The pregnancy cycle is full of incredible changes for both mother and baby.

One simple word summarizes pregnancy — change. As your baby grows inside, you grow inside, outside and literally all over — mentally and physically. The big theme of your pregnancy will be transformation. Your body will change right before your eyes and your life will be altered forever because you now have the most magnificent privilege of growing and parenting a human being.

0-3 Months

This little person inside you multiplies by millions of cells per minute. By the end of the first month, most of baby’s major organs, though tiny, are already in place. By five weeks baby is about the size of an apple seed, by eight weeks the size of an olive and by twelve weeks baby really looks like a miniature baby from head to toe. One of the fastest-growing organs in baby’s body is the brain. Baby’s brain growth outpaces that of other organs, occupying around half of baby’s total size. Imagine this budding baby’s brain working overtime to make 250,000 new brain cells every minute by the time baby is only three inches long; and, by 12 weeks, you can hear baby’s heartbeat on ultrasound and may even see whether you are having a boy or a girl.

Since there is a lot going on inside, a mother’s body quickly accommodates to make all the extra fluids and nourishment the rapidly growing baby needs. While you may not yet show, your body tells you that something magnificently different is going on inside, and a queasy gut is usually the first sign. It’s no longer called “morning sickness” since this queasiness can occur any time of the day. The new term is pregnancy-induced nausea (PIN), attributed to the rising levels of baby-growing hormones. The earliest signs of PIN are hypersensitivity to odors and aversions to certain foods.

Food cravings peak during the first three months as your gut continually reminds you that you are pregnant. Around the third month your body changes. Usually by the end of the third month breasts get tender as they get fuller and heavier. Since the breast tissue needs more blood supply to grow those milk ducts, you may notice a more prominent spiderweb-like network of veins just beneath the skin.

4-6 Months

By four months of age your baby is about the size of a plum, weighing in at three to four ounces. Arms start waving and feet start kicking. Newly-found fingers may make a fist, and tiny thumbs may find their way to an open mouth. This is when hearing develops, enabling baby to react to sounds. By the fifth month, baby weighs in around 12 ounces and is half as long as it will be at birth, or about the length of a banana. During the fifth month get ready to feel your little kickboxer.

Between the fourth and fifth months you’ll feel the bump getting bigger. The middle trimester is often a more gut-friendly time, a stage that many mothers most enjoy.

The first peek at your baby by ultrasound, feeling the bulge, hearing the heartbeat and feeling the kicks, are literally your wake-up call that a lot is going on in there. For many mothers this is when baby bonding really takes off.

Toward the end of your middle trimester, the uterus is about the size of a cantaloupe and will ascend to the level of your navel. This is also a time when your brain starts turning inside to focus on that little person inside. “Mommy brain” begins. Your brain becomes so focused on being pregnant that it may have a hard time switching to other decisions not related to baby. Neuroscientists at the National Institutes of Mental Health have proven what new mothers have long suspected: A pregnant woman’s brain changes on the way to growing and caring for her baby. New mothers actually grow more gray matter in the areas of the brain most involved in caring for their baby.

The middle trimester is also when experienced mothers use walking as one of their top stressbusters. Increasing blood flow to the brain through exercise stimulates neurochemicals that have a natural calming effect. One of the healthiest therapies for pregnant mothers, especially when stressed, is what we call flotation therapy — the swimming pool.

6-9 Months

This is when baby and mother go through a huge growth spurt. Baby is likely to gain a couple of pounds a month; triple that for mommy. As babies double their weight and lengthen their limbs, they need more room to stretch, and your body will feel it.

You’ll walk differently, eat differently and sleep differently. You will naturally feel thirstier because a bigger baby needs to refill amniotic fluid. You may notice leg swelling and, because of the bump, your body will naturally be off-center. As your ligaments are stretching — literally for the final stretch — it’s normal to walk with a wide gait or waddle. You may also notice baby dropping down lower in your pelvis as it starts maneuvering into a position for delivery. At this point, the bump now looks lower.

This is a time to rest and nest. It’s normal to feel impatient in anticipation to get your baby out.   “I’m so ready!” is a common feeling at this stage.

Martha Sears, RN, andBill Sears, M.D., are parents of eight and are the co-authors of The Healthy Pregnancy Book.