Fetal Growth and Development
A Pregnancy Timeline of Unborn Baby's Growth
A full-term pregnancy is considered to be 40 weeks, and a baby is considered premature if born prior to 37 completed weeks. You can determine how many weeks pregnant you are by counting the first day of your last menstrual cycle as day one. Although you were not yet pregnant on that day, this is the method most doctors use in determining your due date. This is called the gestational age method. Because we are giving you a nine-month guide, our Month 1 actually begins with Week 5 of your pregnancy (according to the gestational age method).
Month 1 (Weeks 5-8)
By the end of the first month, the embryo has a head, trunk, and little buds that will turn into arms and legs. Your baby’s heart already began beating on the 25th day of your pregnancy, but the umbilical cord is just now beginning to form. The baby is about ½ inch long and weighs less than 1 ounce.
At this stage you are often unaware that you are pregnant, but will soon miss your first period. You may also feel slight breast tenderness or mild aching in your lower abdomen.
Month 2 (Weeks 9-12)
At the end of this month, the embryo is called a fetus. Your baby has a heart, stomach, and other organs and systems, but they are not well-formed. The eyelids are formed, but they are sealed shut. During this period, ears, ankles, wrists, fingers, and toes appear. Your baby is a little more than 1 inch long and still weighs less than 1 ounce.
You may begin to feel queasy and notice that certain smells and tastes bother you because of your changing hormones. An increased pressure on the bladder from the developing fetus will result in additional trips to the restroom.
Month 3 (Weeks 13-16)
Baby’s fingers and toes have soft nails, and there are 20 buds for future teeth. Hair starts to appear on the head, and the kidneys develop and send urine into the bladder. As early as the tenth or twelfth week, you may be able to hear your baby’s heartbeat with a highly sensitive instrument called a Doppler, which your doctor will place on your abdomen during your prenatal visit. By the end of this month, your baby is completely formed, 4 inches long, and weighs a little more than 1 ounce.
This is the first month in which you may truly feel “pregnant,” as changes in your skin, nails, hair, and breasts become noticeable. As the uterus grows to the size of a grapefruit, you will find that your clothing begins to feel tighter – a sign of things to come.
Month 4 (Weeks 17-20)
Your baby has a strong heartbeat now and moves, kicks, sleeps, wakes, swallows, and even hears your voice. Baby is covered with fine hair called lanugo. You may be able to feel your baby move during this month. The movement will at first feel like a flutter. Your baby has pink, thin skin is 6 to 7 inches long and weighs about 5 ounces.
You can expect to feel great this month and will be full of energy. You will be eager to tell the world that you are expecting, yet may experience occasional feelings of anxiety.
Month 5 (Weeks 21-24)
Your baby grows a lot now, and organs mature. The baby sleeps and wakes in a regular pattern, which you will come to know. If you have an ultrasound during the fifth month and your baby is awake, you may be able to see arms, legs, and mouth move. Your physician may also be able to tell you if you are having a boy or a girl. At the end of the fifth month, your baby is 8 to 12 inches long and weighs between ½ and 1 pound.
As your baby grows, so will you. Weight gain becomes significant and you can expect to gain approximately 15 pounds. Occasional mild discomforts, such as backache or heartburn, may also surface.
Month 6 (Weeks 25-28)
Your baby becomes much more active, rolling upside down and side to side. Eyelashes and eyebrows are growing. Thumb-sucking may even occur during this time. At the end of the sixth month, your baby is approximately 12 inches long and weighs about 1 ½ pounds.
The extra weight you are carrying may be noticeable to you in your face, thighs and upper body. Naturally, your uterus becomes larger, too. Pigment changes may be observed, with a dark stripe from your belly button to the groin and/or with the “mask of pregnancy” – a darkened area over the cheeks.
Month 7 (Weeks 29-32)
Your baby will likely begin kicking vigorously, if such activity hasn’t already begun. The baby is able to see and is coated with a waxy substance called vernix caseosa, which protects the skin. A layer of fat is building, which will help the baby maintain a consistent body temperature after birth. Your baby weighs about 2 pounds at the end of this period and is 14 to 15 inches long.
As birth draws closer, you may feel physically uncomfortable – with backaches, shortness of breath or soreness in your lower ribs – as well as nervous about labor and delivery. Attending childbirth education classes will help you to prepare for your baby’s birth and reduce the anxiety you may feel. It is common to experience Braxton-Hicks contractions this month – mild, “practice” contractions felt in the lower abdomen. These contractions are a good motivator to practice the coping techniques you are learning in class.
Month 8 (Weeks 33-36)
You may feel a foot up around your ribcage this month as the baby grows. Your baby may have turned head-down in preparation for the birth. By week 36, the baby is about 16 inches long and weighs approximately 3 ½ to 4 pounds.
Although you may feel “ready” for pregnancy to be over, your baby does not. Be alert to signs of preterm labor. Fatigue, backache, Braxton-Hicks contractions, constipation, and frequent urination are common at this point. The simple act of getting out of bed may be a chore. Try to rest whenever you can, and remember to eat small, nutritious meals and drink plenty of water.
Month 9 (Weeks 37-40)
Your baby is fully formed. The fingernails are surprising long, and it’s not unusual for babies to scratch themselves. The vernix caseosa has mostly disappeared. Your baby will gain approximately 2 pounds this month and measure between 19 to 21 inches long.
You are in the home stretch! You may find yourself “counting down” the days. This is the time for final preparations. Make sure your birth plan is in order, pack your bags, practice your breathing and get ready for the birth – an experience you will always remember!
From the size of a pea to a full-grown little person, your baby is ready to meet you and the rest of the world.