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  • Title: Mechanisms of twinning. IV. Sex preference and lactation.
    Author: Steinman G.
    Journal: J Reprod Med; 2001 Nov; 46(11):1003-7. PubMed ID: 11762143.
    Abstract:
    OBJECTIVE: To examine the likelihood of twinning through conception during lactation and to attempt to explain why there is an increased sex ratio with monozygotic twinning. STUDY DESIGN: Parturients who had become pregnant while still breastfeeding were asked to supply information about their gestations. Also, records from two maternity services over a three-year period were examined for the sex of monozygotic twin sets. Zygosity was confirmed with the pathology reports of the placentas. RESULTS: Much like that in a previously published study, the sex ratio (females/total) was found to be 0.60 in monozygotic twins. In the case of lactating gravidas, the incidence of twinning was much higher than in a random population (11.4% versus 1.1%). CONCLUSION: These findings are consistent with the model of twinning as a consequence of a depressed calcium environment and its effect on embryonic intercellular bonding.
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