Editing Multiple birth (section)

===Quadruplets===
Quadruplets are much rarer than twins or triplets. As of 2007, there were approximately 3,556 sets recorded worldwide. Quadruplet births are becoming increasingly common due to [[fertility treatment]]s. There are around 70 sets of all-identical quadruplets worldwide. Many sets of quadruplets contain a mixture of identical and fraternal siblings, such as three identical and one fraternal, two identical and two fraternal, or two pairs of identicals. One famous set of identical quadruplets was the [[Genain quadruplets]], all of whom developed [[schizophrenia]].<ref>{{Cite journal |last1=Mirsky |first1=A. F. |last2=Delisi |first2=L. E. |last3=Buchsbaum |first3=M. S. |last4=Quinn |first4=O. W. |last5=Schwerdt |first5=P. |last6=Siever |first6=L. J. |last7=Mann |first7=L. |last8=Weingartner |first8=H. |last9=Zec |first9=R. |last10=Sostek |first10=A. |year=1984 |title=The Genain Quadruplets: Psychological studies |journal=Psychiatry Research |volume=13 |issue=1 |pages=77–93 |doi=10.1016/0165-1781(84)90120-3 |pmid=6151205 |s2cid=43234604}}</ref>  Quadruplets are sometimes referred to as "quads" in Britain.<ref>{{Cite OED|quad}}</ref>
<!-- COMMENTING OUT CONFLICTING STATS - CHECK SOURCES Two genetically-different sets of identical twins statistically make up half of all quadruplets. Approximately 95% of quadruplets are all fraternal. -->