Unpredicted ovulations and conceptions during early pregnancy: an explanatory mechanism of human superfetation
Juan J. Tarín A E , Miguel A. García-Pérez B , Carlos Hermenegildo C and Antonio Cano D
+ Author Affiliations
- Author Affiliations
A Department of Functional Biology and Physical Anthropology, Faculty of Biological Sciences, University of Valencia, Burjassot, Valencia 46100, Spain.
B Research Unit-INCLIVA, Hospital Clínico de Valencia and Department of Genetics, Faculty of Biological Sciences, University of Valencia, Burjassot, Valencia 46100, Spain.
C Research Unit-INCLIVA, Hospital Clínico de Valencia and Department of Physiology, Faculty of Medicine, University of Valencia, Valencia 46010, Spain.
D Department of Pediatrics, Obstetrics and Gynecology, Faculty of Medicine, University of Valencia, Valencia 46010, Spain.
E Corresponding author. Email: tarinjj@uv.es
Reproduction, Fertility and Development 25(7) 1012-1019 https://doi.org/10.1071/RD12238
Submitted: 19 July 2012 Accepted: 11 September 2012 Published: 9 October 2012
Abstract
In this bioessay, a literature review on human superfetation was performed in order to find epidemiological variables associated with this phenomenon. Thereafter, an explanatory mechanism of superfetation compatible with the endocrinological, histological and physiological changes undergone by women during early pregnancy is proposed. Superfetation can be defined as the ovulation, fertilisation and implantation of a second or additional embryo(s) during pregnancy. The literature review evidences a small discordance in gestational age between dizygotic twins in humans (range: 2–4 weeks; mean ± s.e.m.: 3.3 ± 0.3 weeks). This difference is compatible with a luteal out-of-phase (LOOP; i.e. atypical increase in E2 levels in the mid-luteal phase)-like event occurring between 1 and 3 weeks after the ovulation that allowed the first pregnancy to take place. The LOOP-like event may allow passive sperm transport from the vaginal fornix to the Fallopian tube ipsilateral to the ovulatory ovary and trigger a LH peak and ovulation. Furthermore, during very early pregnancy, the decidual reaction is not yet completed and at least one proximal Fallopian ostium may be opened, allowing the passage of the spermatozoa ascending to the fertilisation site and the extra embryo(s) descending to the implantation site(s).
Additional keywords: decidual reaction, luteal out-of-phase event, peristaltic uterine contractions, very early pregnancy.
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