gestation period


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Gestation period

In mammals, the interval between fertilization and birth. It covers the total period of development of the offspring, which consists of a preimplantation phase (from fertilization to implantation in the mother's womb), an embryonic phase (from implantation to the formation of recognizable organs), and a fetal phase (from organ formation to birth).

There is widespread confusion over the duration of the gestation period in humans because of the way in which it is defined medically. The time of ovulation, and hence the time of fertilization, is difficult to determine in humans, so for purely practical reasons doctors measure the duration of pregnancy as the interval between the last menstrual period and birth, which is typically about 40 weeks or 280 days. For comparison with other mammals, however, the true gestation period between fertilization and birth in humans is about 267 days.

The length of the gestation period in mammals depends primarily on body size and the state of development of the offspring at birth. Large-bodied mothers have big offspring that take longer to develop, and development is also prolonged for offspring that are born at an advanced stage of development. Compared to all other mammals, human beings are found to have one of the longest gestation periods relative to body size.

One remarkable feature of mammalian gestation periods is that they show very little variability within a species. After excluding exceptional cases, departures from the average usually lie in a range of no more than ±4%. This is one of the smallest degrees of variability found in any biological dimension. See Reproductive system

gestation period

[jə′stā·shən ‚pir·ē·əd]
(embryology)
The period in mammals from fertilization to birth.
References in periodicals archive ?
Considering our results on embryonic measurements as approximate estimates obtained with a rough estimation technique it is suggested that the gestation period lasts approximately 9 to 11 months (Fig.
7 days to their gestation period after their first instance of threatened preterm labor vs.
Furthermore, the gestation period for pulmonary anthrax is anywhere from three all the way up to 60 days -- meaning not everyone exposed to a high concentration of virulent anthrax spores will suffer from a life-threatening infection at the same time.
If they make the three-month gestation period, the Scots will be the first in the world to clone pigs, which have proved much harder to produce than sheep.
After its elephantine gestation period the first Merced chip was delivered two weeks ago.
Unlike the long gestation period of the CD-ROM market, where everyone jockeyed to get rich on the other person's investment; DVD, and especially DVD-RAM, is receiving the coopetive assistance of drive, media, board, system, and content producers.
French's work, however, probably because of its long gestation period, reverses this relationship: The aftermath of trauma - in particular, his being badly wounded and, in general, his total experience in Viet Nam - rather than the politics of race becomes the book's central focus.
It's usually a two- to three-year gestation period as opposed to nine months.
For some technologies, the gestation period can be quite long, with development of a mass market always just around the corner.
The gestation period for Holsteins is about 280 days.
This translates into a restraint for the aerospace and defence (A&D) industry as it is capital intensive and investors are unwilling to commit sizeable amounts of money to an industry that has a longer gestation period compared to other industries.