Will My Baby Catchup? Growth and Prematurity

A summary of scientific studies on growth of preemies : catch-up growth can continue into adolescence, and the majority of tiny premature infants should be normal sized adults.

By Dr. Raye-Ann deRegnier

Many parents of premature infants have concerns about their child's growth - before and after discharge from the NICU. For some families, these concerns can linger well into childhood and can lead to worries of permanent stunting of growth. This article describes factors that are associated with small size or poor growth in premature children. Phases of growth beginning from birth will also be discussed. Lastly, new studies on catch-up growth are summerized.

Prenatal Influences on Growth

There are several factors besides prematurity which may affect size at birth and growth after birth. Two important factors are size of the parents and Intrauterine Growth Retardation (IGR).

Tall parents tend to ultimately have tall children and vice-versa. Women weighing less than 100 pounds are at increased risk to have a premature infant, and those women might also be genetically endowed to have a small child.

Intrauterine growth retardation is a condition in which infants grow slowly before birth. This can occur with toxemia of pregnancy (also called pre-eclampsia). It also is very common in twins, triplets and higher order multiples. In the case of multiples, it may be due to unequal placental separation or from blood vessel connections between twins.

Prematurity Related Issues

We know that infants weighing more than 1500 grams at birth usually do not have a lot of problems with growth later. (Infants who are severely undersized for their degree of prematurity may be exceptions.)

However, infants born >extremely prematurely are tinier at birth and tend to be sicker. Sicker babies are harder to nourish properly at first. They may not tolerate the IV (intravenous) nutrition and may be harder to feed. They lose weight early on (much of this is water weight, but some is actual body mass). Finally by the time they are two to three weeks old, they have regained their birthweight, but may grow quite slowly for some time.

If a premature infant in the hospital does not grow, or grows more slowly than usual, they will start to fall off the growth chart. Babies in utero tend to grow very rapidly during the last trimester and it is very hard to get a premature infant to keep up with this pace if he or she is sick.

If a premature infant starts out small (because of intrauterine growth retardation) and is then sick, it will not take long until the child is far below the growth chart. Luckily, the phase of slow growth does not last forever and soon the baby is able to put on weight as fast as a baby in utero (1/3-1 ounce per day is usual in utero).

Phases of Growth

When this faster growing phase begins, the first growth goes to the baby's head (brain growth is prioritized), next it goes to the weight (usually) and lastly to the length. This gives the premie different body proportions compared with a term baby.

At this phase, the infant or child is growing as fast as a term infant. This is great, and will help reverse any nutritional deficits.

Catch Up Growth

However, for the child to become the same size as his or her full term peers, growth will have to be faster than usual. This is called "catch-up growth".

85% of premature infants have catch-up growth and land on the regular growth chart by two years of age.

An article in the Journal of Pediatrics (June, 1998) describes adolescent growth of 32 extremely premature children from birth through 12-18 years. All weighed less than 1000 grams at birth. The study found that by 12-18 years of age, only 6% of the children were below the normal range for height, and these children had mothers who were short themselves

A few other studies have looked at long term growth. These studies have shown 16-28% of children are still below the normal range at 8-16 years of age. The variability between these studies is most likely due to the small numbers of children in the studies, and most likely the differing nature of the populations of children born in different NICUs.

Delays in Catch Up Growth

Some common reasons a child may not catch up fully by two years of age are:

1. Starting out very far below the growth chart with a long, long way to catch up.

2. Ongoing problems which increase the nutritional requirements.

Some babies (but not all) with BPD or chronic lung disease may have an increased metabolic rate and need more nutrition than other infants. Unfortunately, it can be very difficult for these little guys to eat as much as they need to eat. This increased metabolic rate can also last for a long time after discharge.

Another potential ongoing problem is illness and a reduction in feedings as a result.Some children with cerebral palsy also have higher metabolic rates. There are other ongoing problems which might apply, as well.

3. Poor appetite.

Some children never develop a hearty appetite and may need to be reminded to eat, even as they get older. Some children get very active and forget to eat or just like to snack.

Well, what about the kids who don't catch up by 2 years of age? Some of them will slowly catch up at their own pace. What we don't know is if all of those children will catch up if you just give them long enough.

The bottom line is that catch-up growth can continue into adolescence, and the majority of tiny premature infants should be normal sized adults.

Dr. Raye-Ann deRegnier is an attending neonatologist at Children's Hospital of St. Paul and Director of the NICU Follow-up Clinic. She is also an Assistant Professor of Pediatrics at the University of Minnesota.