It's already known that premature babies are at risk for developmental issues as they grow. But for babies born on time, how much difference does one or two weeks make?
A recent study sought to find the answer to that question. A baby born "at term" is born any time between 37 and 41 weeks.
Researchers wanted to know whether it made a difference how early or late a baby was born within that window. They found that it does make a slight difference if a baby is born on the early side.
Each extra week in the womb offered a slight benefit on developmental scoring when the children were 1 year old.
The study, led by Olga Rose, MD, of the Department of Pediatrics at Massachusetts General Hospital with Harvard Medical School, looked at the development of children born between 37 and 41 weeks.
The researchers included 1,562 babies who were born between the 37th and 41st weeks of pregnancy and were at least 6 pounds, 9 ounces at birth.
The children's mental and motor skills were assessed when they were 1 year old. The researchers then calculated into their findings any differences between the children related to birth weight, gender, socioeconomic status and their home environment.
The children were also part of a study on iron deficiency, so the researchers also took into account whether the children were receiving iron supplements and their iron blood levels.
The researchers used an assessment called the Mental and Psychomotor Bayley Scales of Infant Development. This assessment is similar to an IQ test for babies and toddlers.
The average score for a typical child with typical development on this scale is 100. A baby with a score 15 or more points above this is above average. A baby with a score 15 or more points below 100 is below average.
The researchers found that each additional week of pregnancy before a child's birth was linked to an increase of 0.8 points on the Mental Development Index assessment they used.
Each additional week of pregnancy before birth was also linked to an additional 1.4 points on the Psychomotor Development Index. These associations remained after the researchers took into account the other differences between the children.
The differences are very small in looking at the range of development. However, they could not be explained by chance.
"There is increasing evidence that birth at 39 to 41 weeks provides developmental advantages compared with birth at 37 to 38 weeks," the researchers wrote.
"When [single baby] pregnancies are proceeding without identified risk to the mother or fetus, prioritizing timing of delivery for 40 to 41 weeks would allow more time for in utero brain development leading to more optimal developmental outcomes," they wrote.
According to Kurian Thott, MD, FACOG, an OBGYN at Women's Health and Surgery Center in Washington, DC, this study supports the advice OBGYNs have told patients for many years: "do not rush mother nature."
"It can be very uncomfortable in the final few weeks of pregnancy, and it is not uncommon for patients to ask their doctors to help alleviate their discomfort with a planned induction or earlier delivery," Dr. Thott said. "Doctors sometimes feel compelled to satisfy their patients desires in hopes of keeping patients happy."
He said this study is important for helping OBGYNs explain to patients the importance of waiting until the baby is ready to arrive.
"That one to two weeks can make a world of difference and can help their newborn reach those important developmental milestones," Dr. Thott said. "Hospitals are also becoming more proactive in this respect by monitoring and asking for verification from the provider that a delivery before 39 weeks is medically justified."
However, Dr. Thott added that the situation may be different for women who have pregnancy complications.
"This study, of course, only applies to those pregnancies that are uncomplicated as there can be many clinical scenarios in which a delivery before 39 weeks is required," Dr. Thott siad. "This study also gives patients an opportunity to ask their doctor why they would need to be delivered sooner and if their pregnancy is at risk for this."
The study was published April 15 in the journal Pediatrics. The research was funded by the National Heart, Lung and Blood Institute and the National Institute of Child Health and Human Development. The authors declared no conflicts of interest.