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This has been produced in consultation with and approved by:. Age affects the fertility of both men and women, and is the single biggest factor affecting a woman? Androgen deficiency in women and its treatment is controversial, and more research is needed. IVF in-vitro-fertilization and ICSI intracytoplasmic sperm injection are assisted reproductive treatment ART procedures in which fertilisation of an egg occurs outside the body.
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Multiple births are more common than they were in the past, due to the advancing average age of mothers and the associated rise in assisted reproductive techniques, in particular the use of fertility drugs. Twins for over 90 per cent of multiple births.
There are two types of twins — identical monozygotic and fraternal dizygotic. To form identical twins, one fertilised egg ovum splits and develops two babies with exactly the same genetic information. This differs from fraternal twins, where two eggs ova are fertilised by two sperm and produce two genetically unique children, who are no more alike than individual siblings born at different times.
Twins are more or less equally likely to be female or male. Factors that increase the odds of having twins Some women are more likely than others to give birth to twins. The factors that increase the odds include: Advancing age of the mother — women in their 30s and 40s have higher levels of the sex hormone oestrogen than younger women, which means that their ovaries are stimulated to produce more than one egg at a time.
of pregnancies — the greater the of pregnancies a woman has already had, the higher her odds of conceiving twins. Heredity — a woman is more likely to conceive fraternal twins if she is a fraternal twin, has already had fraternal twins, or has siblings who are fraternal twins. Race — Black African women have the highest incidence of twins, while Asian women have the lowest.
Assisted reproductive techniques — many procedures rely on stimulating the ovaries with fertility drugs to produce eggs and, often, several eggs are released per ovulation. Fertilisation Hormones secreted by the ovaries, and a small gland in the brain called the pituitary, control the menstrual cycle. The average cycle is around 28 days.
After a menstrual period, rising levels of the hormone oestrogen help to thicken the lining of the womb the endometrium and release an egg from one of the ovaries ovulation. If the egg is fertilised on its journey down the fallopian tube, it lodges in the thickened womb lining, starts dividing and evolves into an embryo. This occurs because the fertilised egg divides in two while it is still a tiny collection of cells.
The self-contained halves then develop into two babies, with exactly the same genetic information. The biological mechanisms that prompt the single fertilised egg to split in two remain a mystery. Approximately one quarter of identical twins are mirror images of each other, which means the right side of one child matches the left side of their twin. These babies will be no more alike than siblings born at separate times. The babies can be either the same sex or different sexes, with the odds roughly equal for each.
It is proposed that the egg splits in two, and each half is then fertilised by a different sperm. This theory is an attempt to explain why some fraternal twins look identical. Gestation for twins The normal length of gestation for a single baby is around 40 weeks. However, gestation for twins, either identical or fraternal, is usually around 38 weeks. Since twins are usually premature, they are more likely to have lower birth weights.
Prematurity is associated with increased risk of a of disorders, including jaundice. Giving birth to twins Childbirth can give rise to complications when just one baby is present, so twins present extra potential for difficulties.
It is advised that women carrying twins give birth in hospital, rather than at home. The babies can be delivered vaginally, but caesarean section delivery may be considered a better alternative in some circumstances. Zygosity testing It is difficult to tell if twins are identical or fraternal at birth. Some identical twins may be born with individual sets of membranes, which may lead to the mistaken assumption that the babies are fraternal. One way to tell the difference is to have the twins DNA-tested.
Identical twins share the same genetic information, while fraternal twins share around half. The test can be done with a sample of cheek cells, collected painlessly. Other tests include blood group examinations. Where to get help Your doctor Paediatrician Maternity hospital Things to remember Twins for over 90 per cent of multiple births. To form identical or monozygotic twins, one fertilised egg ovum splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs ova are fertilised by two sperm and produce two genetically unique children.
Your likelihood of conceiving twins or moreBabyCentre, Inc. More information here. Give feedback about this. Was this helpful? Yes No. View all reproductive system - female. Related information. Content disclaimer Content on this website is provided for information purposes only. Reviewed on:Lonely woman of any age size or race wanted
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