Fetal Development: Pregnancy Stages Month by Month (2023)

When does pregnancy begin?

The beginning of pregnancy is actually the first day of your last menstrual period. This is called gestational age or menstrual age. It's about two weeks before actual conception. As strange as it may seem, the date of the first day of your last period is an important date in determining your due date. Your doctor will ask you about this date and use this to determine how far along your pregnancy is.

How does conception work?

Each month your body goes through a reproductive cycle that can end in two ways. You will either have a menstrual period or become pregnant. This cycle occurs continuously throughout your reproductive years—from puberty in your teenage years to menopause around the age of 50.

There are several steps in a cycle that ends in pregnancy. First, a group of egg cells (called ova) prepare to leave the ovary for ovulation (release of the egg). The eggs develop in small, fluid-filled cysts called follicles. Think of these follicles as small receptacles for each immature egg. From this group of eggs, one will mature and continue the cycle. This follicle then suppresses all other follicles in the group. The other follicles stop growing at this point.

The mature follicle now opens and releases the egg cell from the ovary. This is ovulation. Ovulation generally occurs about two weeks before the start of your next menstrual period. It's generally in the middle of your cycle.

After ovulation, the opened (ruptured) follicle develops into a structure called the corpus luteum. This releases (releases) the hormones progesterone and estrogen. Progesterone helps prepare the endometrium (lining of the womb). This lining is where a fertilized egg settles down to develop. If you don't get pregnant during a cycle, this lining will shed during your period.

On average, fertilization takes place about two weeks after your last menstrual period. When the sperm enter the egg, changes occur in the protein coat of the egg to prevent other sperm from entering.

At the time of conception, your baby's genetic makeup is complete, including its gender. The sex of your baby depends on which sperm is fertilizing the egg at the moment of conception. In general, females have a genetic combination of XX and males have XY. Women mark each egg with an X. Each sperm can be either an X or a Y. If the fertilized egg and sperm are a combination of X and Y, it's a boy. If there are two X's, it's a girl.

What happens right after conception?

Within 24 hours of fertilization, the egg starts dividing rapidly into many cells. It remains in the fallopian tube for about three days after conception. Then the fertilized egg (now called a blastocyst) continues to divide as it slowly travels down the fallopian tube and into the uterus. Once there, its next task is to attach itself to the uterine lining. This is called implantation.

Before implantation, however, the blastocyte breaks out of its protective cover. When the blastocysts come in contact with the endometrium, the two hormones exchange to aid in blastocytic attachment. Some women notice spotting (light bleeding) during the day or two that the implantation takes place. This is normal and nothing to worry about. At this point, the endometrium thickens and the cervix (the opening between your uterus and your birth canal) becomes closed with a mucus plug.

Finally, within three weeks, the blastocytes form a globule, an embryo. At this point, the first nerve cells have formed.

Your developing fetus has already undergone some name changes in the first few weeks of pregnancy. In general, from conception to the eighth week of development, it is called an embryo. After the eighth week, it is called a fetus until it is born.

How early can I know I'm pregnant?

The hormone human chorionic gonadotropin (hCG) is present in your blood from the moment you conceive. This hormone is made by the cells that make up the placenta (source of nutrition for the growing fetus). It is also the hormone detected in apregnancy test. Although this hormone is there to begin with, it takes time for it to build up in your body. It usually takes three to four weeks from the first day of your last period for hCG levels to rise high enough to be detected by pregnancy tests.

When should I tell my doctor about a new pregnancy?

Most healthcare providers will make you wait until you have a positive home pregnancy test. These tests are very accurate once enough hCG is circulating in your body. This can be a few weeks after conception. It's best to call your doctor as soon as you have a positive pregnancy test to schedule your first appointment.

(Video) Fetal development month by month

If you call, your doctor may ask if you're taking a prenatal vitamin. These dietary supplements contain folic acid. It is important that you get at least 400 micrograms of folic acid each day during pregnancy to ensure that the fetal neural tube (beginning of the brain and spine) develops properly. Many healthcare providers suggest you take itprenatal vitaminswith folic acid even without pregnancy. If you didn't take prenatal vitamins before you became pregnant, your doctor may ask you to start taking them as early as possible.

What is the fetal development schedule?

