Human embryo and fetal development: Pregnancy Stages
Whether you are trying to conceive, already pregnant or are considering it, the fact is that everyone is very curious and wants to know how the fetus develops while in the womb. It is a natural curiosity for anyone to wonder, and for centuries it was a question that stumped us all. Thanks to modern medical research and good old Scientific studies, we now are able to understand this miraculousness that occurs within the womb. Pregnancy happens in three stages of development. The first, second and third trimesters. below we will go over each trimester for you broken down into weeks.
First Trimester: The most crucial time for an embryo’s development and nutritional needs.
Weeks One through Three: During the first week you should be expecting the arrival of Aunt Flow (your period). In this time you are not actually pregnant yet. At the beginning of week two the estrogen in your body will send a signal to your uterus, letting it know that your body is ready to begin to support a fertilized egg. While all of this is going on, your ovaries are harvesting their eggs into fluid filled sacs called follicles. Week Three entails your ovaries release of these eggs into your fallopian tubes. Ovulation occurs around mid cycle. This is usually between day 13 and 16 of a normal 28 day cycle. Once in the fallopian tubes an egg has to be fertilized within twelve to twenty-four hours or else the egg will be absorbed back into the lining of your uterus. After fertilization occurs the now ‘fertile’ egg is referred to as a zygote*. It is at this time after the sperm has successfully made its way into the zygote that it immediately hardens its outside so that no other sperm can penetrate it. You will not be able to tell that you are pregnant for at least a few more weeks.
Weeks Four through Seven: At the beginning of this week you may notice that your period is now late. Pregnancy can easily be determined by taking a home pregnancy test and confirming the results with you physician. If the test results are positive, make an initial appointment with your Doctor and discuss with him any medications you are currently taking and the importance of prenatal nutrition. Remember that the next six weeks are very critical to you baby’s development. It is around this time that most women are very anxious and are wondering what is going on in the womb. At this point, the cells that form the zygote, now called a blastocyst* is rapidly multiplying. At the end of its trip down your fallopian tubes it will snuggle itself up against your Uterine wall and divide into two parts. One part will become the baby, while the other will attach itself to your Uterus and become the placenta. The little cluster of cells that is now forming your baby is about the size of an apple seed, and by the end of the Fifth Week will be about a half an inch long. Your baby much resembles that of a pollywog rather than anything human. It now has a heart that pumps blood and some of its limbs will begin to sprout soon. By Week Seven your baby is the size of a grape and almost three quarters of an inch long. Her toes are distinctly webbed and she jumps around your uterus like a Mexican jumping bean.
Weeks Eight through Twelve: From this point to about twenty weeks your baby will go through a major growth spurt and begin to develop more rapidly. Your baby’s veins are clearly visible and her brain is now functioning. It may become harder for you to keep most foods down because of the nausea, and bathroom trips may become more frequent. You may find that your mood varies throughout the day. You may feel happy and excited one minute and depressed and overwhelmed the next. Your breasts will also start to change, getting bigger and more sore as the weeks pass. As your waist starts to get thicker you may need to buy bigger clothes to accommodate your growing body. At about nine weeks your baby is now called a Fetus, is about one inch in length and much resembles a lima bean. Even though you cannot yet tell what the sex of your baby is, the genitals are now beginning to form. At ten weeks you can hear your baby’s heartbeat and see your baby on an ultrasound, and at about 12 weeks your worries of miscarriage are over and greatly reduced. Your Uterus will now be well above your pubic bone and felt during an exam. Your baby is now beginning to look more human. her ears are beginning to move into their correct places and her kidney’s are secreting urine into her bladder.
Second Trimester: A stage of tremendous growth and Development
Weeks Thirteen through Sixteen: Your fetus is now about three to four inches long from head to bum and weighs a little more than a half an ounce. Your baby is responsive to noise and touch. The noise she hears sounds much like an echo though. When you touch your belly she can feel it and begins to search, as if looking for a nipple. You should start to feel some relief within the next couple weeks. Your nausea, frequent urination and tiredness will subside and you will begin to feel much better. At about 14 weeks eyebrows form, and your baby can now suck her own thumb. This would be about the time for a multitude of tests to screen for any abnormalities in your baby’s development. Fifteen weeks in, you may find that you have probably gained about five to ten pounds. Your baby’s legs are continuing to grow and you can now have an ultrasound to determine your baby’s sex. By the time you reach your Sixteenth week, your baby is now the size of a medium sized apple. In the coming weeks she will grow rapidly and nearly double her weight and length.
