Weeks FAQs

Weeks FAQs

What is the baby's development week by week?

An OB or midwife will estimate weeks by gestational age (or menstrual age), which is calculated from the first day of a woman’s last period. Women with high risk pregnancies may also see a perinatologist (doctors who specialize in fetal development). Perinatologists measure weeks in terms of the actual embryo or fetal development they can see using an ultrasound (called conceptual age). OBs also sometimes “adjust” their weeks estimate after the first few ultrasounds and measure by conceptual age.

What is the baby's development timeline?

Babies are all unique. But growth and development in the womb happens on a standard and predictable timeline, from egg fertilization to lung maturation. Sometimes called a pregnancy timeline, the fetal development timeline establishes set points during the pregnancy that fetal growth milestones should occur. If what doctors can see on ultrasounds and measure with blood tests isn’t matching the standard development timeline, it’s a signal that adjustments may be needed in a woman’s prenatal care.

When will I start to feel the baby move?

First-time moms often won’t feel the baby move until around 20 weeks, but every mother’s experience is different. Most second or third time moms will be able to feel movement sooner, around week 15.

How can I tell how many weeks pregnant I am?

Before the first OB ultrasound, the only way to know how many weeks a woman is pregnant is to count from the first day of her last period. Of course, the actual pregnancy didn’t start until about 2 weeks later, but that is how gestational age is calculated. After a few ultrasounds, your OB may adjust your “weeks pregnant” to match the actual growth and development they can see and measure—but usually only by a week or two. From that point it’s just a matter of adding each week that passes.

First Trimester

What is the baby's development at 1 week?

There actually is no baby yet at week one. It seems strange, but at one week pregnant, women are actually not pregnant yet. Conception usually happens about two weeks after the start of a woman’s last period. Since the actual date can’t be known when the egg was fertilized by a sperm and then implanted in the uterus, pregnancy is calculated from the first day of a woman’s last period. So “week 1” is that last period.

What is the baby's development at 2 weeks?

Like week 1, women are actually not pregnant yet during week 2—or at least, not for the full week. At some point during this week, the egg left the ovary (ovulation). It then ventures into the fallopian tube sometime in the next day or two where it waits to be fertilized.

What is the baby's development at 3 weeks?

Week 3—still not pregnant. But, things are moving along nicely. A particularly healthy and energetic sperm has made its way into the fallopian tube. It was a long journey that started as early as 5 days before. The sperm fertilizes the egg and forms a zygote, which then travels down the fallopian tube and into the uterus. It is at this stage that the baby’s gender is determined, and identical twins can be formed (if the zygote divides).

What is the baby's development at 4 weeks?

Depending on the timing, implantation may occur during week 3 or week 4. But for the purposes of this guide, we have placed it in week 4. By week 4, the zygote has divided multiple times until it is a little ball of cells called a blastocyst. It attaches to the wall of the uterus (endometrium) and starts to burrow in—a process called implantation. It is at this point (implantation) that women are officially pregnant. A small group of cells at the innermost part of the blastocyst is the start of the embryo. The outer layer becomes the placenta. The entire blastocyst is about the size of a poppy seed. Most pregnancy tests will register this as positive.

What is the baby's development at 5 weeks?

Week 5 is a very busy week. The blastocyst is now an embryo, and both it and the placenta are growing fast. So fast, that hormone levels spike, signaling the woman’s body to stop producing eggs and halt her period. The brain, spine, and heart have started to form, and by the end of this week, the heart is beating. The embryo is about the size of a sesame seed.

What is the baby's development at 6 weeks?

Now the size of a lentil (1/4 inch), the embryo has a regular heartbeat of about 110 beats per minute. The eyes, nose, ears, and arms are forming, and the intestines are starting to develop. A hollow tube that will become the brain and spinal cord starts to close. It can look a bit like a tail, which is why this is sometimes referred to as the tadpole stage.

What is the baby's development at 7 weeks?

Pea-sized at 7 weeks, the embryo has doubled in size. The head, hands, and feet start to take shape, and the brain forms five distinct areas. Facial features are also developing, and both movement and heartbeat can usually be detected during an ultrasound. Lung development starts gearing up.

What is the baby's development at 8 weeks?

At 8 weeks, the embryo is about the size (and shape) of a kidney bean. The tail is gone and the baby is moving around (although moms won’t be able to feel it yet). Nerve cells are forming pathways, and the breathing tubes form from the throat to the developing lungs. Fingers are forming, and the eyes, nose, and upper lip are established.

