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Embryonic age: Week nr 1. 0 (whole) weeks old. 1–7 days from fertilization. Fertilization of the ovum to form a new human organism, the human zygote. (day 1 of fertilization [1]) The zygote undergoes mitotic cellular divisions, but does not increase in size. This mitosis is also known as cleavage.
Nine-week-old human embryo from an ectopic pregnancy. Organogenesis is the development of the organs that begins during the third to eighth week, and continues until birth. Sometimes full development, as in the lungs, continues after birth. Different organs take part in the development of the many organ systems of the body.
In human pregnancy, prenatal development is also called antenatal development. 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 ...
Photos of what pregnancy tissue from early abortions at 5 to 9 weeks looks like have gone viral. ... that “weeks 5 to 9 is the early time period in a pregnancy. At 5 weeks, the embryo is a mass ...
About 80% of miscarriages occur in the first 12 weeks of pregnancy. The underlying cause in about half of cases involves chromosomal abnormalities. [158] Stillbirth is defined as fetal death after 20 or 28 weeks of pregnancy, depending on the source. It results in a baby born without signs of life.
Human organs and organ systems develop in a process known as organogenesis. This begins in the third week of embryonic development, when the gastrula forms three distinct germ layers, the ectoderm, mesoderm and endoderm. The ectoderm will eventually develop into the outer layer of skin and nervous system.
The head makes up nearly half of the size of the fetus. [8] Breathing-like movements of the fetus are necessary for the stimulation of lung development, rather than for obtaining oxygen. [9] The heart, hands, feet, brain, and other organs are present, but are only at the beginning of development and have minimal operation.
An ultrasound showing an embryo measured to have a crown-rump length of 1.67 cm and estimated to have a gestational age of 8 weeks and 1 day. Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump).