The rate of twin pregnancy is 6 in 1000 births in Japan, 10 in 1000 in the UK and 66 in 1000 in Nigeria. Most of this variation is due to different rates of dizygotic (DZ) twinning. The rate of monozygotic (MZ) twinning is fairly constant at 3–5 in 1000. Triplets occur once in every 6400 births and quadruplets once in every 512 000 births.
KeywordsConstipation Halothane Nigeria Oxytocin Pregnan
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