by Ann-Marie Widstrom
A mother and her newborn infant can be regarded as a reciprocal biological unit where innate physiological mechanisms lead to instinctive behaviours that quicken emotional as well as physiological functions. From an evolutionary point of view this was a prerequisite for survival. The mother received impulses from her infant and understood how the infant should be nurtured, love ensued and she remained with the infant and provided protection and warmth, while the man provided other necessary conditions for survival.
In the animal world the first meeting between the mother and her offspring is controlled by a series of biologically programmed instincts and reflexes that are specific for each species. Soon after birth the newborn foal tries to stand up on its legs to reach its upright mother. Once standing on its wobbly legs, it begins to gently nudge under the mare’s belly with its muzzle, to try to find a teat to suckle.
Piglets usually find their way to the sow’s teats shortly after birth and begin to suckle. The piglet has such strong movements towards the teat that it breaks off the umbilical cord in the effort to reach the teat. In the first hours the piglets suckle independently of one another. Soon, however, the feedings are coordinated. When the sow gives special grunting signals the piglets begin to massage “their own” udder and the sow continues to grunt at an increasing frequency. When she has reached a frequency of one or two grunts per second, the piglets begin to suckle on “their own” teat. Before the milk begins to flow the piglets suckle with a low frequency. When the milk then lets down they begin suckling at a greater frequency. The sow lets down milk in her teats for only about 20-30 seconds. With this ingenious mechanism Nature ensures that the young are in place during the short period the milk flows and that the milk supply is guaranteed for all the piglets. When the piglets have finished suckling they once again begin to massage the udders. It is believed that with this “postmassage” they place an individual order for a specific amount of milk for the next meal.
It is not know exactly what leads a newborn infant to its mother’s breast but it can be assumed that the infant’s sense of touch plays a certain role. The senses of smell and sight are probably important as well. Experiments carried out on rats suggest that this is the case. If a rat’s teat is washed off directly after she gives birth, the prospects of the baby rat finding the teat and beginning to suckle are reduced. If the teat is then coated with the wash water, some baby rats regain the ability to find the teat. It is interesting to note that species born with open eyes are probably not as dependent on the sense of smell as is the rat, which has closed eyes for a period following birth.
In order for the mother to accept her young it is often of vital importance for the young to remain with the mother in the hours after birth. Imprinting, for example, occurs after a few hours with the ewe, to the smell of her own lamb. Another study shows that kids that are separated from their mother at birth are later rejected by the nanny goat when a reunion is attempted.
Some data suggest that maternal behaviour is controlled by hormones. If oxytocin is injected in a cerebral ventricle of a rat that has been treated with estrogen and progesterone, this causes maternal behaviour in the rat. The oxytocin levels are extremely high during childbirth. Oxytocin has thus been assumed to be a hormone that is important for the bonding of mother and infant. This assumption is supported by the fact that vaginal stimulation, which leads to increased oxytocin levels, extends the sensitive period after birthing during which an ewe will accept her lamb. A non-pregnant ewe that has been given estrogen and progesterone may after vaginal stimulation even adopt a strange lamb.
If a healthy newborn infant is placed on its mother’s chest with skin-to-skin contact directly after birth and then not disturbed, it exhibits predictable behaviour that leads to the infant without assistance finding its mother’s nipple and beginning to suckle at about one hour of age. After the cry at birth the infant at first usually lies still, relaxed and pale with no mouth- or rooting movements. After a while the infant begins to become active, it tries to open its eyes and after a bit longer closes its hand and bends its arm. At about 30 minutes of age it puts its hand to its mouth. This seems to stimulate an increase in mouth movements. The rooting reflex that was not present at first grows successively stronger and reaches a peak at the same time as the mouth movements, when the infant has crawled to the nipple in order to eventually begin to suckle.
