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How Big Is Baby?

From poppyseed to papaya, find out how big baby is at every stage during your pregnancy.

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Your Baby: Weeks 3 & 4

> In week 3, sperm meets egg, and voila: conception! Your little zygote sets off on a six-day trek through your fallopian tubes, dividing and redividing into identical cells as it travels to your uterus. Read more about baby this week.
> In week 4, now safe in your womb, the ball of cells (blastocyst) splits in two, becoming the embryo and the placenta. The amniotic sac and fluid are forming around baby, and will act as a cushion for the next eight months. Read more about baby this week.

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