Conception, fertilization, implantation: Our OBGYN explains the biology of early pregnancy and your baby.
You've been taking prenatal vitamins and tracking your cycles, and now you've decided you're ready to try to conceive. It's baby time! You've ovulated and had lots of sex, and now you are anxiously waiting two weeks till you can pee on a stick.
But what's actually going on during that endless-seeming two-week wait?
Around day 14 of the menstrual cycle, the ovary releases an egg that is captured by the fallopian tube. Picture the fallopian tube like a long tube with fingers at the end, which sweep around the ovary to grab the egg when it's released.
Once it's in the upper end of the fallopian tube, called the ampulla, the egg meets the sperm for fertilization, usually within 24 hours of being released.
Moving + growing
The fertilized egg then hangs out in the ampulla for about three days before making the three-day trip down the tube to the uterus. These first six days, however, aren't just about traveling from the ampulla to the uterus. While the egg is making this epic journey, it's also preparing for implantation by growing and dividing, growing and dividing. This allows the fertilized egg to become two cells, then four, and so on until becoming the 64-cell blastocyst, which is already starting to differentiate into what will become the placenta and what will become baby!
Over the next week, a complex series of events matures the blastocyst into an embryo while implanting it into the uterine lining.
It is also around this time that the outer layer of cells of the blastocyst start secreting human chorionic gonadotropin, or hCG. This is the hormone you've been waiting for, because hCG is what makes your home pregnancy test turn positive. hCG is detectable in the blood as early as eight days after conception, and the level keeps rising until it's high enough to be picked up in the urine by a home pregnancy test around the time of your missed period, 10 to 14 days after fertilization.
Even though that building anticipation during the 2WW can sometimes border on torture, keep this in mind: The pregnancy hasn't “stuck" until six to eight days after sperm meets egg, and it takes an extra week for the pregnancy hormone to rise to detectable levels. Hopefully, understanding these two weeks will help you take things one day at a time as your pregnancy begins.
References: Human Embryology & Developmental Biology, Fifth Edition. Bruce M. Carlson, MD, PhD. Copyright © 2014 by Saunders, an imprint of Elsevier Inc.