Preterm Birth
Babies born before 37 completed weeks of pregnancy are called premature. In Ireland the incidence of premature delivery is approximately 7%. Preterm births can also be subdivided according to the gestational age at delivery: the minority (approximately 5%) of all premature births occur at less than 28 weeks' (extreme prematurity), about 15% at 28-31 weeks' (severe prematurity), 20% at 32-33 weeks' (moderate prematurity) and 60-70% at 34-36 weeks' (late preterm delivery). The more immature the baby at the time of delivery the greater the risk of death or long-term developmental problems.
Broadly speaking the cause of preterm delivery can be grouped as follows: Spontaneous preterm labour with intact membranes (about 40- 45%), spontaneous labour following Preterm Rupture Of Membranes - PROM (about 25-35%) or delivery that is indicated in the maternal or fetal interest (about 25-30%).
There are many reasons why a mother might delivery early. There are ethnic differences e.g. Spontaneous preterm birth is most commonly caused by preterm labour in white women, but by PROM in African American women. The mechanism of preterm labour is complex with the most recent research suggesting that intrauterine infection is a frequent and important cause leading to preterm birth. The infection process involving amniotic fluid and membranes surrounding the baby results in activation of the body's own natural responses resulting in uterine contractions and preterm labour. Cervical incompetence caused by congenital cervical weakness has been implicated as a cause for some preterm birth. However, in many cases the exact cause cannot be determined. There are certain known risk factors for preterm delivery including women who have had a previous premature delivery and women who are carrying twins or triplets. Multiple gestations will result in preterm delivery as a result of uterine overdistension, resulting in contractions and PROM. Vaginal bleeding caused by placenta preavia or placental abruption is associated with a very high risk of preterm delivery. Certain medical conditions during pregnancy also may increase the likelihood that a woman will have preterm labor. These include preeclampsia, maternal diabetes, thyroid disease and urinary tract infections.
