Babies born just slightly prematurely have more health problems than those born at full term, US researchers say.
Researchers looked at babies born just a few weeks early
They found conditions such as jaundice and hypoglycaemia were more common in babies born at 35 or 36 weeks gestation than those born at 37 weeks or more.
The Massachusetts General Hospital team challenged the assumption near-term babies did as well as full-term.
Writing in the journal Pediatrics, they said women should not bring delivery forward believing it would do no harm.
Researchers compared the health of 95 babies who were born full-term - at 37 or weeks or more - with 90 babies born at 35 or 36 weeks gestation.
They found that the premature babies were significantly more likely to have health problems. Eighteen had multiple ailments, while none of the full-term babies had more than one problem.
Hypoglycaemia - low blood sugar - was three times as common among near-term babies compared with full- term.
Just over half of near-term babies were jaundiced, compared with 37.9% of full-term.
Among the problems suffered by the near-term babies were jaundice, hypoglycaemia, respiratory distress, the need for intravenous feeding and difficulty maintaining body temperature.
The researchers added that premature babies often required different and more expensive treatment to those born at full term.
Dr Marvin Wang, who led the research, said: "Conventional wisdom has been that babies who were near-term, but still premature, would do as well as full-term babies.
"But those of us who take care of these children know from experience that they may have more jaundice or hypoglycaemia than full-term infants do."
They noted that some mothers schedule planned Caesarean deliveries before their due date to avoid muscle tearing or stretch marks, or to better suit their schedules or those of their doctors.
The researchers added: "There can be valid medical reasons for delivering early, but our study calls into question the presumption that elective delivery at 35 or 36 weeks poses no risk to the infant."
Peter Soothill, Professor of Maternal and Foetal Medicine at the University of Bristol, said the problems experienced by near-term babies could have been linked to pregnancy complications that led to the early delivery.
He said: "For example, women may have ruptured membranes, infections in the pregnancy, foetal growth restriction or too much amniotic fluid, all of which may result in a baby being born a little early, either spontaneously or because of the actions of obstetricians.
"Those complications in pregnancy would also increase the chance of the neonatal problems that are being described, so without much more information
about the pregnancies, it does not seem to be possible to separate neonatal problems due to being born a little early from those due to the cause of being born early."
Professor Soothill added: "Spontaneous onset of labour and delivery at term (38-41 weeks) should be the goals for pregnancy whenever possible.
"However when early delivery is clearly needed for an important indication, people should not be too scared because with modern neonatal care the vast majority of these babies will be fine."