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This is an accepted version of this page This is the latest accepted revision, reviewed on 10 February 2025. Procreative biological processes of humanity Part of a series on Sex Biological terms Sexual dimorphism Sexual differentiation Feminization Virilization Sex-determination system XY XO ZW ZO Temperature-dependent Haplodiploidy Heterogametic sex Homogametic sex Sex chromosome X chromosome ...
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.
Gestational age: 2 weeks and 0 days until 2 weeks and 6 days old. 15–21 days from last menstruation. Embryonic age: Week nr 1. 0 (whole) weeks old. 1–7 days from fertilization.
GCSE Bitesize was launched in January 1998, covering seven subjects. For each subject, a one- or two-hour long TV programme would be broadcast overnight in the BBC Learning Zone block, and supporting material was available in books and on the BBC website. At the time, only around 9% of UK households had access to the internet at home.
Preterm birth is the birth of an infant at fewer than 37 weeks gestational age. Globally, about 15 million infants were born before 37 weeks of gestation. [152] Premature birth is the leading cause of death in children under five years of age though many that survive experience disabilities including learning defects and visual and hearing ...
According to the WHO, a preterm birth is defined as "babies born alive before 37 weeks of pregnancy are completed." [20] According to this classification, there are three sub-categories of preterm birth, based on gestational age: extremely preterm (fewer than 28 weeks), very preterm (28 to 32 weeks), moderate to late preterm (32 to 37 weeks). [20]
Implantation is the first stage of gestation, and, when successful, the female is considered to be pregnant. [3] An implanted embryo is detected by the presence of increased levels of human chorionic gonadotropin (hCG) in a pregnancy test. [3] The implanted embryo will receive oxygen and nutrients in order to grow.
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). [1] It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth. [2]