At some time during this first period the infant usually tries to bend its head back and seek out its mother’s face and eyes. It could be that the mother’s voice causes the infant to look at her. The infant recognises its mother’s voice from the time in the womb and probably now associates the mother’s face with the already familiar voice. The first meeting with the mother is built on recognition — a “safe-and-sound” situation for the infant.
There are authors that do not believe there is a sensitive period in humans like the one in animals. But many studies suggest there is a sensitive bonding period in the hours after birth also in human beings. Among other things, it has been found that if mother and child have skin-to-skin contact immediately after delivery instead of being separated, the breastfeeding period will be lengthened and the mother will exhibit more devoted behaviour towards her infant.
Apart from skin-to-skin contact, the infant’s touch on the mother’s nipple in this period immediately after delivery seems to quickens the mother’s emotional bonding with her infant. A group of mothers whose infants had the opportunity to suckle at the breast within half an hour after birth spoke more with their infants and kept the infants for shorter periods of time in the nursery during their stay in the maternity ward than did a group of mothers whose infants first suckled at an average of eight hours postpartum. The group of mothers with early suckling contact also showed hormone levels that suggest that they felt calmer with their infants in connection with breastfeeding.
The results from these latter studies thus seem to support the assumption that there is an early bonding period even in humans. Just like baby animals, the infant has an innate biological program that leads to its finding its mother’s nipple and suckling precisely during the period when the mother is most sensitive to the infant’s touch/suckling on her nipple, so sensitive in fact, that she at an early stage exhibits a more devoted behaviour towards her infant. The theory that oxytocin may play an important role for mother-infant bonding is supported by the fact that the mother’s oxytocin levels seem to rise in the first hours after birth, and then gradually fall.
It must though be remembered that this early bonding period the first hours after birth, is not “the only” period during which the mother bonds to her infant. The sensitive period seems to be there. Why should we withdraw the opportunity from the mother and baby to early get close to each other. If, because of some medical reasons, is not possible for them to stay together the first hours after birth there are many other ways for the mother to bond to her infant. We found no long term effects of early touch of the nipple/suckling on variables such as length of the breastfeeding period and the mother’s emotional description of the infant.
Breastfeeding behaviour in the establishing phase
It is now known that the newborn has a large capacity for receiving impressions of the senses. Besides the infant “with undeveloped motor skills” being able to seek out the mother’s breast at an age of only one hour, the infant has, for example, the ability to focus its gaze and turn its head towards a sound. It is documented that the infant learns to recognise its mother’s voice when still in the womb. Two American research workers asked pregnant women to read the story “The Cat in the Hat” aloud for their unborn babies twice a day during the last six weeks of pregnancy. When the infants were a few hours old they had earphones put over their ears and a dummy (pacifier) placed in their mouth. By sucking on the dummy at different frequencies the infants could either hear their mother’s voice or another woman’s voice reading “The Cat in the Hat”. The infants preferred to suck at the frequency that led to their hearing the story with their mother’s voice. When an experiment was made so the infants could chose between hearing “The Cat in the Hat” and another story, both read by their mother’s voice, they chose by sucking frequency to listen to the story they had heard their mother read during the last stages of pregnancy, “The Cat in the Hat”. With the help of these exciting experiments one can assume that infants learn to recognise their mother’s voice when still a fetus and that they are also able to tell the difference between different stories, perhaps because the stories have different rhythms. Infants thus have a functioning memory even as a fetus. Probably the infants also recognise their father’s voice. If the father is asked to talk to the infant during the waking period in the first hour following birth, the infant will turn towards him and not be very interested in looking at a stranger who tries to get its attention. Other research has shown that the newborn can also imitate facial expressions. If the leader of the experiment sticks his or her tongue out the infant does so as well, if the leader yawns the infant may also do so. The newborn can thus differentiate between different facial expressions. Experiments conducted with two-day-old infants show that the infant can by sight tell its own mother from a strange woman of similar appearance. Experiments with infants who were six days old show that they can differentiate between the smell of their own mother and that of other lactating women.
