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Video transcript

gestation is a term that most people use synonymously with pregnancy now many people use the term conception to define when a pregnancy or gestation starts now conception is kind of a cloudy term and there's not really a good definition for what it means so in general it's probably best if we just don't use that term all together now everybody is a little bit more clear on when gestation ends and that is of course birth so we'd like to break this process down a little bit further is there an easy way that we can do that well we've all been told that gestation or pregnancy lasts about nine months so we can draw another timeline here here we've got to divide it out into month-long segments and you can see I've got 1 2 3 4 5 etc and you've also probably heard the term trimester and the trimester is a useful concept too now pregnancy lasts about nine months and you can divide that into three equal sections so here we have a division into the first trimester in the second trimester and the third trimester you can see this potentially goes out beyond nine months first second and third but we can debate it up more than that in fact it's most useful to define it in terms of weeks so here on the same scale I've just given us week segments instead of monthly segments I'll put marks at 10 20 30 40 weeks so you can see basically how these are laid out we have the same time frame here the pink arrow measures the entirety of pregnancy the blue timeline is four months the red timeline is trimesters and the green timeline is four weeks so going back to the fact that conception is not that great a term we know that it happens somewhere here around the beginning of pregnancy but to be a little bit more precise it's probably best to define these time points so if we're calling this week zero we have to be able to count from something and the thing that most people use to count from is the last menstrual period this is usually something that's relatively easy to pick out and in medical terms that's usually abbreviated to LMP now of course that's not when fertilization happens fertilization actually happens here at week two and you'll remember that fertilization is when an egg is met by a sperm and genetic material is combined after fertilization occurs we can start embryo Genesis now embryo Genesis lasts about ten weeks and by the end of that period we've started at a single cell and we've divided and divided and differentiated those cells and we've gotten to the point where all of our organ systems are formed so we've undergone organ Genisys from this point on we're considered a fetus and we continue to develop but we call it fetal development along the way we pass some very important milestones here at roughly 24 weeks we hit a milestone of 50% survival and that 50% survival is outside the womb so if you're born at about 24 weeks you have even odds of actually surviving but after 24 weeks your complication rate significantly declines and here we get to the end of our 39th week at that point we are full-term there's a little bit of leeway in this definition and most people consider full-term to be arranged around 40 weeks extending from 37 weeks to 42 weeks before that and we're in preterm territory after that and we're in post-term territory most people know that there can be complications to being born preterm but there are actually also complications to being born post-term for instance you might be too big to fit through the birth canal the best outcomes happen in this range of being born term so there you have it while pregnancy and gestation is one long continuum it can be divided into sub parts like months trimesters or to be probably the most scientifically accurate and useful weeks you start counting at the last menstrual period at week zero fertilization happens at week two you go through embryo Genesis organogenesis fetal development along with a period of growth and further development before birth at the end of pregnancy