Specific Learning Objectives: Explain how multiple births occur Specific Learning Objectives: Explain what happens when a baby is born

The New Zealand Multiple Birth Association Incorporated is the national body representing 22 local Multiple Birth clubs consisting of over 1500 families throughout New Zealand. There were almost 900 sets of twins and triplets born last year in New Zealand, and 11 sets of triplets were born to new mothers (from the 2009 census). In 2009, 161 mothers who gave birth to twins or triplets already had at least two other children. We aim to provide education and support to all of these families, through providing guidance and resources to their local multiple birth club.

Multiple Pregnancy - The Basics There are two main types of multiple pregnancy: Fraternal – two or more eggs, fertilised separately. The mother releases two eggs and both become fertilized by two different sperms. Twins can be the same sex, or different sexes. Identical –– one fertilized egg, which splits after conception. Identical twins are always the same sex and share the same genes. The biological mechanisms that prompt the single fertilized egg to split in two remain a mystery! Identical twins share the same DNA - but do not have identical DNA. When the egg splits into two halves to form identical twins, the DNA may not divide equally between the two cells. The basic concept is similar to when you cut an apple in half, the two halves may not look the same.

Studies show that there is a genetic basis for fraternal twinning ;that is, non-identical twins do run in families. However, it is only the female that has any influence on the chances of having fraternal twins as the male cannot make her release more than one ovum. Your likelihood of having fraternal twins is dependent upon the woman carrying a fraternal twin gene and can also be affected by heredity, race, marital age and number of children previously born. Two-thirds of all twin births result in same sex fraternal twins and one-third are different sex fraternal twins. About two-thirds of all twin births are fraternal.

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