What is the baby's development at 9 weeks?

9 weeks is all about the toes! Eyelids and elbows also form and all of the essential organs have begun their development. About the size of a grape, the embryo has earlobes and a large head, but not much of a chin yet.

What is the baby's development at 10 weeks?

The 10th week is the transition from embryo to fetus, with the end of the week being the official beginning of the fetal stage. There are more distinct facial features and eyelids that close. Elbows can bend and fingerprints start to form. Bone cells start to replace cartilage and fingernails and toenails appear.

What is the baby's development at 11 weeks?

At 11 weeks, the fetus is kicking up a storm—that mom still can’t feel. The diaphragm develops and the eyes close. They’ll stay closed until about week 25. While gender was determined way back in week 3, the genital organs are just starting to form. The fetus has a broad face and a very large head—about half of its walnut-sized length. Breathing movements and swallowing become possible, and the fetus is able to open its mouth.

What is the baby's development at 12 weeks?

By 12 weeks, organs are not only formed, but functioning. The thyroid is making thyroid hormones, the pancreas is making insulin, and the kidneys are producing urine. For the first time, the heartbeat can be heard with a fetal monitor. Fingers can open and close, toes start to curl, and reflexes kick in. Still only the size of a lime, mom is not likely to feel any movement, but if she pokes her belly, the baby will feel it.

What is the baby's development at 13 weeks?

Week 13 marks the end of the first trimester. The baby is about the size of a kiwi fruit and just about all of its many parts are developed and functioning, though very small. The skin is translucent, making veins and organs visible. Bones are hardening, limbs are more defined and the neck starts to elongate. If the baby is female, she already has ovaries containing more than 2 million eggs.

Second Trimester

What is the baby's development at 14 weeks?

By 14 weeks, the fetus has 20 buds that will become baby teeth, a liver making red blood cells, and the ability to make a fist. Fine hair, called lanugo, starts to form all over the body. About the size of a lemon, the baby’s brain is firing up. Facial expressions and thumb-sucking are now possible.

What is the baby's development at 15 weeks?

The size of a mango at 15 weeks, the baby can now sense light. Some moms will begin sensing movement at this stage, but many don’t feel anything until about week 20 or later. Baby moves and stretches a lot as bones become harder and muscles develop.

What is the baby's development at 16 weeks?

At 16 weeks, the baby is about as long as an avocado and becoming more coordinated. The eyes are moving now, although they won’t reopen until around week 25. Hearing begins to form, and the lungs enter their second stage of development. The head is more upright now, and the ears are just about in their final position.

What is the baby's development at 17 weeks?

Week 17 reveals a lot more movement, including rolls and flips, which most women won’t be able to feel. The heart is getting stronger, pumping about 100 pints of blood per day. The skeleton is formed and hardened, and the umbilical cord becomes thicker and stronger. Baby is about the size of a pear, and hearing begins to develop.

What is the baby's development at 18 weeks?

The size of a sweet potato at 18 weeks, the baby is now beginning to hear sounds. The ears are starting to stand out more from the head and brain development hits a milestone. A protective coating, called myelin, starts to form around the nerves.

What is the baby's development at 19 weeks?

The pace of growth starts to slow down around week 19. A protective coating forms around the baby’s new skin to protect it from the amniotic fluid. All of the baby’s senses are developing—smell, vision, touch, taste, and hearing. It’s possible babies can even hear mom’s voice, if she talks or sings to them. If this is not the mom’s first pregnancy, she’ll be more likely to be able to feel movements at this stage. Legs are now longer than the arms, and kicking becomes more common.

What is the baby's development at 20 weeks?

20 weeks marks the halfway point, as well as the start of hair growth on the scalp. The baby is about the length of a banana and may even have faint eyebrows. The digestive system starts making meconium, which is a dark, sticky fluid that will become the baby’s first poop. Feeling the baby move becomes more common around this time. Regular sleeping and waking cycles begin, and it’s possible to wake the baby up with mom’s movement or outside noise.

What is the baby's development at 21 weeks?

Baby’s movements at 21 weeks are becoming more forceful—jabs and kicks, rather than flutters. For moms who can feel them, patterns may emerge. About the length of a red pepper and testing out its growing body, the baby may even hiccup! Some women feel Braxton Hicks contractions (false labor) around this time.