The fetus will change a lot during a typical pregnancy. This time is divided into three phases called trimesters. Each trimester is a set of about three months. Your healthcare provider will likely talk to you about how the fetus is developing in weeks. So if you are three months pregnant, you are around 12 weeks old.

You will see significant changes in the fetus and in yourself during each trimester.

Traditionally, we think of pregnancy as a nine-month process. However, this is not always the case. A full-term pregnancy lasts 40 weeks or 280 days. Depending on how many months pregnant you are (some are shorter, some longer) and what week you give birth, you can be pregnant for either nine or ten months. This is perfectly normal and healthy.

As you near the end of your pregnancy, there are several category names you may hear as you go into labour. These labels divide the final weeks of pregnancy. They are also used to look out for certain complications in newborns. Babies born in the preterm or earlier may be at greater risk of breathing, hearing, or learning problems than babies born a few weeks later in the full term. When looking at these labels, it's important to know how they're written. You may first see the week (38) and then two numbers separated by a slash (6/7). This represents how many days into your pregnancy week you are currently. So if you see 38 6/7, it means you are on the 6th day of your 38th week.

The last weeks of pregnancy are divided into the following groups:

  • Early tenure: 37 0/7 weeks to 38 6/7 weeks.
  • full term: 39 0/7 weeks to 40 6/7 weeks.
  • Late term: 41 0/7 weeks to 41 6/7 weeks.
  • run-on time: 42 0/7 weeks and more.

Talk to your doctor if you have questions about gestational age and due date.

Growth stages month by month in pregnancy

First trimester

The first trimester extends from conception to 12 weeks. These are usually the first three months of pregnancy. During this trimester, the fertilized egg transforms from a small group of cells into a fetus, which gradually begins to have the characteristics of a baby.

Month 1 (weeks 1 to 4)

As the fertilized egg grows, a watertight sac forms around it and gradually fills with fluid. This is called the amniotic sac and helps cushion the growing embryo.

The placenta also develops during this time. The placenta is a round, flat organ that transfers nutrients from the mother to the fetus and waste products from the fetus. Think of the placenta as a source of nourishment for the fetus throughout your pregnancy.

In these first few weeks a primitive face with large dark circles under the eyes will take shape. The mouth, lower jaw and throat develop. The blood cells take shape and the circulation begins. By the end of the fourth week, the tiny "heart" tube is beating 65 times per minute.

By the end of the first month, the fetus is about 1/4 inch long - smaller than a grain of rice.

Month 2 (weeks 5 to 8)

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The facial features continue to develop. Each ear begins as a small fold of skin on the side of the head. Tiny buds form, which eventually grow into arms and legs. Fingers, toes, and eyes also form.

The neural tube (the brain, spinal cord, and other neural tissues of the central nervous system) is now well developed. The digestive tract and sense organs also begin to develop. Bone begins to replace cartilage.

The head is large at this point in relation to the rest of the body. A heartbeat can usually be detected after about 6 weeks.

After the 8th week, healthcare providers refer to it as a fetus instead of an embryo.

At the end of the second month, the fetus is about 1 inch long and weighs about 1/30 ounce.

Month 3 (weeks 9 to 12)

The arms, hands, fingers, feet and toes are fully developed. At this stage, the fetus begins to explore a bit, doing things like opening and closing its fists and mouth. Fingernails and toenails begin to develop and the outer ears are formed. The beginnings of the teeth form under the gums. The reproductive organs are also developing, but sex is still difficult to distinguish on ultrasound.

By the end of the third month, the fetus is fully formed. All organs and limbs (limbs) are in place and will evolve to become functional. The circulatory and urinary systems also function, and the liver produces bile.

At the end of the third month, the fetus is about 4 inches long and weighs about 1 ounce.

Since the most critical development has taken place, your chancemiscarriagedrops significantly after three months.

Second trimester

This middle part of pregnancy is often considered the best part of the experience. By this point, the morning sickness will likely have gone and the early pregnancy discomforts will have subsided. The fetus begins to develop facial features this month. You may also begin to feel movements as the fetus twists and turns in the uterus. During this trimester, many people learn whether their baby will be identified as male or female at birth. This is usually done during an anatomy scan (an ultrasound that checks physical development) at around 20 weeks.

