What is preterm birth?
Preterm birth refers to the delivery of a pregnancy prior to its due date.
Because some babies are delivered prematurely because of maternal and/or fetal
complications, it is important to distinguish between indicated preterm birth
and spontaneous preterm birth.
In the strictest sense, spontaneous preterm birth refers to any baby
that is born more than three weeks prior to the expected due date. If you have
experienced a delivery or birth at less than 20 weeks gestation, this is considered
to be a miscarriage. Any delivery that occurs from 20 weeks gestation up through
36 weeks gestation is considered premature.
In order to determine whether or not a pregnancy has delivered prematurely,
it is important to accurately assign a gestational age. This can be accomplished
by following a woman’s menstrual history and calculating a due date based on a
known date for the beginning of her last menstrual period. Ideally, ultrasound
evaluation of the pregnancy, including measurements of the growing fetus, will
confirm the same gestational age that was calculated based on the patient’s last
menstrual period. However, in cases where the due date that is calculated by an
early ultrasound is different from the last menstrual period due date, the
ultrasound due date is generally considered most accurate.
What causes preterm birth?
When spontaneous preterm birth occurs at a very early gestational age
(between 20 and 32 weeks gestation) the most common identifiable cause is
infection or inflammation. In some cases, bacteria or viruses have caused an
infection within the uterus, vagina, bladder or some other part of the body that
results in preterm delivery. However, some cases of preterm delivery are the result
of an inappropriate or abnormal or inflammatory response by the mother to
relatively normal vaginal or cervical bacteria. Even infection or inflammation in
the gums of the mouth and around the teeth (called periodontal disease) has been
associated with preterm delivery.
Although in many cases of preterm birth, it is not possible to identify the exact
cause of preterm birth, a complete history - including information and details
about the timing and symptoms that were present at the time of a preterm delivery
in the past - may help. A detailed review of medical records that are available
may also help to pinpoint a cause of a previous preterm birth.
What is my risk of preterm birth?
It is possible by taking a thorough history and review of previous pregnancies to determine the exact risk or approximate risk of a recurrence of preterm birth. Several known risk factors have been reported for preterm birth, the most significant of which is a previous history of preterm birth. In a woman who has experienced one previous preterm birth in her last pregnancy, the recurrence risk for another preterm birth is approximately 35-40 percent. Other risk factors for early delivery include the presence of twins or triplets, fetal abnormalities that can result in excess amniotic fluid, known uterine abnormalities (such as an abnormal shape to the uterus or cervix), vaginal bleeding during the pregnancy and premature rupture of the membranes.
What are the risks for my baby if it is born too early?
Preterm birth and preterm delivery are the most common cause of neonatal death
and long-term complications including bleeding into the brain, blindness, deafness,
problems with the lungs, and problems with the intestines. The type of complications
that may be experienced by your preterm infant can only be determined by the exact
time of delivery and any other complicating factors that may have been involved
with your delivery.
In general, infants that are born very early are not considered to be “viable” until
after 24 weeks gestation. This means that an infant that delivers prior to 24 weeks
in a pregnancy will likely have less than a 50 percent chance of survival. Those
infants born before 24 weeks gestation that do survive will have a very high risk
of severe long-term problems as a result of their preterm delivery.
At 24 weeks gestation, in an otherwise uncomplicated pregnancy, the expected survival
rate ranges between 60 and 70 percent. Of those infants that deliver prematurely
at 24 weeks gestation and survive, about 40 percent will suffer some type of long-term
complication as a result of their prematurity. If a patient is able to remain
pregnant for as little as 2-3 weeks, the risk of neonatal death decreases
substantially as does the risk for long-term complications.
At 28 weeks gestation, in an otherwise uncomplicated pregnancy, delivery will
result in a survival rate for the infant of 80-90 percent and long-term complication
rate of only 10 percent among survivors.
By the time the fetus reaches 32 weeks gestation and delivers at 32 weeks gestation,
survival rates are as high as 95 percent and long-term morbidity is very low.
The long-term outcome for infants born after 34 weeks gestation would be the same
as those delivered at term. It is important to know that 34-week infants will likely
require some hospital stay as long as 1-2 weeks in the Newborn Intensive Care Unit,
but in long-term follow-up, these infants do very well and likely will have the
same outcome as an infant delivered at term.
Any infant that is born at less than 34 weeks gestation would be expected to spend
an extended period of time in the Newborn Intensive Care Unit, on average until 3-4
weeks before what their due date would have been.
