Researchers from the University of Auckland found that sleeping on your back during pregnancy results in a baby with slightly less body weight than if the mother preferred to sleep in a different body position.
The study involved 1760 pregnant women who are at least 28 weeks pregnant. Scientists observed them until the moment of birth.
Of these, 57 (3.2%) reported that they slept on their back during the last 1–4 weeks before giving birth. The average weight of children born to them was 3.41 kg, while the average weight of babies born to women who slept on their side was slightly higher — 3.55 kg.
Although in both cases the weight of the children was within the normal range, nevertheless, scientists indicate that there is a difference, and it is statistically significant. This may be because sleeping on your back during the third trimester of pregnancy puts pressure on the superior vena cava, which returns blood from the head to the heart, and on the aorta, which carries blood to the rest of the body. Thus, the volume of blood ejected by the woman’s heart decreases, which causes a decrease in blood flow to the uterus and thereby limits the growth of the baby.
It has also been previously shown that there is an association between an increased risk of stillbirth and sleeping on your back. The increase in risks in this case is also very insignificant, but it exists. Therefore, many obstetrician-gynecologists recommend that expectant mothers sleep on their side at the end of pregnancy.