Conception to Fetus
Although a pregnancy starts as soon as fertilization occurs, it is at the ninth week that the baby growing inside is referred to as a fetus. Before this time, the fetus has been referred to as a blastocyst, zygote, morulla and embryo. The period between conception and the ninth week is the most critical period during a pregnancy. The fertilized egg travels down the fallopian tube and implants into the uterus wall. After dividing and multiplying hundreds of times, the mass that will become the body begins to divide into sections that will make up the head, limbs and internal organs. Most importantly, during this time the heart forms and begins beating.
Ninth to 20th Week
At the ninth week of pregnancy, the fetus is around 25 mm long and is starting to develop the internal organs. His wrists can bend and he now has eyelids that cover his eyes. The presence of ears are starting to appear on each side of the fetus' head. The genitals are also forming; although it is too early to determine if you are having a boy or girl.
From the 10th week to the 20th week, the fetus continues to grow at an astonishing rate. The fetus goes from 1 1/2 inches to 9 inches and weighs around 8 oz. at the end of the 20th week. During this time, the genitals have formed and so have the internal organs. The fetus' body is starting to produce hormones. The placenta has started to operate and the fetus is now circulating it's own blood. The fetus now has a facial profile and the bones have started to harden. The vocal cords have started to develop and he is now excreting urine every 45 minutes.
By the 20th week, the genitals are visible and a physician can determine the sex of the fetus via an ultrasound.
21st to 40th Week
Around the 21st week, the fetus will weigh approximately 1 lb. The fetus can hear your voice. The fetus is extremely active and its movement can be felt several times a day.
Between the 22nd and 30th week, the fetus is continuing to grow and develop the needed body functions to survive. His skin is wrinkled and the nostrils are beginning to open. The fetus now has her own set of fingerprints and is learning the voice of her parents.
By the end of the 30th week, the fetus weighs close to 3 lbs. and is around 14 inches long. He can now recognize the difference between light and dark and has developed a sleep pattern.
During the 31st to 40th week, the fetus continues to develop and mature. The main change that occurs during this time is that the fetus will start storing fat. The body will be able to adapt to temperature changes and the bones will be fully formed. Although the bones are still able to move slightly, they are strong and can withstand the force of delivery. By the end of the 37th week, the fetus is now fully developed, weighs 7 to 8 lbs. and can survive without assistance if born now.
References
- Pregnancy and Giving Birth
- Taking Charge of Your Fertility; 2006; Toni Weschler
