The city of Kirov in north-eastern European Russia is fast becoming famous for its unusual rate of twin births. According to medical statistics, approximately one out of 89 births is a twin couple. As for triplets, they are born in every 7 000-10 000 couple. After taking a stroll through one of the Kirov's districts, Prava reports, one can easily begin doubting the statistics. The city’s population barely reaches 500 000 and identical couples (or even triplets seem to be everywhere). http://english.pravda.ru/science/19/94/377/14784_twins.html
For reasons that are not yet known, the older a woman is the more likely she is to have a multiple birth naturally. It is theorized[ that this is due to the higher level of follicle-stimulating hormone that older women sometimes have as their ovaries respond more sluggishly to FSH stimulation.
Russian scientists are hypothesizing that the increase in twin births In Kirov may be related to strong electromagnetic interference in the region which is affecting cell division at an early stage of fetal development. “It is possible that some kind of electric field had its affect on such high multiple birth rate in the town,” presumes chair of biology and genetics at Kirov’s medical academy Alexander Kosykh. “Any biological cell has its own electric charge and its own polarity. That is why, it is quite possible that strong electromagnetic field in this particular district somehow affects genetic processes. However, we cannot make any definite claims yet.”
Other possible explanations cannot be excluded. During the Second World War, biological weapons development was based in Kirov under the Stalinist-Soviet era. CIA documents suggest that Kirov was, in fact, the principle BW research center in the USSR during the Cold War. Environmental contamination is, therefore, a possibility. http://www.faqs.org/cia/docs/93/0000250910/THE-SOVIET-BW-PROGRAM.html
Kirov is not the only town with such strange occurrences. Another “factory of twins” exists in Nigeria in a small town Igbo-Ora situated not far from Ibadan.
Studies in the Nigeria case suggest that the unusual incidence of twin births among the Yoruba people -a large Nigerian ethnic group- may be related to environmental factors, namely diet.
Central to the Yoruba people's diet is the cassava, a plant with a tuber root, which can be eaten in addition to the leaves and flowers. Research into multiple births carried out at Lagos's University Teaching Hospital has suggested that a high level of a chemical found in the Yoruba women and the peelings of the tuber could account for the high level of multiple births.
According to local doctors:
'Numerous works has shown that the tuber food of the Yoruba women, especially the peelings, contains a very large amount of these chemical substances. These women have a disproportionately large amount of these chemicals in their system and this encourages the release of more than one egg. There is enough reason to believe in this theory.' http://www.bbc.co.uk/worldservice/people/highlights/010607_twins.shtml
Other researchers remain skeptical to the diet theory.