The pregnancy 'bloom' really exists because carrying a baby has a 'rejuvenating effect' on women, say scientists.
Pregnancy helps regenerate tissue and slow down the ageing process because expectant mums share their unborn child's blood.
Medical experts for the journal Fertility and Sterility said appearing to bloom is not just a cosmetic side effect of carrying a child, but an actual physical process.
They studied the effects of liver transplants on pregnant and non-pregnant mice using a high-tech MRI scanner at the Hadassah Medical School in Jerusalem.
It found in young, non-pregnant mice, 82 per cent of the liver had regenerated after two days and in older, non-pregnant mice, only 46 per cent had regenerated in that time.
But in older pregnant mice, around 96 per cent had regenerated after two days, better than the non-pregnant rodents both young and old, they reported.
They also found that pregnancy protected the rodents from tissue damage around the heart, which is also an irreversible part of the human ageing process, said the study.
Pregnancy is a unique condition for the human body, said the researchers, and as a result it has to cope with two people's systems at the same time.
For the older of the two bodies, it is as if it has been injected with a youth serum from the baby it is carrying, hence the rejuvenating process affecting the mother, it suggests.
The report added: "As we age, it is more difficult for our tissue to regenerate itself.
"Because pregnancy is a unique biological model of a partially shared blood system, we have speculated that pregnancy would have a rejuvenating effect on the mother."