entity called a zygote. If more than one egg is released and fertilized, may have multiple zygotes.
The zygote has 46 chromosomes — 23 from woman and 23 from male. These chromosomes contain genetic material that will determine the baby's sex and traits such as eye color, hair color, height, facial features and – at least to some extent – intelligence and personality.
Soon after fertilization, the zygote will travel down one of the fallopian tubes toward the uterus. At the same time, it will begin dividing rapidly to form a cluster of cells resembling a tiny raspberry. The inner group of cells will become the embryo. The outer group of cells will become the membranes that nourish and protect it.
The zygote – by this time made up of about 500 cells – is now known as a blastocyst. When it reaches the uterus, the blastocyst will burrow into the uterine wall for nourishment. The placenta, which will nourish the baby throughout the pregnancy, also begins to form.
By the end of this week, may be celebrating a positive pregnancy test.
The fourth week marks the beginning of the embryonic period, when the baby's brain, spinal cord, heart and other organs begin to form. Baby is now 1/25 of an inch long.
The embryo is now made of three layers. The top layer – the ectoderm – will give rise to a groove along the midline of the baby's body. This will become the neural tube, where the baby's brain, spinal cord, spinal nerves and backbone will develop.
Baby's heart and a primitive circulatory system will form in the middle layer of cells – the mesoderm. This layer of cells will also serve as the foundation for the baby's bones, muscles, kidneys and much of the reproductive system.
The inner layer of cells – the endoderm – will become a simple tube lined with mucous membranes. The baby's lungs, intestines and bladder will develop here.
At week five, the baby is 1/17 of an inch long – about the size of the tip of a pen.
This week, the baby's heart and circulatory system are taking shape. Baby's blood vessels will complete a circuit, and baby’s heart will begin to beat. Although mother won't be able to hear it yet, the motion of the baby's beating heart may be detected with an ultrasound exam.
With these changes, circulation begins – making the circulatory system the first functioning organ system.
Growth is rapid this week. Just four weeks after conception, the baby is about 1/8 of an inch long. The neural tube along the baby's back is now closed, and the baby's heart is beating with a regular rhythm.
Baby is 1/3 of an inch long – a little bigger than the top of a pencil eraser. He or she weighs less than an aspirin tablet.
The umbilical cord – the link between the baby and the placenta – is now clearly visible. The cavities and passages needed to circulate spinal fluid in the baby's brain have formed, but the baby's skull is still transparent.
Eight weeks pregnancy, the baby is just over 1/2 of an inch long.
Baby will develop webbed fingers and toes this week. Wrists, elbows and ankles are clearly visible, and the baby's eyelids are beginning to form. The ears, upper lip and tip of the nose also become recognizable.
As baby's heart becomes more fully developed, it will pump at 150 beats a minute – about twice the usual adult rate.
Baby is now nearly 1 inch long and weighs a bit less than 1/8 of an ounce. The embryonic tail at the bottom of the baby's spinal cord is shrinking, helping him or her look less like a tadpole and more like a developing person.
Baby's head – which is nearly half the size of his or her entire body – is now tucked down onto the chest. Nipples and hair follicles begin to form. Baby's pancreas, bile ducts, gallbladder and anus are in place. The internal reproductive organs, such as testes or ovaries, start to develop.
Baby may begin moving this week, but won't be able to feel for it quite a while yet.
Baby's eyelids are no longer transparent. The outer ears are starting to assume their final form, and tooth buds are forming as well. If baby is a boy, his testes will start producing the male hormone testosterone.
From now until 20th week of pregnancy – the halfway mark – baby will increase his or her weight 30 times and will about triple in length. To make sure the baby gets enough nutrients, the blood vessels in the placenta are growing larger and multiplying.
Baby is now officially described as a fetus. Baby's ears are moving up and to the side of the head this week. By the end of the week, the baby's external genitalia will develop into a recognizable penis or clitoris and labia majora.
Subsequent prenatal visits – often scheduled every four to six weeks during the first trimester – will probably be shorter than the first. Healthcare provider will check the weight and blood pressure, and will discuss the signs and symptoms.
Probably won't need another pelvic exam until later in the pregnancy.
Near the end of the first trimester, can hear the baby's heartbeat with a small device that bounces sound waves off the baby's heart.
As your baby's hearing continues to improve, he or she may pick up your voice in conversations — although it's probably hard to hear clearly through the amniotic fluid and protective paste covering your baby's ears.
Thanks to the millions of motor neurons developing in the brain, your baby can make reflexive muscle movements.
Track your baby's growth . By measuring your abdomen from the top of your uterus to your pubic bone, your health care provider can gauge your baby's growth. This measurement in centimeters often equals the number of weeks of pregnancy.
Listen to your baby's heartbeat. You'll hear your baby's heartbeat, too, thanks to a special device called a Doppler.
Assess fetal movement. Tell your health care provider when you begin noticing flutters or kicks — often by 20 weeks.
If your baby is a boy, his testicles are moving from their location near the kidneys through the groin on their way into the scrotum. If your baby is a girl, her clitoris is now relatively prominent.
Your baby's lungs are more developed, but they're not fully mature. If your baby is born this week, he or she will probably need a ventilator to breathe. Complications such as bleeding in the brain are less likely than they were even a few weeks ago.
Tell yourself that you'll simply do the best you can. There's no right or wrong way to have a baby.
The reality of parenthood may start to sink in as well. You may feel anxious and overwhelmed, especially if this is your first baby. To stay calm, revel in the emotions and sensations of being pregnant.
Write your thoughts in a journal.
Listen to soft music.
Talk to your baby.
Take photos of your pregnant belly to share with your baby one day.