Tag Archives: Week 0

The Science of Pregnancy Timeline– Week 0: Menstruation

15 Jun

Note: Because it can be hard to pinpoint exactly when a sperm and egg have merged, it is customary for midwives and doctors to start pregnancy calendars using the date of the mother’s last menstrual period, placing fertilization at “pregnancy week 2.”  To make this timeline consistent with the ones used for health visits (and other great timelines you may be reading), we are starting this one at “Week 0: Menstruation.”

The lining of the uterus– replaced monthly– is made to create a plush home for a fertilized egg.

The inner lining of the uterus is a big, red, comfy couch.

Its plushness is in place to welcome a fertilized egg to the dark, gentle world it will inhabit during nine months of growth. When no guest arrives, the luxurious couch goes out to make room for the next.

Menstruation is the end of one cycle and the beginning of the next. A signal goes out to the ovaries to begin preparing a new egg for release, two weeks later, into the fertile zone of the fallopian tubes.

An egg on this journey has already been through epic travels; it originally developed within your ovaries when you were just a fetus inside your mother’s uterus!

Each egg itself is a universe. What other thing in the entire world is so small and gives rise to something as large, beautiful, complex and long-lived as a human being? The egg’s capacity for creation precedes us by millennia and continues on in every species on the planet, in the annual bloomings of spring and the monthly cycles of women everywhere.

At the time of ovulation (two weeks before menstruation), the egg is at the edge of the island of the ovary. Hormones, a little like weather patterns, churn the seas around the ovaries until the egg breaks loose. This package is transferred directly to the superhighway of the fallopian tubes, where a journey of 3 to 4 inches will take several days. This is when fertilization may take place.

Typically, this journey toward the uterus is pretty solitary for the egg. It might hit viruses or bacteria, depending on the mother’s health. It could hit a road block if the mother’s had her tubes tied. And it could end up in a town of Hell’s Angels, and that’s the guy you just slept with.

If  fertilization happens, the egg will plant itself in the wall of the uterus. This big couch is also like the deep, rich, dark soil that you would find on the forest floor, where almost anything can grow.

If the egg is not fertilized within a day or two, it simply dissolves back into all that luscious warmth. Menstruation happens. And the cycle begins anew.

What’s next

Science of Pregnancy Timeline: Week 2 

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The Big. Ass. Egg.

About this timeline: Genedoe is an educational blog that aims to enhance the public's understanding of genetics– a topic that can inspire us to be healthier, to fathom the diversity and connectedness of living things on the planet, and to explore the comedies and tragedies that befall the human body.  The "Science of Pregnancy Timeline" is a 40-week calendar that we hope parents will read in conjunction with their nine months of expecting. (We will occasionally address 'you' with the assumption that you are a pregnant woman; we beg your pardon if this does not apply, and welcome you to our blog, where genetics is for everyone.) Thank you for your comments and your partnership in plumbing the depths and the wonders of pregnancy!