What is the baby's development at 22 weeks?

At 22 weeks, babies are just barely developed enough to have a chance of survival outside the womb. The lungs are developing quickly, and baby starts to make the proteins it will need to breath after birth. Features have become distinct as the eyes, nose, lips, and eyebrows now reach their final shapes. Eye color won’t come until a bit later, but the eyes are still closed. Most moms will be able to feel the baby’s movements. The baby is about the length of a spaghetti squash, and the heartbeat can be heard with a stethoscope for the first time.

What is the baby's development at 23 weeks?

Eggplant-sized at week 23, baby’s hands and feet start to develop the deeper ridges that become part of their first handprints and footprints. The brain is more developed and baby can not only hear parents, but is starting to recognize their voices. Rapid eye movements begin during sleep, which may mean baby is dreaming. Doctors can see the baby’s full nerve tract that separates the two halves of the brain (called a corpus callosum) on an ultrasound for the first time.

What is the baby's development at 24 weeks?

Blood vessels in the baby’s skin have formed at 24 weeks, giving the baby a pinkish-red, translucent glow. Wrinkles have also formed in preparation for baby to start putting on weight in the upcoming weeks. Baby is about the size of a full ear of corn. The nostrils open, and they inhale and exhale amniotic fluid the way they will breathe once they’re born.

What is the baby's development at 25 weeks?

At 25 weeks, baby is now the size of an acorn squash and able to stick out its tongue! Baby’s grip is also stronger, which may lead to some practice tugging on the umbilical cord. Lung development is nearly complete, and the bone marrow will be making blood cells by the end of this week. Hair is just starting to come in as the baby starts to store fat and fill out, looking more and more like a newborn every day. The eyes open again for the first time in about 10 weeks.

What is the baby's development at 26 weeks?

With a rapidly growing brain, baby may startle at loud noises at 26 weeks. Air sacs are developing in the lungs as baby continues to practice breathing amniotic fluid. After being closed for so long, baby’s eyes now open and close at will. The length of a scallion, baby is growing hair and gaining weight—most will weigh about 2 pounds by the end of this week.

What is the baby's development at 27 weeks?

Week 27 marks the last week of the second trimester. Baby is about the size of a head of cauliflower, with an immature, but fully-formed respiratory system. Sleeping and waking on a regular schedule, baby may recognize more than just mom’s voice. Most babies born now could survive outside the womb without medical help. But there’s still lots of growing and maturing to do.

Third Trimester

What is the baby's development at 28 weeks?

28 weeks old, the baby gets waterproofed—a waxy substance covers their skin, believed to both protect against and prevent infections. Eyesight is developing and shapes of light may be visible. The nervous system is now controlling some of baby’s functions, including body temperature. Baby is as long as a large eggplant or chinese cabbage.

What is the baby's development at 29 weeks?

The average baby at 29 weeks weighs 3 pounds and is more than 15 inches long—about the size of a butternut squash. The head is growing to make room for the developing brain, as the rest of the body continues to mature.

What is the baby's development at 30 weeks?

At 30 weeks, babies might be giving you a kick to let mom know they’re awake. With almost a full head of hair, they’ll start to gain about a 0.5 pound per week. There is less of a cushion of amniotic fluid now, which will make mom aware of baby’s every move. The cabbage-size bundle that mom is carrying will be obvious to pretty much everyone.

What is the baby's development at 31 weeks?

Baby’s bones are fully formed at 31 weeks, although they need to continue to harden. Baby weighs about as much as a coconut and is longer than a bowling pin—on average 4 pounds and 16 inches long this week. Baby can now turn its head from side to side and has a nice, protective layer of fat under its skin.

What is the baby's development at 32 weeks?

At 32 weeks, babies are starting to put on muscle, as well as fat. The baby will gain about a third of its weight between now and the birth. Baby’s breathing becomes more rhythmic and the body starts storing iron, calcium, and phosphorus. The soft, fine hair that covered the baby’s skin (lunago) may start falling off this week. If baby is male, his testicles will descend sometime this week or next week.

What is the baby's development at 33 weeks?

Babies weigh an average of almost 5 pounds by week 33, and are as long as a pineapple. The bones have mostly hardened, except for the skull, which remains soft and flexible until after birth so the baby can fit through the birth canal. If male, the testicles have usually descended by this week.

What is the baby's development at 34 weeks?

