debated politically and academically. according to the conclusions of a review published in 2005, "evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester." however, developmental neurobiologists argue that the establishment of thalamocortical connections (at about 6+1⁄2 months) is an essential event with regard to fetal perception of pain. nevertheless, the perception of pain involves sensory, emotional and cognitive factors and it is "impossible to know" when pain is experienced, even if it is known when thalamocortical connections are established. some authors argue that fetal pain is possible from the second half of pregnancy. evidence suggests that the perception of pain in the fetus occurs well before late gestation whether a fetus has the ability to feel pain and suffering is part of the abortion debate. in the united states, for example, anti-abortion advocates have proposed legislation that would require providers of abortions to inform pregnant women that their fetuses may feel pain during the procedure and that would require each person to accept or decline anesthesia for the fetus. legal and social issues abortion of a human pregnancy is legal and/or tolerated in most countries, although with gestational time limits that normally prohibit late-term abortions. other animals fourteen phases of elephant development before birth a fetus is a stage in the prenatal development of viviparous organisms. this stage lies between embryogenesis and birth. many vertebrates have fetal stages, ranging from most mammals to many fish. in addition, some invertebrates bear live young, including some species of onychophora and many arthropods. the fetuses of most mammals are situated similarly to the human fetus within their mothers. however, the anatomy of the area surrounding a fetus is different in litter-bearing animals compared to humans: each fetus of a litter-bearing animal is surrounded by placental tissue and is lodged along one of two long uteri instead of the single uterus found in a human female. development at birth varies considerably among animals, and even among mammals. altricial species are relatively helpless at birth and require considerable parental care and protection. in contrast, precocial animals are born with open eyes, have hair or down, have large brains, and are immediately mobile and somewhat able to flee from, or defend themselves against, predators. primates are precocial at birth, with the exception of humans. the duration of gestation in placental mammals varies from 18 days in jumping mice to 23 months in elephants. generally speaking, fetuses of larger land mammals require longer gestation periods. fetal stage of a porpoise the benefits of a fetal stage means that young are more developed when they are born. therefore, they may need less parental care and may be better able to fend for themselves. however, carrying fetuses exerts costs on the mother, who must take on extra food to fuel the growth of her offspring, and whose mobility and comfort may be affected (especially toward the end of the fetal stage). in some instances, the presence of a fetal stage may allow organisms to time the birth of their offspring to a favorable season.