What are the stages of human development before birth?

The stages go from fertilisation (when the egg is fertilised), to an embryo, then the sex of the baby is decided. Occasionally two eggs are fertilised, which creates twins. Rarely, one embryo splits into two and both cells develop separately, as identical twins, similar in appearance. The journey along the Fallopian tube continues slowly for about four days. Growth increases. The uterus is forming a spongy lining within which the embryo will implant. To achieve this the embryo burrows into the wall of the womb and is covered over by the lining of the womb. This begins 6 days after fertilisation and is completed within the next 7 days. This is all in the first month. The baby keeps on developing until conception, which is usually in or after the 9th month. Its hands, eyes and ears start developing properly and it becomes sensitive to sound and responsive to touch. Around 8 weeks, the embryo becomes a foetus and at 9 weeks, it can bend its hand around an object. At 12 weeks he can close his fingers and thumb and he will open his mouth in response to pressure applied at the base of his thumb. The senses continue to develop until the 9th month, when the baby is born.

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