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The limit of viability is the gestational age at which a prematurely born fetus/infant has a 50% chance of long-term survival outside its mother's womb. With the support of neonatal intensive care units, the limit of viability in the developed world has declined since the 1960s. [33] [34]
When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the fetus through the birth canal, which is the vagina. The ova, which are the female sex cells, are much larger than the sperm and are normally formed within the ovaries of the fetus before its birth.
Pregnancy is the time during which one or more offspring develops inside a woman's uterus (womb). [4] [13] A multiple pregnancy involves more than one offspring, such as with twins. [14] Pregnancy usually occurs by sexual intercourse, but can also occur through assisted reproductive technology procedures. [6]
Fertilization was not understood in antiquity. Hippocrates believed that the embryo was the product of male semen and a female factor. But Aristotle held that only male semen gave rise to an embryo, while the female only provided a place for the embryo to develop, [5] a concept he acquired from the preformationist Pythagoras.
If given expert postnatal care, some preterm babies weighing less than 500 g (1 lb 2 oz) may survive, and are referred to as extremely low birth weight or immature infants. [ 21 ] Preterm birth is the most common cause of infant mortality, causing almost 30 percent of neonatal deaths. [ 22 ]
The sacred text is full of symbolism and timeless truths about pregnancy.
This is an accepted version of this page This is the latest accepted revision, reviewed on 6 January 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 Y ...
Fetal hemoglobin, or foetal haemoglobin (also hemoglobin F, HbF, or α 2 γ 2) is the main oxygen carrier protein in the human fetus.Hemoglobin F is found in fetal red blood cells, and is involved in transporting oxygen from the mother's bloodstream to organs and tissues in the fetus.