If you previously experienced a preterm birth, you are well aware of the
complications and problems that are faced by premature infants. It is important
to note that in subsequent births, it is not necessary to completely prevent
preterm birth to have a major impact on the outcome of the infant. If we are
able to delay your delivery by as little as 1-2 weeks, there may be substantial
improvement in the outcome of the infant.
How can preterm birth be prevented?
This is a question that has been posed by many researchers and obstetricians for
many years. It is unlikely that any one intervention or treatment will prevent all
preterm births. This is due to the fact that preterm birth has multiple causes and
likely one treatment will not be adequate for the multiple causes that can exist.
Recent studies have shown that treatment with a hormone named progesterone
(a steroid hormone that is naturally produced by the placenta and by the mother
herself) can reduce the rate of preterm birth by as much as 30-50 percent.
The use of corticosteroids to hasten lung maturity and prevent other complications
of prematurity in infants that are at-risk for preterm birth has also been shown
to make a substantial improvement in long-term outcomes of infants. The timing
and route of delivery of the corticosteroids is something that must be determined
on a case-by-case basis.
There is substantial evidence to suggest that initiation of early prenatal care
and close monitoring may reduce the rate of preterm birth in some populations.
Early evaluation and consultation in a Preterm Birth Prevention Clinic will allow
you to initiate the interventions that are available in an optimal fashion and
will maximize the benefit of the potential reduction of preterm birth.
When should I be seen in the clinic?
Any person who is pregnant regardless of their risk of preterm birth should be seen ideally in the first 12 weeks of pregnancy. The first visit should occur between 10 weeks gestation and 18 weeks gestation to allow for adequate documentation of the estimated due date, a thorough analysis and physical exam to identify risk factors including risks associated with previous preterm deliveries and to detect the presence of inflammation or infection at this time.
What are the signs and symptoms of preterm birth?
The most common signs of preterm birth include the presence of regular uterine contractions. Some women describe these symptoms as severe menstrual-type cramps that occur in the lower part of the abdomen. Alternatively, intermittent tightening in the abdomen in a band-like fashion that begins in the lower back and radiates around to the anterior portion of the lower abdomen, has also been described. Other symptoms include vaginal pressure, change in vaginal discharge, and vaginal bleeding or loss of fluid. It’s not uncommon for women to experience preterm contractions beginning as early as 23-24 weeks gestation. However, when these contractions occur in a regular fashion (less than every 10 minutes) or occur in a frequency more than six contractions per hour, they should be evaluated, as frequently some intervention will be necessary. If you have had a previous history of preterm birth and you are experiencing regular uterine contractions, pelvic pressure, change in your vaginal discharge or vaginal bleeding or loss of fluid, you should contact your provider immediately.
Does Preterm birth run in families?
There is ample evidence to suggest that preterm birth does run in families. Women who were themselves born early are at increased risk of delivering their own infants early as well. Recent data has also shown that sisters and female cousins of women have experienced a preterm birth are at increased risk of having a preterm birth themselves. If you or a member of your family has previously experienced a preterm birth, please contact the clinic to allow us to assess your risk of preterm birth.
Are there any risks for the mother as a result of preterm birth?
Preterm deliveries are more likely to be the result of complications such as infection or abruption (a condition in which the placenta detaches from the uterine wall prematurely). These complications have implications for the mother as well. Mothers may experience significant infection that requires IV antibiotic treatment and in some may become life threatening.
Spontaneous preterm birth is more likely to require a cesarean section due to the fact that early infants often are found in breech presentation or some other abnormal presentation. Preterm babies sometimes do not tolerate labor well and are also at increased risk for cesarean delivery because of this as well.
Do I need to transfer my care from my regular obstetrician?
You are advised to continue your regular obstetric care and obstetric visits with your current obstetric provider. A Preterm Prevention Clinic may provide a detailed report to your physician outlining the risk factors and work-up and interventions that are recommended. If you were to participate in the Preterm Birth Prevention Clinic, you may make three visits during the time of your pregnancy. The first would occur from between the time of conception to 18 weeks gestation. The second visit would occur between 22 and 26 weeks gestation and the third visit would occur between 26 and 32 weeks gestation. Each of these visits is designed to screen for evidence of infection or other risk factors that may be associated with an increased risk of preterm birth.
Who should I contact if I have questions?
If you have a question or feel that you should be evaluated by a physician at a Preterm Birth Prevention Clinic, please see the directory of our research network or other links to find a physician nearest to you.
