Interactions between metabolic and reproductive functions in the resumption of postpartum fecundity

Lactation has long been recognized as a major determinant of interbirth intervals. The temporal pattern of nursing has been proposed as the mechanism behind lactational amenorrhea. We present a new model of the dynamic regulation of lactational amenorrhea that identifies maternal energy availability...

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Bibliographic Details
Published in:American journal of human biology 2009-07, Vol.21 (4), p.559-566
Main Authors: Valeggia, Claudia, Ellison, Peter T.
Format: Article
Language:English
Subjects:
Argentina
Breast Feeding
Energy Intake - physiology
Energy Metabolism - physiology
Female
Fertility - physiology
Humans
Indians, South American
Insulin - metabolism
Postpartum Period - physiology
Reproduction - physiology
Time Factors
Weight Gain
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Summary:Lactation has long been recognized as a major determinant of interbirth intervals. The temporal pattern of nursing has been proposed as the mechanism behind lactational amenorrhea. We present a new model of the dynamic regulation of lactational amenorrhea that identifies maternal energy availability as the main determinant of ovarian resumption. Variation in the intensity of lactation remains a component of the model as a determinant of the absolute energetic cost of milk production. However, maternal energy supply determines net energy availability; a larger energy supply leaves a greater net energy surplus than a smaller energy supply (lactation costs being equal). We characterize the hormonal postpartum profile of 70 lactating Toba women of Argentina. We use C‐peptide, which reflects maternal insulin production, as a measure of energy availability. Initially low, insulin production rises as the postpartum period progresses, reflecting the declining metabolic load of lactation. A short period of supernormal insulin production precedes menstrual resumption. The high levels of insulin may play a role in stimulating the resumption of ovarian activity, which in turn may help to resolve the transient period of insulin resistance. The dynamics of insulin sensitivity during lactation would aid in synchronizing the resumption of ovarian function with a reduction in the energy demands of milk production. This hypothesis is supported by the sustained weight gain experienced by lactating women during the months preceding the first postpartum menses. The link between fecundity and energy balance could serve as a mechanism for adjusting the duration of lactational amenorrhea to the relative metabolic load of lactation. Am. J. Hum. Biol., 2009. © 2009 Wiley‐Liss, Inc.
ISSN:1042-0533
1520-6300
DOI:10.1002/ajhb.20907