Scientific evidence about fertility while breast feeding is limited and yet the nursing mom needs to know if she can get pregnant - whether the goal is prevention or adding to the family.

In recent years scientific studies have confirmed that breastfeeding delays the return of fertility.

Women's postpartum fertility depends on many factors, some known and some yet to be discovered. These include lactation status and patterns that are dependent on the mother and her nursling while other variables such as the individual hormonal fertility thresholds; are still physiological mysteries.

The individual variations are huge. Statistically, half of all nursing women have a resumption of menses by the tenth postpartum month and a return of ovulation by the eleventh month.

About 19% of lactating mothers will become pregnant by the twelfth month if no contraceptive method is employed.

Many factors influence fertility while breast feeding. Research supports that in a most cases, the more frequently a baby is breastfed, the younger the baby is, and the less sustenance he gets from other sources - the later the mother's periods will return, the later she will be likely to conceive.

The contraceptive effects on fertility while breast feeding can function as a protective barrier against a new, unwanted pregnancy or alternatively present an barrier to bringing a desired new baby into the family.

Lactational Amenorrhea Method (LAM)

LAM naturally prevents fertility while breast feeding.

Mothers who use knowledge of lactation induced amenorrhea to regulate fertility benefit from the "Lactational Amenorrhea Method” or LAM.

Ovulation in the non-lactating woman may occur as early as three weeks after she gives birth. The chance of ovulation in the fully-breastfeeding, amenorrheic (meaning period has not returned) woman is less than 1-2%.

Frequent nursing stimulates prolactin levels, which suppress the surge of the follicle stimulating and luteinizing hormones and ovulation does not occur.

It has been shown in clinical trial that exclusive nursing is 98-99.5% effective in preventing fertility while breast feeding as long as all of the following conditions are met:

The infant is less than six months old.

The mother is amenorrheic (not menustrating).

The baby is breastfed around the clock without receiving other foods, supplements, or pacifiers.

These three facts are the foundation for Lactational Amenorrhea Method. The scientifically proven method utilizes lack of fertility while breast feeding.

A mother whose infant is less than six months old, has not had her periods return, and is fully or nearly fully breastfeeding is less than 2% likely to conceive.

Suppression of fertility while breast feeding is achieved through frequent nursing day and night.

Research has found that fertility will be reliably suppressed during amenorrhea as long as the majority of feedings are at the breast and the mother and baby go no longer than four hours during the day or six hours during the night between feedings.

Once the baby begins sleeping through the night there is an increased likelihood of fertility returning.

Lactation and Increased Conception of Twins

Twinning in general and identical twinning in particular are more likely to occur in mothers who are lactating at the time of conception.

Latest studies by Dr. Gary Steinman indicate a much higher rate of twin births to lactating mothers: 12.4% versus 1.1% in the non-lactating population. Dr. Steinman analyzed the effects of breastfeeding on twinning frequency in cases of pregnancies conceived during lactation. La Leche League participated in collecting data on mothers who experienced fertility while breast feeding and became pregnant.

Two key factors influencing identical twinning include ovulation induction and calcium channel blockers. In his research, Dr. Steinmann concluded that increased twinning is due to both temporary overshoot of FSH with recent resumption of menstruation and also to the significantly lower serum calcium levels in lactating women.

Ecological Breastfeeding

In Breastfeeding And Natural Child Spacing: How Ecological Breastfeeding Spaces Babies, Sheila Kippley describes ecological breastfeeding as the kind of nursing that most effectively spaces babies:

nursing on cue

keeping baby close

providing all nourishment and liquids at the breast for the first five to eight months

nursing to comfort the baby

It does NOT include the use of bottles or pacifiers, mother-baby separation, parent-imposed feeding schedules or restriction of night nursing. All of these practices limit the nipple stimulation that suppresses ovulation.

Many "ecological breastfeeding" mothers find they remain amenorrheic longer than six months.

The chances of pregnancy occurring during the first three months of ecological breastfeeding are very slight.

During the second three months, there is a less than 2% chance of becoming pregnant before the first menstrual period.

After six months postpartum there is a six percent chance of becoming pregnant before the first period.

During the second six months postpartum, an amenorrheic woman who is relying on ecological breastfeeding alone has a 94% chance of not becoming pregnant.

Women who practice ecological breastfeeding average 14.6 months of amenorrhea.

7% experience a return of their menses in the first six months following childbirth.

37% get their periods back during months seven to twelve.

48% get their periods back sometime during the second year after childbirth.

8% go longer than two years without periods. Despite the variability in the return of menses, there is not as much variation in the return of fertility as might appear.

Women who experience a return of their periods in the first six months tend to be infertile for a few cycles, while the early cycles of women experiencing a longer period of amenorrhea are often fertile.

Weaning and Fertility

In some cases, even infrequent breastfeeding is enough to prevent pregnancy. The nursing mother who wishes to regain her fertility while breast feeding sometimes faces tough decisions about her existing breastfeeding relationship.

For many women a threshold of 100 minutes of breastfeeding per day keeps them from regaining fertility while breast feeding.

Weaning an older nursing child in order to conceive may also present challenges. Doctors are not always supportive of breastfeeding a toddler in general, much less when the mother is trying to conceive or is already pregnant.

If the mother was experiencing lactational amenorrhea, the reduction in nursing frequency will stimulate the return of fertility even while breast feeding relationship continues. The hormonal state of the mother will also change with the cessation of breastfeeding as prolactin returns to pre-reproductive levels.

Conclusion

Suckling is the crucial interaction between the baby and the mother that causes loss of fertility while breast feeding.

Although the exact mechanism by which breastfeeding causes this are not yet known, it's clear that suckling activity is the major controller of the duration of lost fertility while breast feeding.

Scientific advancement has driven us in the pursuit of an equation, or formula involving the breastfeeding stimulus that would solve the mystery of the mechanism of lactational infertility. Researchers continue to study and learn about the vast diversity in breastfeeding behavior, and the larger numbers of participants and varied locations around the world add to the comparative multiplicity in human physiology that has now been seen.

There is some diversity in every aspect of human anatomy and physiology; amongst people of the same faith and background and between races and ethnicity, and it would be inaccurate to think that defining the relationship between breastfeeding and fertility is a straightforward measurement question.

To date there is no evidence to adequately explain the range of responses to breastfeeding stimulus.

We can only hope that researchers will continue to study important facets of breastfeeding behavior that may help improve our ability to measure the effects of breastfeeding on fertility.

Science has come a long way in better understanding the relationship between supplementation and the return of fertility.

Early studies seemed to say that supplemental feeding was so closely related to ovulation that it might actually cause it. Later studies oppose that theory by showing that supplemental feeding does not always reduce breastfeeding frequency - as seen when infants are slowly introduced to small portions of solid foods. Suitably, supplementation does not always lead directly or quickly to ovulation.

While we are still unable to measure or predict the exact duration of lactational amenorrhea perhaps the most encouraging results of current research will be positive changes in breastfeeding practices caused by the wish to employ scientific and natural methods of contraception while ultimately providing superior infant nutrition.

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References to Fertility While Breast feeding article