Page 5 - SONO 260 THE FIRST TRIMESTER
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The inner part of the blastocyst will develop into the embryo, amnion, umbilical cord, and the primary and secondary yolk sacs.
The outer part, the trophoblastic tissue, will develop into the placenta and chorion.
¡ On days 20 or 21 of the menstrual cycle, the blastocyst begins to implant into the decidualized endometrium at the level of the uterine fundus.
¡ By 28 days, complete implantation has occurred and all early connections have been established between the gestation and the mother.
¡ The blastocyst makes these links with the maternal endometrium via small projections of tissue called chorionic villi.
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