At 34 weeks, baby has probably settled into a vertical position, either heads up or heads down. (Don’t worry, babies that are heads up now can still turn up to a few hours before birth). The baby may drop too, sitting lower (and less comfortably) into mom’s pelvic area. Babies weigh over 5 pounds on average and are the size of a large cantaloupe. The nervous system and lungs are nearly mature.

What is the baby's development at 35 weeks?

The size of a honeydew, the baby at 35 weeks is still maturing. The kidneys are fully developed, and the liver is starting to function. While the baby keeps putting on weight, it probably won’t grow much more length-wise until after birth. Pressure on the bladder by the baby’s weight can become intense at this stage, but moms may be able to breathe more easily as the baby presses less against the lungs and diaphragm.

What is the baby's development at 36 weeks?

At 36 weeks, baby is about the length of a head of romaine lettuce, but much heavier—more than 6 pounds on average. The skin wrinkles that developed early on are nearly gone, as the baby has plumped up for its entry into the world. Muscles, bones, blood vessels, and even sleep patterns are fully developed. The lunago hair and waxy protectant that covered baby’s skin are disappearing.

What is the baby's development at 37 weeks?

Braxton Hicks contractions (false labor) become more common at 37 weeks. The baby’s brain and lungs continue to mature, and it is probably running out of room to move. That means more stretches and wiggles and fewer kicks. Weighing more than 6.5 pounds on average, the baby looks ready to go.

What is the baby's development at 38 weeks?

At week 38, baby’s nails may be long enough to need a trim and head hair is more course and thick. The fine hair that was covering baby’s body (lunago) is now gone except for the upper arms and shoulders. Breast buds appear on both boys and girls. The baby can decide to come any time now, but will be considered early until next week.

What is the baby's development at 39 weeks?

Babies born at 39 weeks are considered full term. But that doesn’t mean that baby will cooperate. The size of a small pumpkin, mom is probably more than ready. But don’t worry if baby decides to wait it out. There is a lot of maturity going on in these last few weeks.

What is the baby's development at 40 weeks?

At week 40, baby’s skull bones are still not fused, which allows them to overlap if the birth canal is a bit strained during labor. This is called “molding” and it’s why some newborns heads are pointy. This is completely normal and temporary. Babies are supposed to be born sometime during the 40th week—averaging about 7 and a half pounds and measuring 20 inches long. But many babies don’t stick to this schedule. Heredity, nutrition, and the mom’s health all play a role on when baby will come.

What is the baby's development at 41 weeks?

At 41 weeks, the baby is still considered full term. That’s because pregnancy start dates are an estimate, so the due date might not be accurate. What doctors decide to do if mom goes past her due date will depend on both mom and baby’s overall health. Expect frequent check-ins with your OB.

What is the baby's development at 42 weeks?

Babies who haven’t been born by week 42 are officially late term. This puts both mother and baby at more risk, so doctors may suggest inducing labor.

What questions should I ask my OB or midwife at 36 weeks?

The 36 week prenatal visit is an important time for women to set the stage with their OB or midwife for their upcoming delivery. Some questions to ask:

  • What signs and symptoms should I report to you immediately? If I can’t reach you, should I go to the hospital?
  • Is there anything that can help with urinary leakage (or any other symptoms you are experiencing)?
  • Do you need to see me weekly from here on? Why?
  • I know I can’t fly, but can I drive several hours from home?
  • Have I been tested for Group B Streptococcal (GBS) disease?
  • Do I need to take antibiotics to prevent spreading GBS to the baby?
  • What if I go into labor before my GBS test is back?
  • Is the baby’s head down? If not, should I consider a procedure or technique to turn the baby?
    Has the baby dropped?
  • Should I have a 3D ultrasound?
  • Should I plan for cord blood banking or donation?
  • Do I need a shot of RH immunoglobin?
  • What do I need to pay attention to with my baby’s movements?
  • When should I go to the hospital for my delivery?
  • Will you be there throughout my labor?
  • Is there a nurse with me constantly during labor, or do I share nurses with a lot of other patients?
  • What happens if I go into labor in the middle of the night?
  • Can we review my birth plan together now?
  • Can you recommend a pediatrician (if you don’t already have one)?
  • If the baby is male, and I choose to get him circumcised, can this be done in the hospital?
  • I’m planning to breastfeed (or formula feed). What do I need to know now?
  • I’m feeling anxious and a little depressed, should I worry about postpartum depression?

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