The Stages Of Pregnancy Development From Inception To Delivery

It is shocking how most pregnant women still have a blurry understanding of how their baby evolves throughout their pregnancy.

Pshhh, and I get it! Science isn’t everyone’s favorite subject. Moreover, you can just bear the child for nine months.

But it is much more than just that.

It is also about your well-being because your body will change as the pregnancy progresses through each stage.

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You will experience a rollercoaster of physical and emotional changes.

I’m talking about morning sickness, hormonal changes, and how your body craves prenatal vitamins to assist your baby.

Nurturing a fully-formed baby, the baby’s first movements (quickening), prenatal bonding activities, and preparing for labor—all of these crucial phases of motherhood you could miss out on.

This is why it is imperative to have comprehensive knowledge of pregnancy development to know what to expect and how to properly care for yourself and your baby until delivery.

Exploring The Stages of Pregnancy Development from Inception to Delivery

Stages of Pregnancy Development
Image Source: iStockphoto/Nadezhda Deineka

In this section, we will take a steep dive into each trimester, discussing the stages of pregnancy development month-by-month, weeks-by-weeks—from inception to delivery.

So, without wasting much of your time, let’s surf into the first trimester, where it all begins.

Stage 1: First Trimester

Stages Of Pregnancy Development - First Trimester

The first trimester is the first three months of your pregnancy, from conception to implantation, which is broken down into 12 weeks.

It tells us how the fertilized egg slowly changes from a small grouping of cells to a fetus that begins to sculpt human features.

You could start experiencing early pregnancy symptoms such as morning sickness, increased urination, swollen breasts, and fatigue.

But most women do at the latter stage of their pregnancy.

So what happens in month 1?

Month 1 (From Weeks 1 To 4)

If you have not yet hit your menopause benchmark, you ovulate once every month –usually about 14 days after the last period—which is week 2.

This is a period when the ovary deploys the egg (ovum) into the usual site of fertilization: the fallopian tubes.

This is your fertile window—when you are most likely to get pregnant—because the mucus in the cervix tends to be more fluid and elastic.

This then creates a paved passage for traveling sperms to the uterus faster, with a waiting egg in the funnel-shaped end of a fallopian tube to be fertilized.

Week 3

Having unprotected sex within five days before ovulation or on the day of ovulation often leads to fertilization.

Fertilization typically happens during week 3 when sperm and egg unite to form a zygote.

Week 4

By the time the zygote travels down the fallopian tube to become a morula, the morula becomes a blastocyst once it reaches the uterus; it is week 4.

Then, the blastocyst burrows into the uterine wall—a process called implantation.

An amniotic sac (a water-tight sac) forms around the blastocyst as a cushioning for a fetus during pregnancy.

The blastocyst becomes 2 millimeters (mm) long by the end of the fourth week.

Month 2 (From Weeks 5 To 8)

Most women realize they are pregnant in the second month of the pregnancy.

They miss their period, hormones fire up, and they end up conducting a home pregnancy test that shows positive.

It is at this latter stage most women start experiencing pregnancy symptoms.

Week 5

The embryo continuously elongates, hinting at a human shape, and the neural tube (the brain, spinal cord, and other neural tissue) gradually develops.

Week 6

The heart and major blood vessels start taking shape after that. Circulation begins. First, the heart pumps fluid through the blood vessels before the first red blood cells appear.

The blood vessels keep developing in the embryo and placenta at this juncture. Structures sprout to be eyes, mouth, and ears begin to take form.

Week 7

Soft cartilage grows to be bones, and genitals slowly form. At this stage, the embryo resembles a tiny tadpole or seahorse because of its tail.

But this tail later becomes the leg and the large head shapes, respectively.

Week 8

The major organs and body systems are still developing, with the fetus having web-like hands and feet.

However, the umbilical cord is mature enough to help deliver blood and oxygen to the embryo.

At the end of the 8th week, the embryo becomes a fetus about 0.5 to 1 inch long, about the size of a black bean.

Month 3 (From Weeks 9 To 12)

Week 9

By week 9, the fetus takes on more of a human form by developing muscles. However, the head is still 50% of its length.

But the fetus is growing teeth and taste buds.  

NOTE: Most congenital disabilities occur at this stage, considering the embryo is vulnerable and still developing.

It is susceptible to the effects of radiation, viruses, and even drugs.

It is why pregnant women don’t take live-virus vaccinations or any drugs at this period unless it is prescribed by a pharmacist or considered to be helpful to their health.

Week 10

The sprouted arms with webbed fingers are fully formed. The arms, hands, fingers, and feet are more visual, with fingernails and toenails slowly coming up.

The external ears and genitals continue to form.

Week 11

The bones are reinforced, but the skin isn’t.

The fetus can now make tiny movements, such as opening and closing its mouth and fists. The ankles, knees, and elbows are fully functional but are not quickening yet.

The facial features are also noticeable.

Week 12

Week 12, most women are relieved from the morning sickness.

The fetus might have grown to the size of a plum –about 2.5 to 3 inches long –with all limbs, bones, muscles, and organs complete but still under-developed to be fully operational.

The good news is that since most of the critical development has occurred, miscarriage is less likely to happen.

Stage 2: Second Trimester

Stages Of Pregnancy Development - Second Trimester

The 13th week is the beginning of the second trimester, when the symptoms and discomforts of early pregnancy must have died down.

At this stage, you can feel your baby’s movement as it flips and turns in your uterus.

