Pregnancy timeline: One to three days after conception

4 Aug

During the first days of pregnancy, cells divide to create duplicates of the original, fertilized egg. As genes become activated, the cells begin to communicate by sending and receiving chemical signals.

Compared to cells that will later allow baby to babble and barf, the first, original cell doesn’t have much to do. Before fertilization, the egg doesn’t need a lot of protein channels, or windows and doors through which it could “chat” with its neighbors. It has only to look for one thing in its environment: The wiggly-tailed sperm. It is set up with the chemical matrix to sense sperm, to help that first wiggler to traverse into its nucleus, and to create a barrier to deflect also-rans in the sperm race.

About a day after conception, the egg divides for the first time, making an exact copy of itself.

Only now that the egg is fertilized and is making its way down the fallopian tube will it develop the chemical recognizers it will need at the end of the week to lodge into the warm wall of the uterus. Creating them any sooner would be a waste of molecular time and energy, like putting wheels on a car that might never be driven.

Making their way womb-ward, the cells that began with the egg divide every 15 hours or so. Two days after fertilization, 2 cells become 4. On day 3, 4 cells become 8.

At about the 8-cell stage, the machinery within each cell starts to click into gear and turn on. The cells have not differentiated into distinct types like eye cells or liver cells; they are at this stage still “totipotent,” or capable of becoming any type of body cell.

But now, in addition to replicating their chromosomes in order to duplicate, they begin to activate genes to create little protein machines or structural scaffolding for the cells. And they begin to produce chemicals that are communicators and recognizers– transmitters and receivers of molecular messages.

Communication between little cells will drive the development of the embryo as a whole.

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One Response to “Pregnancy timeline: One to three days after conception”

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  1. The Science of Pregnancy Timeline– Week 0: Menstruation « - June 15, 2012

    […] Science of Pregnancy Timeline: Week 2  […]

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