Month 4 (weeks 13 to 16)

The fetal heartbeat can now be heard through an instrument called a doppler. The fingers and toes are well defined. Eyelids, eyebrows, eyelashes, nails and hair are shaped. Teeth and bones become denser. The fetus can even suck its thumb, yawn, stretch, and grimace.

The nervous system begins to function. The reproductive organs and genitals are now fully developed and your doctor can see furtherUltrasonicwhether the fetus is identified as male or female at birth.

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At the end of the fourth month, the fetus is about 6 inches long and weighs about 4 ounces.

Month 5 (weeks 17 to 20)

At this stage you can feel the fetus moving. The fetus develops and exercises muscles. This initial movement is called acceleration and can feel like a flutter.

Hair begins to grow on the head. The shoulders, back and temples are covered with a soft, fine hair called lanugo. This hair protects the fetus and is usually shed by the end of your baby's first week of life.

The skin is covered with a whitish coating called cheese grease. It is believed that this "cheesy" substance protects the fetal skin from the long exposure of the amniotic fluid. This covering is shed shortly before birth.

At the end of the fifth month, the fetus is about 10 inches long and weighs between 1/2 and 1 pound.

Month 6 (weeks 21 to 24)

If you could look inside the uterus now, you would see that the fetus's skin is reddish in color, wrinkled, and veins are visible through the translucent skin. The fingerprints and toe prints are visible. At this stage, the eyelids begin to open and the eyes open.

The fetus responds to sounds by moving or increasing the heart rate. You may notice jerky movements when the fetus hiccups.

Ifborn too early, your baby may survive after 23 weeks with intensive care.

At the end of the sixth month, the fetus is about 12 inches long and weighs about 2 pounds.

Month 7 (weeks 25 to 28)

The fetus continues to mature and develop body fat reserves. At this point, hearing is fully developed. The fetus frequently changes position and responds to stimuli such as sound, pain, and light. The amniotic fluid begins to decrease.

If born prematurely, your baby will likely survive after the seventh month.

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At the end of the seventh month, the fetus is about 14 inches long and weighs between 2 and 4 pounds.

Third trimester

This is the last part of your pregnancy. You might be tempted to start the countdown to your due date and hope it comes sooner, but each week of this final stage of development helps the fetus prepare for birth. During the third trimester, the fetus gains weight rapidly and adds body fat, which helps after childbirth.

Remember, even though popular culture only mentions nine months of pregnancy, you can actually be pregnant for 10 months. The typical full-term pregnancy lasts 40 weeks, which can take you up to a tenth month. It's also possible that you may miss your due date by a week or two (41 or 42 weeks). Your healthcare provider will monitor you closely as you approach your due date. If you are past your due date and not in labor spontaneously, your provider can arrange for you. This means medication is used to induce you to go into labor and have the baby. Be sure to talk to your doctor about your birth plan during this trimester.

Month 8 (weeks 29 to 32)

The fetus continues to mature and develop body fat reserves. You may notice more kicks. The brain is developing rapidly at this point, and the fetus can see and hear. Most internal systems are well developed, but the lungs may be immature.

The fetus is about 18 inches long and weighs up to 5 pounds.

Month 9 (weeks 33 to 36)

During this phase, the fetus continues to grow and mature. The lungs are almost fully developed at this point.

The fetus has coordinated reflexes and can blink, close its eyes, turn its head, grip tightly, and respond to sound, light, and touch.

The fetus is about 17 to 19 inches long and weighs between 5 ½ pounds and 6 ½ pounds.

Month 10 (weeks 37 to 40)

In this last month you could go inWorkat any time. You may find that there is less movement as space is at a premium. By this time, the position of the fetus may have changed to prepare for birth. Ideally, it is upside down in your uterus. You may feel very uncomfortable during this last period of time as the fetus falls into your pelvis and prepares for birth.

At this point, your baby is ready to face the world. They are about 18 to 20 inches long and weigh about 7 pounds.


What are the developmental stages of fetus during pregnancy? ›

The process of prenatal development occurs in three main stages. The first two weeks after conception are known as the germinal stage, the third through the eighth week is known as the embryonic period, and the time from the ninth week until birth is known as the fetal period.

What month is a fetus fully developed? ›

Thirty-one weeks into your pregnancy, or 29 weeks after conception, your baby has finished most of his or her major development.

