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Gestational age: 8 weeks and 0 days until 8 weeks and 6 days old. 57–63 days from last menstruation. Embryonic age: Week nr 7. 6 weeks old. 43–49 days from fertilization. The embryo measures 18 mm (3 ⁄ 4 in) in length. Fetal heart tone (the sound of the heart beat) can be heard using doppler. Nipples and hair follicles begin to form.
The normal period of gestation (pregnancy) is about nine months or 36 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days. [1] During this stage, the zygote divides in a process called cleavage.
The development of the human embryo follows fertilization, and continues as fetal development. By the end of the tenth week of gestational age, the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many organs become fully developed.
The American Library Association regards it, alongside Gray's Anatomy, as a core medical reference work for libraries. [13] The book was often cited as presenting the first images of a live fetus in utero. [14] In fact, Geraldine Flanagan's The First Nine Months Of Life had in 1962 compiled a similar set of fetal images from medical archives. [15]
Babies born between 39 and 41 weeks' gestation have better outcomes than babies born either before or after this range. [63] This special time period is called "full term". [63] Whenever possible, waiting for labor to begin on its own in this time period is best for the health of the mother and baby. [17]
Complete expulsion of the baby signals the successful completion of the second stage of labour. Some babies, especially preterm infants, are born covered with a waxy or cheese-like white substance called vernix. It is thought to have some protective roles during fetal development and for a few hours after birth.
According to Dr. Nathan Sundgren, associate medical director of the neonatal intensive care unit (NICU) who treated the babies, the sisters are now all between 6.5 to 7 pounds, and "doing great."
The vision of infants under one month of age ranges from 6/240 to 6/60 (20/800 to 20/200). [4] By two months, visual acuity improves to 6/45 (20/150). By four months, acuity improves by a factor of 2 – calculated to be 6/18 (20/60) vision. As the infant grows, the acuity reaches the healthy adult standard of 6/6 (20/20) at six months. [5]