There is a competence in the newborn that is important to trust in the breast-feeding situation. The infant shows clearly when it is hungry. It puts its hands to its mouth and tries to suck on them at the same time as it makes strong rooting movements from side to side with its head. If the infant is not successful with these signals it eventually begins to cry in order to get the attention of his mother. An infant that has been crying for a long time before breastfeeding has often more difficulty in settling down and beginning to suckle than an infant that has not been crying.
When the infant is a few days old and comes close to its mother’s breast it usually grows eager and sometimes perhaps impatient and begins to look for the mother’s breast with the reflex-like rooting movements. The infant brushes across the nipple and areola with an open mouth. It looks as if the infant “misses” its mark and does not find the nipple. But this “prelude” is important. Actually, what the infant is doing is to stimulate the nipple in order to latch on. When the nipple is pointed enough, this in turn stimulates the infant to a strong reflex with a maximum opening of the mouth simultaneously as it puts its tongue in the bottom of the mouth cavity in order to grasp the nipple with a movement of the head towards the breast. The infant then begins to suckle at a relatively low frequency until the mother lets down her milk, and the infant changes to rapid suckling when the milk lets down. Periods of rapid suckling are then alternated with periods of rest and eventually the suckling grows weak and the infant falls asleep. It can be tempting to shake the infant when it takes its breaks in order to get it to continue suckling. To disturb the infant during the breaks may cause it to become confused and lose its grasp of the nipple and it may even be delayed in its suckling.
Usually the infant has received most of the milk within five minutes but continues suckling a bit longer, “post-suckling”. At the beginning of a feeding the “thin” milk comes, which quenches thirst. Towards the end the rich milk comes, giving a feeling of being satisfied along with much nourishment. This explains why it is unwise to limit the time the infant suckles, and how important it is to let the infant finish at the first breast, before letting it suckle on the other breast.
There are similarities between the phases in the infant’s breastfeeding behaviour and the behaviour of piglets. The piglets’ suckling can be divided into
- “communication phase”
- “slow suckling”
- “rapid suckling”, and
The corresponding phases in the infant are
- “communication phase”
- “slow suckling”
- “rapid suckling”, and
Few pig farmers would consider trying to help healthy piglets take the teat or interrupt their suckling. Unfortunately there is a deeply-ingrained tradition among health workers to “help” healthy infants onto the breast. The workers grasp the back of the infant’s neck in one hand and the mother’s breast in the other. They then try with more or less force to get the nipple into the baby’s mouth. In all likelihood the natural reflexes of the infant can be disrupted by this. Some infants even seem to react with aversion to the breast after such treatment. The routines of the staff probably stem from the time when newborn babies were swaddled in thick blankets in order to keep warm when they were kept in the nursery, separated from their mothers. Then the infant did not have a chance to show its competence and it was necessary to help it find the breast.
Importance of hormone and nervous system for breastfeeding
The breasts have been prepared for milk secretion during the entire pregnancy, for instance by a successive increase in plasma levels of estrogen and prolactin. The milk-secreting cells in the alveoli in the mammary gland are richly surrounded by blood veins and synthesise among other things lactose, amino acids and fats. They also extract water and minerals and other substances such as antibodies from the maternal serum.
The tip of the nipple is highly innervated with sensory nerves. The outside of the nipple and the areola are not as innervated and are thus not as sensitive to touch as the tip of the nipple. When the infant suckles at the breast, sensory nerve receptors are stimulated in the nipple cells. These neural impulses are transmitted in the spinal cord and go via the vagal nucleus to the pituitary gland, whose anterior is stimulated into releasing prolactin and whose posterior is stimulated into releasing oxytocin. This causes the milk secretion and milk ejection respectively.
