The length of a normal pregnancy is 40 weeks (10 lunar months) from the date of conceptions. Any infant born prior to the 37th week of pregnancy is considered to be premature and may be at risk for complications. Many problems associated with prematurity depends upon how early the infant is born and how much it weighs at birth. Early prenatal care is critical to determine an accurate EDC (estimated date of confinement) or “due date”. The most accurate way of determine the gestational age of an infant if the LMP (last menstrual period) is irregular or the patient is unsure, is to use ultrasound imaging to measure the “crown-rump length” in the first trimester. Ultrasound can be used for dating a pregnancy only until approximately 18 weeks gestation. After 18-20 weeks, the fetal weight is calculated by “averages” and will vary from patient to patient and can be affected by factors such as genetics, maternal disease (diabetes, hypertension), maternal nutrition, or maternal smoking or substance abuse.
There are many reasons why patients require premature delivery. The most common reason for preterm delivery is simply premature labor unresponsive to medications designed to slow contractions of the uterus. Other medical reasons for preterm birth are preeclampsia, maternal heart or lung disease, infections of the amniotic sac, uterus or cervix, premature rupture of the membranes (sac around the baby), or even a fetus with a genetic anomaly. Doctors carefully consider all options before making the decision to delivery any patient prematurely. This delivery would result in a “preemie” infant requiring specialized and costly care.