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What Are the Stages of Fetal Development?

By O. Wallace
Updated Mar 03, 2024
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A baby undergoes rapid fetal development in the nine months he spends in his mother’s womb. A pregnancy is usually measured in 40 weeks of gestation, but many people prefer to measure it in months. The three main stages of development are ovulation/conception, embryonic development and development of the fetus.

Ovulation usually occurs around week two of the cycle. In the two weeks prior to conception, the body is readying the womb for a potential pregnancy by growing a layer of rich, blood perfused tissue. After conception, which takes place about two weeks into the cycle, the egg makes its way to the uterus, where it is implanted and begins its rapid growth.

Embryonic Development is the most critical stage of fetal development, when the systems are undergoing important foundational development. The embryonic state of development takes place from conception to approximately the 11th week of pregnancy. After the second week, the development of the embryo is in full swing. At four weeks, cellular division continues, with the cells dividing between the those that will make up the placenta and those that will make up the baby.

By six weeks, the baby’s heartbeat has begun and her arms and legs are developing. At eight weeks, the intestines begin to form and teeth start growing under the gums. By the end of the embryonic stage of fetal development, the embryo has developed joints and the beginning of the irises. Major organs have begun their development, as well as the central nervous system.

Fetal Development begins after the 11th week, when the baby is called a fetus. From the 11th to 16th week, the fetus begins developing distinguishable genitals, hair, nails and vocal chords. The kidneys begin to process bodily fluids, and the liver begins to function as it should. Bones also begin to harden at this time.

From the 16th to 20th week, the baby undergoes another rapid growth spurt. He begins to develop fat under a thin skin. The heart pumps a staggering 25 quarts of blood every day. Meconium, a baby’s waste product, accumulates in the bowel. The fetus regularly hiccups and spends the same amount of time awake and asleep as a typical newborn.

Fetal development slows down during the 21st to 24th weeks. The eyelids and eyebrows are usually completely formed by this time, and if the fetus is a boy, his testes begin to descend from the pelvis. By the 24th week, the baby will weigh approximately 1.3 pounds (.6 kilograms).

During the period of time from the 25th to the 28th week, the baby continues to develop. Lung development is marked during this time, as the baby prepares to breathe air at birth. By the 28th week, 90% of babies born will survive, although breathing may be an issue. The lungs begin to secrete surfactant, which is necessary for breathing. Ligaments form, nostrils open and brain development proceeds at a fast rate. The baby’s retinas begin to form, and she can completely open her eyes at this point.

From the 29th to the 40th week, fetal development is focused on the development of the lungs. For the most part, all of the major systems and organs are complete. The baby’s job is to fatten up to face the environment outside of the protective womb. The baby begins to develop immunities needed to survive. At 37 weeks, the baby will continue to add approximately one ounce (28.35 grams) per day to his body weight. This week marks a pregnancy as full term, and the baby should be delivered with no complications.

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Discussion Comments
By anon286163 — On Aug 20, 2012

@anon136362: If a baby is born with a hole in its heart, or due to a flaw in gene expression, the baby's lungs do not develop correctly, or due to incomplete development of the limbs the baby is born without arms, or the mother miscarries at six weeks, what does that say about your incredible and ultra intelligent god then?

The truth is, you are seeing connections where they do not exist. Our evolutionary history is written into our embryos, the same as it is written into every vertebrate embryo. Human embryos share the same characteristics with all vertebrates.

From the beginning of embryonic development to about 41 days or so, the embryo develops a full grown tale and also possesses gill slits which hail back to our fish and monkey ancestors (Monkey-like to be more appropriate, our common ancestor with apes). The gill slits develop into what will become the lung tissue (Coincidental?). The tail, due to programmed cell death disappears leaving only the coccyx (our vestigial tail). Yet the tail is only physically gone; however the genes that caused it to form in the first place are still written into the genetic code in a dormant state.

Our genetic code in and of itself is also far from unique. We share over 99 percent of our gene sequence with chimps and the same four proteins -- adenine, guanine, cytosine, and thymine -- are used to form the DNA sequences for every single living creature on Earth which again only highlights our common ancestry with all other species.

It does the human race no good to cling to beliefs written in a 3,000 year old book that was penned by men who believed that the earth was flat and had four corners (Job 38:13, Daniel 4:7-8), or that the reason we have so many different languages is because god was scared that humans were going to build a tower that could reach him (Genesis 11:1-9); who believed the Sun and Moon were made to stand still in the sky for 24 hours (Joshua 10:12-14). They believed this because they thought the Earth was the center of the universe). The Bible is not a science textbook and your interpretation of scripture as mystically being connected to the phases of human embryological development is closer to pagan numerology than to Christian beliefs.

However, if your comment was intended to display why it is wrong for a woman to choose to have an abortion if the child is unwanted, illegitimate, or the product of sexual assault, then please consult 2nd Samuel chapter 12 for God's position on abortion.

Despite David's fasting and praying to God to allow his child with Bathsheba to live, God kills the child for David's sin! Keep in mind this was a fully developed child, a fully born human being. And not only did God kill the child, but he made the child suffer for several days before finally allowing it to die. When the child dies, David stops fasting and praying, goes and has some lunch and then goes and has sex with Bathsheba again. This time because she is his wife now God doesn't get mad and he gives David and Bathsheba a son, the wise King Solomon, to make up for the dead kid (who by the way, was never even given a name).

This is the Bible's stance on baby killing! This is the nonsense that people who follow the Bible never bother to pay attention to. Next time someone tells you that baby killers and pro-choicer are going to hell, read them 2 Samuel chapter 12. What "an incredible, powerful and ultra-intelligent God!" Yeah, right!

By anon259823 — On Apr 08, 2012

In what way is that evidence of anything other than coincidence?

Evidence is fact based. Not vague number comparisons.

By anon140838 — On Jan 08, 2011

Amen to what anon136362 said. I completely and utterly agree.

By anon136362 — On Dec 22, 2010

To Anon67569: the number three is indeed God's special number! It's found through the whole Holy Bible (thousands of years before the Quran even existed), and the number three represents God's Holy Trinity: Father, Son and Holy Spirit. The baby's three stages are a representation of God our creator at work.

Not only that, but there are also 40 weeks of pregnancy (The number 40 means in the Bible a breakthrough or finalizing something), and by six weeks the baby's heart has begun pumping (God created man on the sixth day )!

All of this evidence just gives more proof to the existence of an incredible, powerful and ultra-intelligent God!

By anon67569 — On Feb 25, 2010

The holy book Quran which is over 1500 years old has a verse saying "God who created you in three stages in the womb".

Who else would know this some 1500 years ago? I'm pretty sure there were no ultrasound machines back then.

By anon37128 — On Jul 17, 2009

there is actually another stage called the Germinal stage that goes from conception to the end of the 2nd week and embryonic then follows

By bigmetal — On Feb 21, 2008

it is so exciting, tracking the development of your child! i'd suggest subscribing to an online calendar of fetal development, which sends you an email everyday with a new tidbit about what's going on with you and/or your baby. you find out all types of interesting stuff, get tips on what you should be eating, advice on preparing for the baby, etc. send it to your husband too, because men often aren't as connected to what's going on with you and your baby otherwise!

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