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The rise in preterm
births
According
to 1996 Health Canada statistics, preemie rates
in this country went up to 7.1 per 100 births
in 1996 from 6.4 in 1981. More recent figures
from the 2000 Canadian Perinatal Health Report
show that by the turn of the century, that figure
had crept up to 7.5.
The
boost in preterm birth rates is due to many factors,
including the increased survival rate of preterm
babies thanks to improved ultrasound technology
and other early obstetric interventions.
Even
though preterm births are seen as one of the industrialized
world's most significant perinatal health problems,
current comparative data is hard to find. Canadian
rates mirror those of other industrialized countries
with the striking exception of the US, where the
rate was 11%.
The
very high US rate could be explained by the marked
differences in preterm birth rates between non-Hispanic
whites and non-Hispanic blacks — 17.4% of
live births to black women were preterm versus
9.8% for whites.
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Preterm babies have always faced
greater health problems. A new Swedish study published
in the November 29 issue of Circulation indicates
that for men born prematurely, the risks of high blood
pressure later in life skyrocket.
Sweden and Canada have a similar
percentage of preterm births — roughly 7%. "In
this study, preterm birth was identified as a new and
very early risk factor for high blood pressure," explained
neonatologist Dr Stefan Johansson, the study's lead
author from Karolinska University Hospital in Stockholm.
Study participants were predominately
Caucasian and Nordic born. The study involved an impressive
329,495 men born between 1973 and 1981; their blood
pressure was measured when they were drafted for military
service between 1993 and 2001.
STAGGERING
FINDINGS
"The association between preterm birth and high blood
pressure is unlikely to be explained by family history
or genetic factors," observed Dr Johansson. "Instead,
early environmental challenges faced by the premature
baby may affect development permanently, contributing
to higher blood pressure in adulthood."
The figures are staggering. Compared
to full-term babies (37-41 weeks), extremely preterm
(< 29 weeks) had almost twice the risk of high systolic
blood pressure. Men considered very preterm (29-32 weeks)
had a 45% increased risk; the moderately preterm (33-36
weeks) had a 24% risk. (High BP was defined as systolic
pressure of 140mm Hg or greater and diastolic pressure
of 90 mm Hg or greater.)
Additionally, babies born small
for their gestational age showed a 10% increased risk
of high systolic BP versus those born at normal weight.
According to Dr Johansson, this
is the biggest study of its kind and includes subjects
who were born during evolving neonatal care. Most studies
which link low birth weight to cardiovascular diseases
were based on participants who were born at a time when
most very preterm babies died.
Dr Robert Usher, neonatologist
at Mont-real's McGill University Health Centre, agrees,
saying he's impressed both by the scope and design of
this largescale study. "It's the first major study based
on gestational age rather than low birth weights," he
said.
Dr Johansson added that the study's
findings are important in that they offer preterm men
a chance to act early. "I believe that very preterm
born children should have their blood pressure checked
during their clinical follow-up programs," he said.
"It may also be even more important for people born
preterm to have a healthy lifestyle and to manage known
risk factors of cardiovascular disease, such as smoking."
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