Tuesday, December 1, 2009

How Many Preemies Does it Take?

by Melissa Avery, CNM, PhD, ACNM President

As National Prematurity Awareness Month closes, we’re digesting a lot of statistics. Today, in the US, more than 1,400 babies will be born prematurely. Between the early 1980s and 2006, the rate of premature birth rose by 36%. These are fascinating and disturbing statistics, but as a midwife who is actively engaged in research, there is one companion statistic that startles me even more: From 1992 to 2002, the average gestational age at birth in the US dropped from 40 weeks to 39 weeks.

It does not take a statistician to appreciate that a drop in the average time a baby is born by a full week over the course of just 10 years means something big has been happening. Over 4 million babies are born each year in the US. A substantial increase in the rate of prematurity would be needed to reduce the average time of birth by a full week.

Why the rise in prematurity despite advances in medical knowledge and technology? According to the most recent March of Dimes prematurity summit, the primary reason is not obesity or smoking, as you might expect—it’s labor induction. In 1990, the rate of inductions was 9.5%. By 2006, the rate more than doubled to 22.3%.

Research documents that preterm infants have an increased risk of being admitted to level 2 or 3 nurseries and that important brain development continues all the way to full-term. More recently, late preterm infants (born at 34-37 weeks gestation) have been shown to have a 30-fold increase in complications like respiratory problems, hypoglycemia, and hypothermia.

Certified nurse-midwives and certified midwives have a long history of reserving labor induction for the situations when it is absolutely necessary. The American College of Obstetricians and Gynecologists (ACOG) recently issued a statement calling for an end to inductions prior to 39 weeks unless there is a clear medical indication. Now that the US has enough preemies to impact a national statistic and a national medical organization, let’s support a re-examination of medical indications for labor induction prior to full-term and promote a renewed emphasis on waiting for spontaneous labor and birth.

1 comment:

Kathy said...

I think the "average gestational age at birth" is not the statistical mean, or what the common person thinks when using the term "average," like averaging grades for a report card; but rather the "mode" -- the most common time of birth. I checked out the CDC Wonder linked birth-death records for 2005, and it said that just over 1 million babies were born at 39 weeks in 2005, which was the most common week to be born (the mode). There were fewer than half a million babies born between 20-36 weeks; about 350,000 babies born at 37 weeks; 700,000+ in 38 weeks; just over 800,000 at 40 weeks, and between 3-400,000 for both 41 weeks and 42w+.

But I can't figure out how to perform the statistical function to figure out what it would take to shift the "average" (i.e., the mean, or the median, for that matter) to a week before. However, there are two different things that could affect the results: 1) more babies being born preterm or in early term accidentally or iatrogenically; and 2) fewer babies being allowed to go past 40 or 41 completed weeks of gestation. Both of these together might have an effect on the mean; but refusing induction/C-section to 100,000 moms at 39w and allowing it at 40w or after would switch the mode back to 40 weeks.

-Kathy @