Your maternity care provider can now dictate the fetal heartbeat on a Doppler ultrasound loud and clear and discover your baby’s assigned sex.

Month 4 (From Weeks 13 To 16)

Week 13

By now, your baby weighs about 1 ounce and is 3 inches long, with the large head growing proportionate to its body.

Week 14

The fetus’s skin thickens a bit, with fine hair sprouting underneath. Fingers start drawing closer to its mouth and can make a couple of head moments.

External genitals are also developed with fingerprints emerging bit by bit.

Week 15

The intestines, ears, and other organs begin to migrate to their permanent location. However, the fetus still uses amniotic, as its lungs are still developing.

Baby can make purposeful movements such as facials and sucking of thumb.

Week 16

By week 16, your baby has developed enough to hear you talk. It can react to light by veering away even with its eyes closed.

At the end of the 4th month, the fetus is as big as an avocado –about 5 inches long and weighs about 4 ounces.

Month 5 (From Weeks 17 To 20)

At this time, most women feel their baby is quickening and get their first ultrasound checked for the fetus’s assigned sex.

Week 17

The fetus starts putting on fat on its thin skin covered with vernix (a whitish cheesy coating) that shields it against prolonged amniotic fluid.

Week 18

The fetus is still under the coverage of lanugo (a peach fuzz-like hair) that helps keep it warm while providing an extra layer of protection.

Note that loud noises may wake your baby up at this point if it is asleep, thus affecting its sleep cycle.

Week 19 to 20

The fetus can hiccup and begin kicking and punching as it’s become much more potent with its fully developed fingers and fingerprints.

By the end of the 20th week, your baby must have grown 9 to 10 inches long and weigh about 1 pound.

Month 6 (From Weeks 21 To 24)

If you could peek through the uterus, the fetus has reddish, wrinkled, translucent skin with showy veins.

Your baby makes more jerky movements and increases its pulse in response to sounds. And the eyelids begin to part.

Week 21

The development of bone marrow has taken place to help produce blood cells. The movement of the limb is much coordinated and frequent.

Week 22 to 23

Your baby can hear your heartbeat, breathing, and stomach rumbling. Its grasp is much firmer and can reach for its ears.

Fats add up more rapidly, making the skin less wrinkled and plumper. The nervous system is maturing. The fetus can survive under intensive care if born prematurely at this stage.

Week 24

The fetus must have grown to 12 inches long and weighs about 2 pounds, with fully emerged lungs—though not enough to function independently outside your uterus.

Stage 3: Third Trimester

Stages Of Pregnancy Development - Third Trimester

The third trimester is the final stage of your pregnancy, which helps the fetus prepare for birth; it gains weight more rapidly.

Count down the start as you approach your due date. Your healthcare provider monitors you closely as you visit biweekly and then weekly.

Month 7 (From Weeks 25 To 28)

The fetus makes melanin at this stage, giving the skin and eyes their color. The lungs make surfactants that assist with breathing.

In addition, your baby can open and blink its eyes with eyelashes.

At the end of the 7th month, the fetus must have grown to 15 inches long and weigh between two to three pounds.

It is also getting ready to turn head-down, preparing for birth, but keeps maturing.

Month 8 (From Weeks 29 To 32)

Week 29

Fetus’s brain is mainly developed and can respond to little stimuli. You will get more kicks and jabs—like poking since the fetus feels more cramped in the amniotic sac.

Week 30

Internal systems are advanced and can control body heat while the brain accelerates its growth.

Week 31

The fetus comprehends more information and stimuli because other organs are well-formed besides the lungs and brain.

You can notice when it’s awake or even asleep. But the pattern is subtle.

Week 32

Your baby has increased to approximately 17 to 18 inches long and weighs up to 5 pounds.

Month 9 (From Weeks 33 To 40)

The final weeks of the third trimester begin 35 to 38 weeks after conception.

However, in Week 33, the fetus’s bones are much stronger, but the brain remains soft to descend the birth canal.

The vernix that shields the skin becomes thicker in week 34, and the brain continues to grow until week 35, weighing only two-thirds of what should be at birth. 

But the fetus loses its lanugo and gains actual hair on its head. At 36, the fetus should be about 17 to 19 inches long, weighing 6 to 7 pounds.

The fetus’s organs are fully developed and prepared for birth in the coming weeks.

Weeks 37 to 38, anything can happen. The fetus changes position most suited for birth and drops down into your pelvis.

You can feel the pressure and discomfort at this final period; the doctor encourages you to kick count.

The fetus gathers 0.5 pounds per week to mature in size fully.

And by week 39 to 40, your baby is ready to meet the world.

It has grown to 18 to 20 inches long and weighs about 7 to 9 pounds, ripening enough to drop. Call your pregnancy care provider upon your first sign of labor.

Most women prefer to be in the hospital a few days before their due time.

And since this is the time when you need to start preparing for the hospital, it’s essential you already know what to pack in your baby’s hospital bag—whether it’s your first pregnancy or not.


Stages of Pregnancy Development
Image Source: iStockphoto/ONYXprj

I didn’t touch on all the finest details because I don’t want to bore you with the science.

However, this provides a comprehensive overview of the various stages of pregnancy development, from conception to delivery.

And before welcoming the arrival of your little miracle, you might have been briefed on the labor process, stages of labor (dilation, pushing), and pain management during childbirth for a successful delivery.

Do your utmost to cooperate with the doctor.

We wish you a successful delivery!

Stages of Development of the Fetus ( –
Implantation and Placentation ( –
Fetal Development ( –
What is prenatal development? ( –

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