Oxytocin: Key Hormone In Sexual Intercourse, Parturition, And Lactation


As early as 1967 the anthropologist Margaret Mead, joined by psychologist Niles Newton, published some important observations on the laboring patterns of two separate cultures in Central and South America. In one culture, the Cuna Indians of Central America, coitus and birth were viewed with shame, and labor and delivery were orchestrated by a medicine man who, though not present at the event, made medicinal teas which he gave to the midwives to administer. Labors were reported to be prolonged and agonizing. In contrast, these authors observed the Siriono Indians in South America, who labored in their hammocks in communal huts. Family and friends attended a woman in labor and, on average, her labor and delivery lasted one to three hours.

Niles Newton went on to pioneer research on the labor process and focused attention on the hormone oxytocin. In 1971, she published a series of articles on the interrelationship between coitus, childbirth, and lactation. She proposed that these reproductive events share at least three characteristics:

- they are based on closely related neurohormonal reflexes;

- they are sensitive to environmental stimuli, being easily inhibited in their early stages;

- they all, in certain circumstances, trigger caretaking.

Newton and her husband, Dr. Michael Newton, an obstetrician, had been looking at the psychological aspects of human lactation since the 1940s. They had confirmed, with a human subject, earlier findings that cows will not "let down" their milk easily when a cat is put on their back or when given an injection of adrenalin.( 1, 2, 3, 4) As Newton develops her thesis, she suggests that this inhibition of milk let down (or the milk ejection reflex) was built into mammalian psychophysiology as a safeguard from milk stealing. She goes on to point out that the key role of oxytocin in human sexual excitement and climax, in the normal progress of labor and delivery, and in the milk ejection reflex during breastfeeding, can be inhibited by adrenaline or the fight or flight reaction if danger approaches. In all three instances, mammals, including humans, would be vulnerable to attack or danger, and thus could be protected by a negative feedback system which would 1) block the trance-like sta te that occurs during sleep and sexual arousal, 2) stop the progress of labor until safer surroundings are found, or 3) inhibit milk let-down until mother and baby can safely feed.

Newton's and others' work nearly 50 years ago lays the basis for the argument that successful initiation of lactation is most likely if the entire reproductive process is preserved in a setting of social support free of fear and danger. Oxytocin's role in this process is now undisputed, yet unfortunately it is ignored by many practitioners of modern obstetrics. Let us turn now to some individual labor and delivery practices as they have evolved with the move toward parturition in the hospital, and examine how these practices might directly or indirectly impact upon lactation.

Laboring Alone vs. Laboring With Support

While it seems unnecessary to have to compile a body of research literature to prove that a woman labors more quickly and effectively with a supportive person at her side, such literature is now accumulating and being published in widely read medical journals. With the advent of the natural childbirth movement in Europe in the 1950s and 1960s, both Dr. Fernand Lamaze in France( 5) and Dr Grantly Dick-Read in England( 6) wrote of the importance of "help" and "attention" to the laboring woman.

In the 1970's a leading proponent of family-centered home birthing in the United States, Ina May Gaskin, advocated in Spiritual Midwifery the importance of a laboring mother "cuddling" and "smooching" with her partner.( 7) In light of the earlier discussion about the importance of oxytocin in both sexual intercourse and in laboring and birth, this advice from Ms. Gaskin, a practicing midwife, is well founded.

Over the last twelve years some important studies have looked at the importance of a supportive labor companion (often termed a "doula") during labor and subsequent birth outcome. Sosa et al. in Guatemala( 8) looked at 20 low-risk primigravida women in labor who were supported by a lay "doula" and 20 controls. Women were removed from the study if they had prolonged labor, fetal distress, need for oxytocin augmentation, or cesarean section. As an incidental result, the authors were surprised to find that far fewer of their doula supported group had to be excluded from the study due to any of the aforementioned complications. Overall, their findings were that the supported group of mothers had significantly shorter labors: 8.8 hours on average vs. 19.3 hours in the control group. The supported mothers were more awake after delivery, and stroked, smiled at, and talked to their babies significantly more as well.

Following this work, the same authors looked directly at maternal and infant morbidity in a much larger randomized control study at the same Guatemalan hospital.( 9) They found that the supported group (N = 168 after exclusions) benefited in the following ways: fewer C-sections, less need for oxytocin augmentation, shorter labors, and fewer perinatal complications overall.

Kennell et al. again brought essentially the same research question to a large American hospital.( 10) In a randomized controlled study, two experimental groups and one control of approximately 200 each were sought. Healthy primigravidas only were included in the study. One experimental group was assigned a trained doula and the other group was simply assigned an observer who was present in the room but neither touched nor spoke to the laboring woman.

Their results were dramatic and have been clearly summarized by Penny Simpkin in a paper reviewing the literature on labor support:( 11) see Table 1.

