This keeps the lining of the uterus healthy and ready to nourish a developing foetus.
Nor is it likely mothers, whose foetus cannot survive outside, will be allowed to have an abortion.
However, the process stops before it is complete, leaving a partially separated egg which develops into a conjoined foetus.
In pregnancy, it lengthens and becomes a barrier to help retain the foetus.
Scientists generally agree a foetus becomes viable at about 22 to 24 weeks.
However, when pregnant females are infected, the virus can damage the foetus, leading to a range of deformities at birth.
These laws provide harsher punishments or additional murder counts for those whose actions result in the death of a foetus.
Overwhelming them all is a vast painting of an old woman lying curled up like a foetus by Jenny Saville.
ECONOMIST: Maastricht art fair: The party of the century | The
Dermatoglyphics develop at specific times in the foetus at the same time that critical growth in the brain is taking place.
Women will eat soups naturally high in the vitamin, which it is believed may promote lung growth in the developing foetus.
These high lead levels may harm both the mother and developing foetus.
The foetus can also develop problems in the womb, including genetic defects.
Many women fear that, if they cannot eat because of sickness, they will harm the foetus, but research shows this to be unfounded.
To get human retinal cells at the same stage of development, however, would involve taking stem cells from a foetus during the second trimester of pregnancy.
The main source of vitamin D is sunshine and women living in northern latitudes such as Scotland often do not get enough to ensure healthy growth of the foetus.
The judge found the main blame for Kalisha's death lay with the doctor, after he failed to diagnose the pregnancy as ectopic, where the foetus develops outside the womb.
Last month a doctor and his assistant in Haryana were sentenced to two years in jail for revealing the sex of a female foetus and then agreeing to abort it.
But researchers at the Centre for the Developing Brain have found ways to counter the effects of these movements, building up full three-dimensional pictures while the foetus is in motion.
BBC: Babies' brains to be mapped in the womb and after birth
Both the 12-week and 20-week laws include exemptions for rape, incest, and cases when the mother's life is in danger or the foetus is diagnosed with an extremely serious disorder.
To minimise the possibility of the foetus developing spina bifida, woman are advised to take folic acid supplements in the months leading up to conception and the first three months of pregnancy.
The draft report on the death of Savita Halappanavar has found an over-emphasis by medical staff on the welfare of the foetus, which was unviable, a solicitor for her widower Praveen has said.
Nearly every day, he sat at the back of Galway court house and listened to the details of his wife's last days, and her miscarriage of their 17-week-old female foetus, a much-longed for child.
The agents prescribed to counteract these effects are both expensive and only partially effective, and cannot be given to women who might want to become pregnant, because they are harmful to the developing foetus.
But medical technology has also pushed earlier and earlier the age at which a foetus becomes viable outside the womb, putting abortions even in the second three-month term of pregnancy on shakier moral ground.
ECONOMIST: Raising the stakes in the battle over abortion | The
However, I think the worrying trend towards the commercialisation of pregnancy and trend in "foetus parties" can add to the burden and can increase the expectation for mothers which midwives then have to deal with.
Most countries in the region - where Roman Catholicism is a dominant force - allow abortion only in cases of rape, when the woman's life is in danger or if the foetus is severely deformed.
The authority said that its audit had found that the council form and NHS form used to apply for the cremation of a non-viable foetus (children born up to 23 weeks and six days gestation) were inaccurate.
But Dr Mary Favier, said the expected legislation does not go far enough and not just because it does not allow for abortion in cases of rape, incest or where the foetus cannot survive outside the womb.
BBC: Battle between anti-abortion and pro-choice campaigners
The US tradition of having a baby shower to celebrate an impending birth is now commonplace in the UK. But "foetus parties", where people gather to view 3D and 4D scan pictures are also gaining in popularity.
It appeared to be the genes passed on to the mouse foetus that made all the difference - if a mouse could produce enough G6PD, it tended to survive, even when carried by an enzyme deficient mother.
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