The problem is that women see in what they do that it ensures the stability of the fetus, which is sleeping on the back, but this method of sleep may have risks to the weight of the fetus, similar in effect to the effect of smoking 10 cigarettes.
A scientific study has shown that the sleep of a pregnant woman on her back, may affect the weight of the fetus.
The study was conducted by the University of Auckland, the United States, subjected to 1760 pregnant women from different countries, including: New Zealand, Australia and Britain.
The results of these pregnant women were studied and analyzed after the 28th week of pregnancy.
According to the study, 57 women surveyed said they were lying on their backs during the last one to four weeks of pregnancy.
These women were three times more likely to give birth to a young child in relation to gestational age.
The study found that pregnant women who start to sleep on their backs in the last week to four weeks of pregnancy, were three times more likely than others to have a child a smaller size, compared to the gestational age, and was lower than the average by 144 grams.
Scientists explain that sleep on the back reduces the flow of blood to the placenta and fetus, because the compression of a major blood vessel in the mother's abdomen because of the large size of the uterus in that period of pregnancy.
The study found that the 10 percent births of the least weight, are more likely than others to be born deceased or have health problems before and after birth.
Doctors are advised to sleep on both sides in this period of pregnancy, as it has additional benefits in improving the weight of the baby at birth.