Embriogenesis

My part of this shool work contains:
1- the duration of pregancy and its various developmental stages.
2- techniques of prenatal diagnosis
3- organogenesis
4- changes of baby positions throughtpregancy(visual context)





Duration
Healthcare professionals name three different dates as the start of pregnancy:
the first day of the woman's last normal menstrual period,
the date ofconception (about two weeks before her next expected menstrual period), and
the date of implantation (about one week after conception).
Since these are spread over a significant period of time, theduration of pregnancy necessarily depends on the date selected as the starting point chosen.
The most common system used among healthcare professionals is Naegele's rule, which was developed in theearly 19th century. This calculates the expected due date from the first day of the last normal menstrual period(LNMP) regardless of factors known to make this inaccurate, such as a shorter or longermenstrual cycle length. Pregnancy most commonly lasts for 40 weeks according to this LNMP-based method, assuming that the woman has a predictable menstrual cycle length of close to 28 days and conceiveson the 14th day of that cycle, and a birth between 37 and 42 weeks LNMP is considered full-term. Other, more accurate algorithms take into account a variety of other variables, such as whether this isthe first or subsequent child (i.e., pregnant woman is a primipara or a multipara, respectively), ethnicity, parental age, length of menstrual cycle, and menstrual regularity), but these are rarelyused by healthcare professionals.
There is a standard deviation of 8–9 days surrounding due dates calculated with even the most accurate methods. This means that fewer than 5 percent of births occurat exactly 40 weeks; 50 percent of births are within a week of this duration, and about 80 percent are within 2 weeks. It is much more useful and accurate, therefore, to consider a range of due...