gestation period

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.

gestation period

gestation

[jes-ta´shun] the period of development of the young in viviparous animals, from the time of fertilization of the oocyte (ovum) to birth; see also pregnancy.gestation period the duration of pregnancy" >pregnancy; in the human female, the average length, calculated from the first day of the last normal menstrual period, is 280 days, or 6 lunar months. The normal limits of the human gestation period are from 37 weeks (259 days) to 42 weeks (293 days); days and weeks are counted as completed days and weeks. If one counts from the moment of conception, the length of time is 266 days (280−14 days).

period

[pēr´e-od] an interval or division of time; the time for the regular recurrence of a phenomenon.absolute refractory period the part of the period" >refractory period from phase 0 to approximately −60 mV during phase 3; during this time it is impossible for the myocardium to respond with a propagated action potential, even with a strong stimulus. Called also effective refractory period.blanking period a period of time during and after a pacemaker stimulus when the unstimulated chamber is insensitive to avoid sensing the electronic event in the stimulated chamber.effective refractory period absolute refractory period.ejection period the second phase of systole" >ventricular systole (0.21 to 0.30 sec), between the opening and closing of the semilunar valves, while the blood is discharged into the aorta and pulmonary artery. Called also sphygmic period.gestation period see gestation period.incubation period see incubation period.isoelectric period the moment in muscular contraction when no deflection of the galvanometer is produced.latency period 1. latent period.2. stage" >latency stage.latent period a seemingly inactive period, as that between exposure to an infection and the onset of illness (incubation period) or that between the instant of stimulation and the beginning of response (latency, def. 2).refractory period the period of depolarization and repolarization of the cell membrane after excitation; during the first portion (period" >absolute refractory period), the nerve or muscle fiber cannot respond to a second stimulus, whereas during the period" >relative refractory period it can respond only to a strong stimulus.relative refractory period the part of the period" >refractory period from approximately −60 mV during phase 3 to the end of phase 3; during this time a depressed response to a strong stimulus is possible.safe period the period during the menstrual cycle when conception is considered least likely to occur; it comprises approximately the ten days after menstruation begins and the ten days preceding menstruation. See the section on fertility awareness methods, under contraception.sphygmic period ejection period.supernormal period in electrocardiography, a period at the end of phase 3 of the action potential during which activation can be initiated with a milder stimulus than is required at maximal repolarization, because at this time the cell is excitable and closer to threshold than at maximal potential" >diastolic potential.vulnerable period that time at the peak of the T wave during which serious arrhythmias are likely to result if a stimulus occurs.Wenckebach's period a usually repetitive sequence seen in partial heart block, marked by progressive lengthening of the interval" >P–R interval; see also beat" >dropped beat.

gestation period

The period from fertilization of the egg (ovum) to the birth of the child. The human gestation period is 40 weeks, plus or minus 2 weeks.

gestation period

gestation period

gestation period

Gestation period

gestation period

gestation period

gestation

period

gestation period

gestation period

Synonyms for gestation period

noun the period during which an embryo develops (about 266 days in humans)

Synonyms

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