Dating ultrasound for amnio
Post-term pregnancy is defined as a pregnancy that has extended to or beyond 42 weeks of gestation (294 days, or estimated date of delivery [EDD] plus 14 days).
The reported frequency of post-term pregnancy is approximately 7 percent.
Most cases of post-term pregnancy result from a prolongation of gestation.
Because of normal variations in the size of infants during the third trimester, dating the pregnancy during this period is less reliable.
If the estimated gestational age by a patient’s last menstrual period is different from the estimate obtained via assessment with ultrasonography, the ultrasound estimate should be used.
Post-term pregnancy is associated with risks to the fetus, including increased perinatal mortality rate, low umbilical artery p H levels at delivery, low 5-minute Apgar scores, dysmaturity syndrome, and increased risk of death within the first year of life.
Although post-term infants are larger than term infants and have an increased incidence of fetal macrosomia, there is no evidence to support induction of labor as a preventive measure in these cases.
Risks of post-term pregnancy to the pregnant woman include an increase in labor dystocia, an increase in severe perineal injury related to macrosomia, and a doubling in the rate of cesarean delivery.