Oxytocin is secreted in the nerve cells that have their nucleus in the hypothalamus. The nerve cells stores oxytocin in its axon that goes down to and ends in the posterior pituitary which serves as a larder for oxytocin, that is released from there directly into the blood vessels. Other oxytocin fibres lead from the hypothalamus to the vagal nucleus and the oxytocin there stimulates the vagal nerve to release gastrointestinal hormones such as gastrin, cholecystokinin and insulin in and near the stomach. Gastrin stimulates the acid secretion and growth of the gastric mucosa. Cholecystokinin (CCK) stimulates the emptying of the gall bladder. Apart from this, CCK also has effects on behaviour in that it causes sleep and drowsiness after the ingestion of food. Insulin increases the ability of the cell to absorb nutrients. Both gastrin and CCK support the glucose-induced secretion of insulin. Gastrin and CCK thus work not only in regulating the gastrointestinal tract but also in controlling the metabolism of food.
Somatostatin is a hormone that has the opposite effect: it inhibits motility and secretion in the gut and also inhibits the release of gastrin, insulin and CCK. Indirectly, somatostatin is a growth-inhibitory hormone. Normally the level of somatostatin falls when food is ingested so that growth hormones are released.
Effects of suckling-stimulation in mother
Release of oxytocin
In connection with the infant beginning to suckle, the oxytocin levels in the blood increase almost instantaneously: sometimes they increase even before the infant begins suckling. When the oxytocin reaches the myoepithelial cells surrounding the alveoli, the milk ducts and the milk sinuses, these contract and the milk is ejected. Sometimes milk begins to drip from the nipple or is even forced out in a spray. This phenomenon is commonly known as the “letdown”. The reflex is often not felt during the first few days postpartum, but is later felt by the woman as a “tingling” or “twinge” in the breast and may even be somewhat painful. The letdown can also be conditioned so that it is elicited when the mother thinks about her infant or hears it cry.
When the infant suckles at the mother’s breast the level of somatostatin falls and the levels of gastrin and insulin rise. This hormone release causes the energy that the mother has stored during pregnancy in the form of fat deposits as well as the food she ingests during lactation to be used more efficiently for the energy demands of milk production. The gastrointestinal mucosa grows during lactation, probably as a result of the growth enhancing gut hormones being released when the infant suckles at the breast. Thus even the woman’s capacity for absorbing nutrients from the gastrointestinal tract increases during lactation.
It is well-documented that breastfeeding duration in smokers is shorter than in non-smokers. In women who smoke, the fall in levels of somatostatin is not as apparent when the infant suckles. Perhaps smokers do not get this hormone “injection” for milk production. This could be one reason why they do not breastfeed for as long as non-smokers.
Milk production is controlled by many factors. It is known that milk secretion starts after delivery regardless of whether or not the infant suckles at the mother’s breast. There is thus a biological programming that starts up the production. Suckling stimulation is however necessary in order to maintain milk production. At each breastfeeding the prolactin level rises and peaks approximately 20 minutes after the infant has begun suckling. It is also known that the number of times the infant suckles at the breast per day can affect milk production. Few suckling occasions per day (4-5 per 24 hours) in the first days of life statistically lead to little milk; frequent feedings (9-10/24 hours) are associated with a higher production. This could be due to the fact that the mother’s hormone system is optimally mobilised but perhaps due, as well, to the stimulation of the secretory cells in the breast.
We have seen that the mother’s bonding with her infant occurs earlier if the infant is allowed to nuzzle or suckle at her breast soon after birth. Each feeding can also be regarded as a bonding opportunity where there is a rise in the level of the “bonding hormone” oxytocin. Besides these effects it is documented that the mother often becomes sleepy and relaxed when breastfeeding.This effect can be regarded as Nature’s way of protecting the mother from outside disturbances during breastfeeding. Her attention is directed towards her infant.
It has been shown that newly-delivered women have changed personality traits. This is probably due to the hormonal changes during breastfeeding. The lactating woman is more appeasing and can handle monotony better than non-lactating women. This too seems to be Nature’s help to the mother and her infant. The mother is more sensitive to the infant’s signals. She is the one who best understands the desires of the infant and she does not grow “sick and tired” of the monotonous task of breastfeeding.