Weeks Seventeen through Twenty: Your baby’s skeletal system mostly resembles that of cartilage, like you would find in your ear or nose. This will begin to harden to form a more permanent skeleton. Right about now your Doctor may schedule an appointment for a mid pregnancy ultrasound. These are used to monitor fetal development, screen for any birth defects and to assess the baby’s gestational age. Be expectant for your baby to kick, turn, reach or even suck on her thumb. It is now the Nineteenth week of development and your uterus has now risen to your bellybutton. It will continue to grow about a centimeter a week. A whitish jacket of a fat like substance called Vernix Caseosa* forms around your baby and acts as a shield, protecting the skin from the amniotic fluid. Now would be a great time to start looking for child birthing and education classes. It is crucial for your body to get a full amount of iron in a day. Remember, you are eating for two!
Weeks Twenty-one through Twenty-four: Your baby is now about twelve ounces and ten inches in length. Her eyelids are fully formed and she now has fingernails. Your baby can now hear everything on the outside. Some studies show that reading to your child while in the womb helps to soothe and relax them. By week Twenty-three her eyes, mouth and nose are formed. It is likely that you have gained a little more than ten to fifteen pounds by now. Speaking of gaining weight, you baby now weighs just over a pound. In addition to this, you baby’s major blood vessels and lungs are developing in order to prepare her for her first breath. If born now, though very premature, your baby would have a chance of survival if given the proper medical care. At the end of week Twenty-four she will weigh almost a pound and a half. You will start to notice that you have faint red lines on your stomach, buttocks, thighs and waist (stretch marks). Don’t panic they will fade after delivery.
Third Trimester: Weight gain Galore
Weeks Twenty-five through Twenty-eight: Your baby now weighs two whole pounds. She is able to open and close her eyelids and now sleeps pretty regularly. Any movement from baby is most likely caused by hiccups. You yourself may find it harder to breath now that your uterus is up by your rib cage. Your baby now weighs two and a half pounds and is nearly 15 inches long. She can now turn her head and can notice a bright light shinning in from the outside. Be prepared to gain about eleven more pounds by your week Forty.
Weeks Twenty-nine through Thirty-two: Whoa Nelly! You baby’s head is getting bigger and her brain growth is getting more rapid. Be sure to get plenty of protein, folic acid, Vitamin C and Iron during this time, it is crucial for your baby’s nutritional needs. While her lungs and digestive tract are almost fully formed her growth may begin to taper, but she will still gain weight. Little fuzzy hairs are now present for eyebrows and lashes. Around two to four weeks prior to delivery your baby’s head will drop into place making it much easier for you to take a breath. The rest of her body starts to fill out and finally is in proportion with the rest of her body. She is secreting water from her bladder. You will continue to gain weight at about a pound a week for the rest of your pregnancy.
Weeks Thirty-three through Thirty-six: Four and a half pounds and seventeen inches long sounds about right. In these weeks your Doctor will be monitor you closely to watch the baby’s position. Your baby’s head is not fully formed so that it will make easing out of the birth canal much easier. For first time mothers expect your baby to move into position and her head to put pressure on your cervix. If you are having sore or swollen ankles try to drink more and keep hydrated, this reduces water retention. If you are beginning to wonder and get nervous about going into labor early, calm down. Babies born at this stage can survive outside the womb having little or no problems. Week 35 brings your baby’s weight to 5 and a half lbs. and nearly 19 inches long. On average you have probably gained between 25 and 35 lbs. Continue to drink plenty of water, but be sure to stay away from diuretics that will make you have to urinate more often. You may begin to feel a fullness in you lower abdomen and feel like your going to drop her right out. This is not the case, your baby is just moving herself into position. But good news is near, at the end of this week, you are considered full term. Your baby now weighs between 5 and 6 lbs and is approximately 19 inches long.
Weeks Thirty-seven through Forty: Expect you baby to weigh between 5 and 7 lbs about now. She will most likely have a full head of hair. If your wondering about the color of your baby’s eyes you may not be able to tell right away. Although most baby’s born with brown eyes stay brown, you will not know for sure until she is about 9 months old. At the time of birth most baby’s weigh between 6 and a half to 7 and a half lbs. and are from 21 to 23 inches in length. The amniotic fluid surrounding your baby is now a pale pinkish color. The lining of the Vernix Caseosa is shedding and your baby will swallow this and it will become its first stool, known as Meconium*. In some women (less than 15%) your water can rupture unexpectedly, but don’t panic, that little baby of yours is holding steady like the cork on your favorite wine. If this happens call your Doctor and make your way to the hospital. If your water has not broken by now, don’t panic. Your Doctor will want to wait a week or two to see what happens and if nothing does they may break your water and induce your labor.
Hope you have a happy and gleeful pregnancy!
- Zygote: The result of when an egg and sperm meet.
- Blastocyst: Fluid filled clusters of cells
- Vernix Caseosa: Fatty like substance that protects a fetus from amniotic fluids during pregnancy. Usually develops during the second trimester. Also eases labor.
- Meconium: A greenish black, sticky like substance that passes as your baby’s first stool. It is made up of goo swallowed by the baby when in the womb (lanugo hair, Vernix Caseosa, and amniotic fluids).