Babies born by in vitro fertilisation (IVF) do not face an increased risk of birth defects, nor are they at greater risk of being smaller than normal. But the researchers did find that women pregnant via IVF were more likely than those who conceived naturally to develop a pregnancy complication called placenta previa, in which the placenta blocks the opening to the birth canal.

Some studies comparing babies born through IVF and those conceived naturally have found worse outcomes for the IVF infants, including higher rates of birth defects and greater likelihood of low birth weight. To assess perinatal risks to singleton births after in vitro fertilisation (IVF) versus spontaneous conception, the researchers studied 53,939 singleton births from spontaneous conceptions and 1,408 singletons after IVF, all from Japan.

Just 23 of the IVF babies died as newborns, such a small number that the researchers were unable to gauge whether or not IVF increased infant death risk. About one in five IVF babies were low birth weight, compared to about one in six naturally conceived babies (the control group), but the difference was no longer statistically significant after the researchers adjusted for mother's age, baby's gestational age at birth, and other factors.

About 2 percent of both the IVF babies and the control group infants had birth defects. While there is some evidence that IVF is linked to certain types of birth defects, the researchers note, the current study did not include specific information on the malformations infants had. Both groups of babies were at similar risk of being born small for gestational age, while the ratio of boys to girls born was the same in the IVF and the control group.

These findings offer no evidence that IVF babies are more likely to have problems than naturally conceived infants. However, 5 percent of women who became pregnant via IVF developed placenta previa, compared to 1.5 percent of the women who conceived naturally. Placenta previa is a complication that occurs in the second or third trimester of pregnancy, which can lead to heavy vaginal bleeding and interfere with the birth process.