Hello rhesley-ga,
Thank you for a most interesting -- and troubling -- question.
The source you referenced at the Center for Maternal Fetal Medicine:
http://www.lvpa.com/articles/fibronectin.htm
notes that: "Over one million episodes of preterm labor occur
annually in the United States..."
While this figure strikes me as on the high side, it is not wildly so.
Preterm labor/preterm birth is a serious -- one is tempted to say,
epidemic -- problem in the United States, and one that has resisted
public health efforts to reduce the overall incidence.
I will detail some of the key sources of information on preterm labor
and preterm birth in my answer, below.
If any of the information is not clear, or if you need additional
information, just let me know by posting a Request for Clarification,
and I'll be happy to assist you further.
pafalafa-ga
==========
The bottom line:
There were 480,812 preterm births in the United States in 2002.
Preterm births are defined as births occurring before 37 full weeks of
gestation (a more detailed, clinical definition is given below).
This was 12.1% of the total of 4,021,726 births that year -- a high
rate that has been increasing in the past few decades.
The actual number of women experiencing preterm labor is not known,
and has never been well-documented or even reliably estimated. With
almost half a million preterm births occurring (not all of which are
associated with preterm labor), it seems unlikely that there are
double that number of women experiencing preterm labor episodes
serious enough to require urgent medical attention. However, I
wouldn't dismiss the one million figure entirely -- it does seem to be
within the range of possibility, albeit at the high end of the range.
==========
The most authoritative source of information on the prevalence of
preterm births in the US comes from the CDC's National Vital
Statistics series of reports:
http://www.cdc.gov/nchs/data/nvsr/nvsr52/nvsr52_10.pdf
National Vital Statistics Reports
Vol. 52, No. 10, December 17, 2003
Births: Final Data for 2002
What follows are some excerpts from the report, with my own added
comments in brackets:
--There were 4,021,726 live births in 2002,
--Preterm delivery is a leading cause of neonatal mortality and
birth-related morbidity.
-- Influenced in part by the rising rate of multiple births (multiples
are more likely to be born early), the proportion of preterm infants
has risen 14 percent since 1990.
--The steep rise in multiple births over the past two decades has had
an important influence on the overall preterm birth rate...twins,
triplets, and higher order multiples are much more likely to be born
earlier than singletons
[Most observers consider the increase in twins, triplets and other
multiple births to be a key contributor to the rising rate of preterm
births]
--The preterm birth rate increased again in 2002, to 12.1 percent of
all births, from 11.9 percent in 2001.
--The proportion of infants born preterm...has risen 14 percent since
1990 (10.6 percent) and 29 percent since 1981 (9.4 percent).
[Hard to believe that our health care system has taken such a large leap backwards]
--The bulk of the rise for 2001-2002 was for moderately preterm
births, that is, infants born at 32-36 weeks; the percent of infants
born very preterm (less than 32 weeks) was essentially unchanged at
1.96 percent.
--The overall rate for tocolysis, the use of agents that inhibit or
delay uterine activity for the management of preterm labor, was 2.1
percent in 2001 and 2002. The rate of tocolysis has been fairly stable
since 1996. Discussion on the safety and efficacy of these agents is
ongoing.
[About 2.1% of pregnant women experiencing preterm labor are treated
with drugs intended to minimize the likelihood that the episode will
result in preterm birth.
--Unfortunately, meaningful reduction in preterm births is unlikely
until its causes are better understood.
--[The report includes a detailed table of the number of births and preterm births]
Table 43. Live births by birthweight and percent very low and low
birthweight, by period of gestation and race and Hispanic origin of
mother: United States, 2002
All births -- 4,021,726
Total under 37 weeks -- 480,812
Under 28 weeks -- 29,425
28-31 weeks -- 48,420
32-35 weeks -- 224,364
36 weeks -- 178,603
[Of the total of 480,812 preterm births, the greatest number occur
relatively late in the preterm period (32 weeks and beyond), which
greatly reduces the likelihood of mortality or complications for the
infant. Earlier preterm births experience the bulk of the medical
problems.]
==========
Another extensive government sponsored study that sheds additional
light on the topic of preterm labor and births is the "Management of
Preterm Labor" report:
http://www.ahrq.gov/clinic/epcsums/pretermsum.htm
Agency for Healthcare Research and Quality
Evidence Report/Technology Assessment: Number 18
Management of Preterm Labor
The report at the link above is the Executive Summary, but the full
report can be downloaded by clicking on the link at the bottom of the
Executive Summary.
The excerpts below are from Chapter 1 of the full report, which
summarizes the information known -- and not known -- about the extent
of preterm labor:
==========
Overview and Burden of Disease
--Although preterm labor is the most common cause of antenatal
hospitalization, the number of pregnancies in which preterm labor
occurs is documented inadequately.
--the number of...pregnancies in the United States affected by the
occurrence of preterm labor that do not result in preterm birth has
not been projected accurately.
[This theme is repeated throughout the report -- the actual number of
preterm labor episodes is simply not known, nor is there
reliable-enough data to even allow for a good educated guess]
--research criteria for diagnosis of preterm labor: "contractions
occurring between 20 and 36 weeks' gestation at a rate of four in 20
minutes or eight in 1 hour with at least one of the following:
ruptured membranes, cervical change over time, dilatation 2.0 cm, or
cervical length 1.0 cm."
[This is apparently the most widely-used clinical definition, though
for most purposes, simply saying "earlier than a full 37 weeks" is
more than adequate]
--No consensus exists regarding the diagnosis or the treatment of
preterm labor. Approaches range from essentially "watchful waiting"
or traditional "conservative interventions" (e.g., bed rest) to
complex diagnostic and therapeutic regimens involving biologic marker
tests (diagnosis) and pharmacologic agents (antibiotics, tocolytic
drugs and perhaps corticosteroids) and to system-wide (e.g., state or
county) programs to detect and manage the condition
--Preterm labor afflicts pregnant women of every socioeconomic class,
and ethnic group, and age.
--Preterm labor can be addressed in clinicians' offices, private and
public inpatient and outpatient settings, free-standing birth centers,
and patients' homes.
--The morbidity for babies born preterm can manifest in many ways.
Short-term outcomes for newborns can include acute and chronic lung
disease, central nervous system hemorrhage, and blindness. Long-term
outcomes can involve cerebral palsy, mental retardation, and learning
disability, and other forms of developmental delay.
--Approximately, three-quarters of neonatal deaths can be attributed
to preterm birth
--More than one-half of neurologic impairments found in children can
be attributed to preterm delivery
==========
So you can see, preterm births are a serious and growing problem in
the US. Data on preterm births is very well-documented, but
equivalent data on the incidence and outcomes of all preterm labor
episodes simply does not yet exist.
Before rating this answer, please let me know if you need any
additional explanation or information.
pafalafa-ga
search strategy: Searched Google, Pubmed, and offline medical
databases for [ "preterm labor" (incidence OR epidemiology) ] |
