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Friday 20 April 2018

Mechanisms of Twinning IX: Influence of Prior Lactation

                                              http://austinpublishinggroup.com/nutritional-disorders/



The purpose of this study is to ascertain a physiological relationship between prior lactation and the probability of subsequent multiple pregnancies in humans, thereby lending support to the role of insulin-like growth factor in both phenomena. Data were collected in the present study to determine if there is a direct relationship between the extent of lactation in prior pregnancies and the chance of twin/triplet gestations subsequently. Positive results of such a study could support the proposed biochemical significance of insulin-like growth factor elevation in promoting multi-fetal pregnancies.
Cows with an enhanced tendency to twin have elevated levels of serum Insulin-like Growth Factor (IGF). IGF is a protein component of milk; bovine milk has a lower level of IGF than human milk, in general. Recent reports support the view that twinning in humans is also related in some way with IGF. Somatotropin-stimulated IGF augmentation often induces ovarian hyperstimulation in subfertile women undergoing in vitro fertilization. On the other hand, one small study found no significant difference in plasma follicle stimulating hormone (FSH) between mothers of Dizygotic (DZ) twins and mothers of singletons at any stage of the menstrual cycle.

Insulin-like growth factor, a 70-unit polypeptide, is a major mediator of FSH action on the ovary. IGF increases the sensitivity and responsiveness of ovaries to FSH. Variations in either FSH or IGF can modify the Spontaneous Twinning Rate (STR). The mitogenicly powerful synergistic combination of IGF and FSH enhances ovarian steroidogenesis, increases primordial follicle recruitment, and reduces ovum apoptosis, thus increasing the chance for double ovulation.  In humans, conceptions that occur while the mother is breast-feeding result in twin gestation rates (both monozygotic and dizygotic) nine times higher than in the general gravid population. Also, women who have ever lactated have a higher mean plasma IGF level than those who never lactated.

Human grand-multiparas (parity>4) more often breast-feed than women with fewer pregnancies. Also, elderly (age>40) grand-multiparas retain their fertility longer and conceive twins more often than do women of low parity. Thus, the current potential for twinning may be a function of lactation in prior pregnancies. By its cumulative effect, prolonged lactation might extend the period of enhanced availability of IGF.

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