The embryonic time comprises 56 days, i.e., 8 weeks from the minute of fertilization. This time span is separated into 23 Carnegie stages and the stage classification is based exclusively on morphologic features. Carnegie stperiods are hence neither directly dependent on the chronological age nor on the size of the embryo. This deserve to be shown by two examples: The clocertain of the rostral neuropore occurs by definition in phase 11 and that of the caudal neuropore in stage 12. More, in between the 2fifth and 3second days of the pregnancy, the stages are determined according to the number of the somites 9-13 that have actually been stimulated. The individual steras therefore differ in just how lengthy they last .
|Fig. 1 - Incidence of deformities during pregnancy||Legend|
|Embryonic periodFetal period|
Fig. 1Segment A represents the embryonic duration in which the embryo is especially sensitive via respect to deformities. Within the first eight weeks, the incidence of deformities (blue curve), that result in miscarriperiods, decreases from even more than 10% to 1% during the fetal period (B). The frequency of neural tube defects decreases from 2.5% to 0.1% (green curve) by the end of the embryonic period. (2)
According to approximates, over 90% of the 4500 designated frameworks of the adult body are currently established - and have the right to be distinguished - during the embryonic period (1). Throughout the fetal period the organs that created throughout the embryonic period flourish and identify (organogenesis). Figure 2 reflects the miscellaneous temporal phases during a pregnancy. A rough classification is made by assigning trimesters (trimenon). The LMP (Last Menstruation Period) is not the actual beginning of the pregnancy yet serves as a point of referral for determining the date of ovulation and hence the moment of fertilization. Normally this occurs 14 days after the beginning of menstruation, however have the right to differ a lot temporally. From the time of the last duration, one estimates 40 weeks after the last menstruation in order to recognize the approximate date of birth (the second and third grid marks reexisting the lunar month
|Fig. 2 - Time calculations in the time of a pregnancy||Legend|
|Embryonic periodFetal period|
Fig. 2The schematic diagram shows the miscellaneous time durations throughout the entire pregnancy. LMP = Last Menstruation Period. The embryonic duration (A) lasts 8 weeks and also the fetal duration (B) from the nine week to the birth, i.e., 30 weeks.
In obstetrics the pregnancy weeks (PW) are normally reckoned from the date of the Last Menstrual Period (LMP). This is a allude in time that many women deserve to easily remember. Computed this way, the pregnancy lasts 40 weeks and also the embryonic duration - as necessary - 10 weeks. Caution is advisable, though, as soon as wishing to calculate the moment of ovulation - and therefore fertilization, carefully connected with it - because the moment of ovulation can vary and depends on many kind of factors (conditioned by the atmosphere and emotional aspects). In lutz-heilmann.info the tempdental indices (i.e., the PW), therefore, constantly describe the moment of fertilization also though in helpful midwifery the time complying with the LMP is still provided for computations. After the 8th week, the fetus takes on typical humale functions, also though at the finish of the initially trimenon, the head is still reasonably large in appearance. The eyes shift to the front and the ears and also nasal saddle are created. The eyelids are also clearly recognizable currently. On the body, fine lanugo hairs are developed, which at the moment of birth are reinserted by terminal hairs. The physiologic umbilical hernia that arises in the embryonic period 15-20 has largely disshowed up. In the second trimenon the mommy feels the initially motions of the child. In the last trimenon the subcutaneous fatty tworry is created and stretches the still wrinkled skin of the fetus. The skin becomes extended more and more through vernix caseosa. This is a whitish, greasy substance und consists of flaked off epithelial cells and sebaceous gland also secretions. In neonatology this vernix caseosa is an important criterion for judging the maturity of the child. If the birth occurs post-term, it disappears aobtain.
|Umbilcal cord via herniaNoseEyeEyelidEar (a: tragus, b: antitragus )MouthElbowFingerToesAtrophied embryonic tail bud||Telencephalon|
|© Professor Kohei Shiota, Kyoto University|
List of the chapters | Next off chapter