Wikipedia and the scientific community
Birth & babies
These days it's not uncommon in the west for women to elect to have a water birth. In fact, most women who do choose to give birth in water, report that it is significantly easier, less painful or stress inducive and with fewer complications. For the fetus also, the transition tends to happen in a more relaxed manner, with newborn water babies often appearing more relaxed and scoring higher on the Apgar scale.
In the natural world, an animal will choose to give birth in the safest and easiest environment that is available to them. With the exception of fully aquatic animals such as whales, dolphins and sea-cows, and semi-aquatic animals such as hippos and sea-otters, no other mammal is known to voluntarily choose to give birth in water.
Amongst native peoples living in coastal regions it was traditional right up to recent times for women to go into the sea to give birth. This only ceased when the missionaries thought it wrong and made them stop. 
On average a baby spends nine months in water, receiving food and oxygen from the mother's body via the placenta and the umbilical cord. This continues to be the case during labour, so even when the baby's head is through the birth canal and in the water, there is no danger of the baby drowning. Additionally, the baby's lungs cannot expand to take a breath until it is completely born. And still there is no risk of the baby drowning. The baby will continue to receive oxygen from the mother until it makes contact with the air and attempts to take its first breath. Only when the baby is breathing independently, will the placenta begin to detach from the uterus and stop providing oxygen. Another reason why human babies will not attempt to draw a breath under water is because of what's called the diving reflex. As soon as the face makes contact with water, a metabolic shift occurs, forcing the heart rate to slow down and the throat to close off. This is strongest in new born babies.
One argument against the idea that women could have habitually given birth in water is that human babies lose heat very quickly. However in Russia it is quite common for women to give birth in the Black Sea at 19-20 °C.  Additionally, unlike terrestrial mammals, human babies are born with two kinds of fat: brown fat, which many young mammals have for quickly converting into heat and energy, and unusually, white fat, which aids buoyancy and provides good insulation in water.
There are a number of indications that during a part of our evolution, our ancestors habitually gave birth in water to babies that were meant to survive in water. Let's look at them one by one:
Human babies and fetuses are much fatter than their non-human counterparts. At around 30 weeks of gestation, with the bones and organs fully formed more energy goes into laying down quantities of fat - some of it around the organs as is standard in other mammals - but much of it as a layer under the skin, which is uncharacteristic. The accumulation of fat rapidly accumulates over the last 10 weeks of gestation, from 30 grams to 430 grams, so that at full term, fat accounts for 16 percent of overall body fat, as compared to about 3 percent in a new born baboon. There is only one other documented species of animal - a seal - that has comparable fat at birth . This rapid accumulation of fat continues after birth, as does brain growth, for several months before it begins to slow down. It's an enormous cost to the pregnant or lactating mother:
There is one obvious conclusion to be drawn from the fact that human fetuses are born with so much fat. It has a double purpose: it provides the best insulation in water, and it also makes the newborn buoyant.
During the third month of gestation, the human fetus begins to develop a fine coat of hair known as lanugo. By the twentieth week the head, face, body and limbs are all completely covered in hair. However, around the time the human fetus starts to accumulate its subcutaneous fat layer, it also begins to lose its lanugo, and by week 36, only a month or so before birth, this hair has almost always completely disappeared and the baby is born completely furless. As the process of development in the womb often reflects the genetic sequence of our evolutionary history, this would serve to demonstrate that we started losing our fur around the same time we started to develop an insulating fat layer. In other words, we lost a means of insulating ourselves on land and gained a far more efficient way of insulating ourselves in water.
Vernix Caseosa is the name of a white fatty/greasy coating on the skin of a human newborn baby. It consists of sebum excreted by sebaceous glands, mixed with dead skin cells and starts to develop around 17 weeks into the pregnancy. Some have tried to explain that vernix protects the baby’s skin while it is submerged in amniotic fluid but if this were true it would apply to other mammal babies too, which it doesn't. In fact the only other known mammal that gives birth to young covered in vernix is a seal. Harbour seals are born on land but enter the water 30 minutes or so after birth. They are covered in a layer of Vernix Caseosa that is somewhat thinner than that of human babies. Grey seals who enter several hours after birth are born with an even thinner coat and hooded seals that don’t enter the water for over a day have an almost undetectable coating, so there seems to be a correlation between the thickness of the vernix layer and the time at which the newborn will enter the water.
The fetus' brain
Brain size is not relative to body size and of all the great apes, Homo sapiens has the largest brain, and also has the hardest time giving birth, although this is not necessarily because of the size of the fetus' brain. At birth, the relative cranial capacity of a new-born human is 9.9 per cent of its body size, whereas a newborn chimpanzee is at 9.7%.  (In fact, the only large mammals in which relative brain size rivals our own are the dolphins and their relatives). Fossil evidence has shown that the hominid brain started expanding considerably in the last 2 million years or so and then started to slow down perhaps around 10,000 years ago, about the time we discovered agriculture.
Investing in a larger brain requires extra metabolic resources that would initially have to be supplied by the mother throughout pregnancy and lactation.This means that increased energy resources must have been consistently available to hominid mothers which enabled the fetus' brain to grow much faster. Professor Michael Crawford and others described a clear link between DHA/omega 3 (which can be found predominantly in aquatic foods) and brain growth. And yet, the hominid mother had to find a safe way to give birth to a large brained infant because, as a bipedal ape, her narrow pelvis and angled birth canal meant that there were inherent dangers in allowing the brain size of her infant to increase unrestrictedly. As opposed to the litters of rapidly breeding R-selected mammals (such as rodents) -- whose young are born blind, naked, underdeveloped and helpless -- the more highly evolved K-selected babies of slow-developing mammals are born in a very advanced state, often ready to run with their mothers after a few minutes. Human babies are the glaring exception to this rule. As Stephen Jay Gould said in 1977: "...we would spend 21 months in utero if our retardation in gestation matched the slow-down in our other systems." For this reason, it is believed that our ancestors were forced to make a pay off between giving birth to relatively helpless infant at an earlier stage of their development so that it could develop a larger brain. Between birth and the first four years of life, the human brain triples in size. 
The human newborn has different reflexes from other ape babies. An ape or monkey baby will be born with relatively strong muscles (stronger than in human babies) in its arms and fingers, enabling it to cling on to its mother's fur or grab hold of a branch. While a human newborn baby's palms will close tightly enough around an adult finger, the bones in its hands will not become fully ossified for many years and it cannot support its own weight. If you were to drop a newborn monkey, its first reflex would be to reach and grab, whereas a human newborn will spread its arms and legs wide apart, flexing and kicking. This would probably not help a newborn human dropped out of a tree, but it would and does help a human newborn, unsupported in water, to stay afloat.
From the moment of birth, the human infant demonstrates a diving reflex, which it will retain all its life if it continues to be exposed to a watery environment. That's why you can submerge young infants in water and they will immediately hold their breath, keep their eyes open, remain calm, and move their arms rhythmically in order to swim to the surface or the nearest person. (A child that does not learn this within the first 1-2 years of life will need to be retaught). Human babies are very at home in the water and amongst coastal people, such as the Moken, swimming is so natural it is common for children to learn to swim and dive under water before they can walk.
Another amazing reflex that human infants demonstrate is the ability to rotate in the water, from a face-down position, to floating on its back. This is one of the first things that is taught in baby swim classes and any child can learn it.
Other possibly relevant points...
|Website: F. Mansfield, 2015|
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