Nakamura I, Harada C, Miura T
Japan Women's College of Physical Education, Tokyo.
Acta Genet Med Gemellol (Roma). 1993;42(3-4):295-7. doi: 10.1017/s0001566000003305.
The distribution of menarcheal interval-length between cotwins in 67 pairs of female identical twins in Tokyo was found to cluster at fairly constant intervals. When delayed in one twin, the menarche occurred in the second twin at intervals of approximately 28 days after that of the earlier twin. This finding suggests the existence of a latent lunar or menstrual cycle in pre-menarcheal girls, evidence for which was detected by recording the menarcheal intervals between MZ cotwins in days.