What are the most critical weeks of fetal development? ›

First Trimester (0 to 13 Weeks)

The first trimester is the most crucial to your baby's development. During this period, your baby's body structure and organ systems develop. Most miscarriages and birth defects occur during this period. Your body also undergoes major changes during the first trimester.

What happens in each trimester of fetal development? ›

In the first trimester, your baby will grow from a fertilized egg into a moving fetus with eyes, ears, and working organs. In the second trimester, your baby's features develop and you may be able to feel your baby move. In the third trimester, your baby will grow rapidly to get ready for birth.

When does the soul enter the fetus? ›

The dominant theory is that the soul enters at conception. Some teach that the soul does not enter the fetus until 40 days after conception. All Jewish and Christian and Muslim teachings affirm that the fetus has a soul long before birth.

What is the last organ to develop in a fetus? ›

The lungs are the last major organ to finish developing. When fully mature, they produce a chemical that affects the hormones in your body.

What is the first organ to develop in a fetus? ›

The first organ system to develop during organogenesis is the cardiovascular system. The heart has established its four chambers by four weeks of development, whereas week six involves cardiac outflow separation and descent of the heart (and lungs) into the thorax.

What develops first heart or brain? ›

Thus, the first organ system to develop is the heart, blood and circulatory system, so that nutrients and waste can be transported throughout the growing embryo.

How early can you tell birth defects? ›

First trimester screening is a combination of tests completed between weeks 11 and 13 of pregnancy. It is used to look for certain birth defects related to the baby's heart or chromosomal disorders, such as Down syndrome. This screen includes a maternal blood test and an ultrasound.

What fruit is not good for pregnancy? ›

Fruits to Avoid During Pregnancy Diet
  • Papaya – It tops the list for obvious reasons. ...
  • Pineapple – These are also not recommended to the pregnant women as they contain certain enzymes that alters the texture of cervix which could induce premature contractions. ...
  • Grapes –

During which trimester is the fetus at greatest risk of malformations? ›

Harmful exposures during the first trimester have the greatest chance of causing major birth defects. This is because many important developmental changes take place during this time. The major structures of the body form in the first trimester. These include the spine, head, arms and legs.

What are the most important weeks of fetal development and why? ›

The fetus is most vulnerable during the first 12 weeks. During this period of time, all of the major organs and body systems are forming and can be damaged if the fetus is exposed to drugs, infectious agents, radiation, certain medications, tobacco and toxic substances.

What does a fetus look like at 8 weeks? ›

So what does a baby look like at 8 weeks? Baby's arms, legs, fingers and toes are all becoming more defined, and baby is less curled up, so you can see their constant little twitches and bounces. There is now an identifiable nose and upper lip, and wee little eyelids and ears.

When does the heart start beating? ›

By 22 days after fertilization, the heart starts beating. The heart beats about 54 million times between conception and birth. How many times has your heart beat? Doctors use a variety of methods to listen to the fetal heartbeat.

What is quickening? ›

Quickening is when a pregnant person starts to feel their baby's movement in their uterus (womb). It feels like flutters, bubbles or tiny pulses. Quickening happens around 16 to 20 weeks in pregnancy, but some people may feel it sooner or later. Appointments 216.444.6601.

Where does the soul reside in the human body? ›

The soul or atman, credited with the ability to enliven the body, was located by ancient anatomists and philosophers in the lungs or heart, in the pineal gland (Descartes), and generally in the brain.

What are the 4 stages of embryonic development? ›

  • Blastocyst Development. Soon after fertilization, the embryo is created from a small group of cells that are constantly dividing inside of a complex structure called the blastocyst. ...
  • Blastocyst Implantation. ...
  • Embryo Development. ...
  • Fetal Development.

What are the 4 stages of a fetus? ›

The development of a newborn during pregnancy is an amazing process. There are 4 stages of the pregnancy timeline including: 1st trimester, 2nd trimester, 3rdtrimester & birth.

What are the 5 stages of pregnancy? ›

  • Conception & implantation.
  • First trimester, weeks 1-12.
  • Second trimester, weeks 13-27.
  • Third trimester, weeks 28-40.
  • Fourth trimester, post-birth.
  • Additional resources.
May 10, 2022


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