Fetal Development

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Early Pregnancy

Fetal Development as Seen Via Ultrasound
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The egg and sperm meet in the outer third of the Fallopian Tube. Once they join the two cells begin to rapidly multiply. This stage of gestation is known as the zygotic stage and your baby is known as a zygote. From here the baby will become a blastocyst and implant in the uterine lining. The inner cells develop into the embryo while the outer cells will nourish your baby and become the amniotic sac and the placenta.

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4 Weeks of Pregnancy

Pregnancy Week 4
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Your baby is growing, but you're probably not even aware of it yet. This is why taking care of yourself prior to pregnancy is so vital to your baby's health.

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7 Week Fetus

Pregnancy Week 7
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The hand plates become present this week, and the baby is about 7-9 mm CRL by the end of the week. The genital tubercle is present, but you can't distinguish girls from boys by sight at this point. Nasal pits are forming.

Your baby will actually go through 3 sets of kidneys, very rapidly as they develop during this period. This week the second of such sets will form.

With a transvaginal ultrasound, one study shows that 100% of the ultrasounds will show a fetal pole with heart motion.

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8 Week Fetus

Pregnancy Week 8
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Your baby will be about 8-11 mm CR by the end of the week. The baby's hind brain is clearly visible. This week the baby's gonads will become either testes or ovaries. And spontaneous movement begins! There are a lot of things that we do know about life before birth.

Bones and joints this week have many things going on. Elbows appear and the process of ossification (hardening of the bones) begins. Toe rays become present, almost ready for you to count!

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10 Week Fetus

Pregnancy Week 10
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The baby now enters its fetal period. The average size is approximately 27-35 mm crown to rump length (CRL), or 1.06-1.38 inches. S/he weighs in at 4 grams, or 4 paper clips. Tiny toes have formed. The eyes are largely open, but the eyelids are beginning to fuse, and will stay that way until 25-27 weeks. External genitalia is beginning to differentiate. External ears are completely formed, as well as the upper lip. The biggest accomplishment this week is the disappearance of the tail!

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12 Week Fetus

Pregnancy Week 12
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While your baby's brain is not the same size it will be at birth, it does have the same structure. Bile is being secreted by this time. S/he weighs about 14 grams and is approximately 3.54 inches in total length.

Your baby has its reflexes and also practice movements in the digestive tract. All of this in preparation for extrauterine life.

If your practitioner uses a doppler, you may be able to hear your baby's heartbeat at this office visit. It will sound very fast. Some say that they hear clicking or the sounds of horse hooves. Either way, it is a joyous sound to hear! Your risk of miscarriage is greatly reduced once you hear this sound.

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16 Week Fetus

Fetal Development as Seen Via Ultrasound
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Your baby's nails are well formed, and some babies are even in need of having their nails trimmed at birth. The ears have also moved from the neck to the head.

Your baby is emptying his or her bladder every 40-45 minutes. The limb movements are becoming more coordinated. Your baby is about 3 ounces (85 grams) and 6.3 inches (16 cms). The sex of your baby may be detectable by ultrasound.

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24 Week Fetus

Pregnancy Week 25
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Your baby is almost completely formed and is beginning to deposit brown fat on his or her body. The purpose of the brown fat is to retain body heat. Newborns are notoriously bad at regulating body temperature at first. This is particularly a problem for a baby born early.

Babies born at this point have some chances of survival with very special care. They will be in the Neonatal Intensive Care Unit (NICU), probably for many weeks. Usually, we say that you can expect them to stay in the NICU until their due date.

A major problem with premature babies is lung development. If preterm labor is detected early enough a steroid shot, called Betamethasone, can sometimes be given to enhance lung development.

S/he weighs in at 1 lb 5 ounces (595 grams) and 30 cms or 11.8 inches total length!

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26-28 Week Fetus

Pregnancy Week 27
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At 26 weeks your baby's veins are visible through your baby's skin, although it is quickly changing from transparent to opaque.

Your baby can hear you and those around you. Although we assume that the uterus is a quiet place, the baby has been surrounded by noise for a long time. Things like your heart beat, digestion, and other body functions are heard by the baby as well as external noises. Now you may feel the baby jump at a sudden noise. My daughter would always jump when I clicked the bathtub lever. It became a game!

The uterus also allows some light to be seen. So your baby is aware of lightness and darkness.

S/he weighs 1 pound 12 ounces (794 grams) and measures 32.5 cms or 12.8 inches total length.

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30-32 Week Fetus

Pregnancy Week 31
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The baby is very aware of the surroundings. We tend to think of the uterus as a dark place. The uterus actually can be light and dark depending on the mother's environment. You may be able to distinguish sleep and wake cycles in your baby. Although it usually seems as if the baby wants to sleep while you are awake and vice versa at night. This is not indicative of a sleepless newborn.

If you are having Braxton Hicks Contractions use them to practice what you've learned in childbirth classes, and know that they are a sign that your body is getting ready for labor. The baby notices the contractions but is not adversely affected by them.

Your sweetpea weighs a whopping 3 pounds (1.36 kilograms)! S/he measures about 14.8 inches (37.5 cms) in length.

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