Another important study on companionship in labor was published in 1991 by a group of South African investigators.( 12) They looked at the impact of a doula on labor, on the length of labor, labor pain perception, and use of analgesia. In addition, they looked beyond immediate perinatal outcomes and questioned mothers on their anxiety scores and their self-esteem measurement the day after delivery. The current anxiety score was lower and the overall sense that they had coped well with labor was higher in the supported group. A final important set of measurements were made at six weeks postpartum and focused on feeding practices. The group of women who had been supported in labor were exclusively breastfeeding at a significantly higher rate (51.4%) compared to the control group (29.3%). The supported group was feeding with more flexible schedules, had fewer feeding problems, found mothering easier, and felt their babies had no problems with their appetite. These results are summar ized below: see Table 2.

Midwives have known the importance of labor support for millennia, and the literal translation from the Old English of the word "midwife" is "with woman." The studies discussed here show convincing evidence that the effects of supportive companionship in labor go beyond reducing a laboring woman's fear or strengthening her pain tolerance. There are significant improvements in perinatal outcomes including lowered cesarean and forceps delivery rates, fewer oxytocin augmentations, less use of analgesia and anesthesia, shorter labors, and shorter infant hospitalizations. The recent South African study links labor support, and all the ensuing improved perinatal outcomes, directly to breastfeeding success at six weeks postpartum. This is an important study and suggests that obstetrical intervention during labor needs closer scrutiny so far as the impact on infant neurological development, including breastfeeding behaviors, is concerned.

This article is an excerpt from a longer presentation, "Labor and Delivery Practices: The Eleventh Step to Successful Breastfeeding" which was given at the 23rd Triennial International Congress of Midwives in Vancouver, Canada in May 1993. Mary Kroeger, CNM, MPH has practiced and taught midwifery for the last 17 years and nearly half of this practice has been outside the United States. Mary has lived and worked long term in Belize, Swaziland, Somalia, Kazakhstan and Central Java. She has also done short term consulting work in Nigeria, Uganda, Zambia, Uzbekistan, Turkmenistan, and Kyrgystan, as well as in other provinces of Indonesia. A lactation specialist, Mary has focused her international training activities on the importance or "mother and baby friendly" principles in all aspects of reproductive care.

Effects of Emotional Support During Labor Table 1 Outcome

Supported Observed Control p Value Narcotic analgesia

* 21.7%
* 28%
* 25.5% no difference Epidural anesthesia
* 7.8%
* 22.6%
* 55.3% <.0001 Oxytocin augmentation 17%
* 23%
* 43.6% <.0001 Duration of labor (mean)

* 7.4 hours 8.4 hours 9.4 hours =.0001 Cesarean delivery
* 8%
* 13%
* 18%

=.009 Forceps delivery

* 8.2%
* 21.3%
* 26.3% <.0001 Prolonged hospitalization of newborn

* 10.4%
* 17%
* 24%

<.001 Sepsis evaluation

* 4.2%
* 9.5%
* 14.7% <.001 Maternal fever
* 1.4%
* 7%
* 10.3% =.0007

Questionnaire Responses at Six Weeks Postpartum Table 2

Support Group Control Group



P < Breastfeeding only

* 38 (51.4%)
* 22 (29.3%)
* 0.01 Flexible feeding interval 60 (81.1%)
* 35 (46.7%)
* 0.0001 Has feeding problems
* 12 (16.2%)
* 47 (62.7%)
* 0.0001 Found mothering easy
* 33 (44.6%)
* 8 (10.7%)
* 0.001 Baby has poor appetite
* 0 (-)
* 19 25.3%
* 0.001


(1) Newton M and Newton N (1948) The let-down reflex in human lactation. J. Pediatr 33:693-704.

(2) Newton M and Newton N (1950) Relation of the let-down reflex to the ability to breastfeed. Pediatrics 5:726-733.

(3) Ely F and Petersen WE (1941) Factors involved in the ejection of milk. J Dairy Science 24:211.

(4) Petersen WE and Ludwick TM (1942) The hormonal nature of factors causing let-down of milk. Federation Proceedings 1:66.

(5) Lamaze F (1954) Painless Childbirth: The Lamaze Method Chicago: Contemporary Books, Inc.

(6) Dick-Read G (1979) Childbirth Without Fear 4th ed. New York: Harper and Row.

(7) Gaskin IM (1990) Spiritual Midwifery, 3rd ed Summertown, TN: The Book Publishing Co.

(8) Sosa R. Kennell J. Klaus M. et al (1980) The effect of a support companion on perinatal problems, length of labor, and mother infant interaction. N Engl J Med 303 (11):597-600.

(9) Klaus M. Kennell J. Robertson SS. Sosa R. (1986) Effects of social support during parturition on maternal and infant morbidity. Br Med J: 293 (6547):585-587.

(10) Kennell J. Klaus M. et al (1991) Continuous emotional support during labor in a U.S. hospital. JAMA 265(17):2197-2201.

(11) Simpkin P (1992) The labor support person: latest addition to the maternity care team. ICEA Review 16 (1): 19-27.

(12) Hofmeyr GJ et al (1991) Companionship to modify the clinical birth environment: effects on progress and perceptions of labor and breastfeeding. British J of Obstetrics and Gynaecology 98: 756-764.

Ina May Gaskin.


By Mary Kroeger

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