What happens if more than one sperm

The only other reported instance of so-called sesquizygotic twins was identified in They were brought to the attention of doctors because one had ambiguous genitalia. To see if the phenomenon might be more common than doctors believed, the Gabbett team examined an international database of fraternal twins and their parents. None showed the same pattern.

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.

Number of previous pregnancies — the greater the number 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 number 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 best to check with your physician to see which method was used to assess sperm shape and the significance of the results.

Yes, it can. However, having higher amounts of abnormally shaped sperm has been associated with infertility in some studies. Usually, higher numbers of abnormally shaped sperm are associated with other irregularities of the semen such as low sperm count or motility.

Men with abnormally shaped sperm may also have no trouble causing a pregnancy. Once the sperm enters the egg, fertilization has a good chance of taking place. No one is sure why the sperm shape matters.