Effects of suckling-stimulation on infant
Studies of prematures show that the infants gain weight better if they suck on dummies (pacifiers) when being fed by gavage. There is also an increase in the gastro-intestinal motility. The gastric contents have been analysed on prematures being fed by gavage. The results show that the levels of the hormone somatostatin, which has a calming effect on the motility as well as inhibiting secretion of other intestinal hormones such as gastrin, cholecystokinin (CCK) and insulin, are appropriately lowered when the infant sucks on a dummy. Probably the sucking on a dummy stimulates the receptors in the infant’s mouth which leads to an increased vagal activity and release of functional gastrointestinal hormones. The infants thus get more efficient energy and grow better on the same amount of food if they are allowed to suck on a dummy during gavage feedings than if they are not allowed to suck on a dummy. Experience shows that it is good for prematures to suckle at the mother’s breast as early as possible. Feeding by gavage and providing a dummy is actually only a way of imitating Nature.
With this knowledge it is natural to imagine that the full term infant’s suckling at its mother’s breast soon after birth leads to the same type of hormonal secretion found in prematures. The first breastfeeding probably leads to an increase in the peristaltics in the infant and to the infant’s stomach being emptied in a natural way of amniotic fluid. It is not necessary to perform gastric suctioning, something which used to be done routinely in order to prevent the infant from vomiting and possible aspiration, of its stomach contents. The infant shows that it has a need to suckle and that it also wishes to suckle for quite a long period. The infant gets very fractious if suckling is interrupted. Perhaps infants that fall asleep after having suckled for as long as they desired fall asleep with a CCK-induced feeling of satisfaction.
Each time the infant then suckles it gets a suckle-stimulated release of gastrointestinal hormones in addition to the secretion that usually occurs when food reaches the stomach. This is an appropriate function in the newborn infant which in this way increases its ability of handling food during the phase in life when the growth rate is at a peak. Furthermore, breast milk contains hormones. Whether or not the infant uses these is not yet known.
De Casper, A.J., Fifer, W.P., (1980) “On human bonding: Newborns prefer their mothers’ voices”. Science, vol. 208, pp. 1174-1176.
Kevern, E.B., Levy, F., Poindron, P., Lindsay, D.R., (1983) “Vaginal stimulation: An important determination of bonding in sheep”. Science vol. 219, pp 81-83.
Klaus, M., Kenell, J., (1982) Parent-infant bonding. The C.V.Mosby Company, Toronto.
Uvnas-Moberg, K., Widstrom, A.-M., Marchini, G., Winberg, J., (1987) “Release of GI hormones in mothers and infants by sensory stimulation”, Acta Paedriat. Scand. vol. 76, pp. 851-860.
Uvnas-Moberg, K., (1989) “Gastrointestinal tract in growth and reproduction”, Scientific American, vol. 261, pp. 78-83.
Widstrom, A.-M., Ransjo-Arvidsson, A.-B., Christensson, K., Matthiesen, A.-S., Winberg, J., & Uvnas-Moberg, K., (1987) “Gastric suction in healthy newborn infants. Effects on circulation and developing feeding behaviour” Acta Pediatr. Scand., vol. 76, pp. 566-572.
Widstrom, A.-M., (1988) “Studies on breast-feeding: Behaviour and peptide hormone release in mothers and infants. Applications in delivery and maternity ward care” Diss., Karolinska Institute, Nursing research unit, Department of pediatrics.
Widstrom, A.-M., Wahlberg, V., Matthiesen, A.-S., Eneroth, P., Uvnas-Moberg, K., Werner, S., & Winberg, J., (1990) “Short-term effects of early suckling and touch of the nipple on maternal behaviour and breast-feeding performance” Early Human Development, Vol. 21, pp. 153-163.