Acog fetal dating, practice guidelines
With rare exception, if a first-trimester ultrasound examination was performed, especially one consistent with LMP dating, gestational age should not be adjusted based on a second-trimester ultrasound examination.
Clinical Considerations and Recommendations
Risk factors for post-term pregnancy may include primiparity and previous post-term pregnancy. Two strategies that may decrease the risk of an adverse fetal outcome include antenatal surveillance and induction of labor. In College girl dating a high school boy post-term women with unfavorable cervices, both labor induction and expectant management are associated with low complication rates and good perinatal outcomes.
Options for evaluating fetal well-being include, nonstress testing, biophysical profile BPP or modified BPP nonstress test plus amniotic fluid volume estimationcontraction stress testing, and a combination of these modalities. Although evidence shows that antenatal fetal surveillance for post-term pregnancies does not decrease perinatal mortality, it has become a common, universally accepted practice.
Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; therefore, decisions need to be guided by careful consideration of the entire clinical picture and may require close surveillance, including repeat ultrasonography, to ensure appropriate interval growth.
Physician Guidelines & Reports
Fetal Imaging Workshop Invited Participants. For instance, one study found a reduction in the need for postterm inductions in a group of women randomized to receive routine first-trimester ultrasonography compared with women who received only second-trimester ultrasonography 5.
There is conflicting evidence as to the effectiveness of sweeping the membranes at term in reducing post-term pregnancy.
Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as the biparietal diameter and head circumference measured in transverse section of the head at the level of the thalami and cavum septi pellucidi; the cerebellar hemispheres should not be visible in this scanning plane the femur length measured with full length of the bone perpendicular to the ultrasound beam, excluding the distal femoral epiphysis the abdominal circumference measured in symmetrical, transverse round section at the skin line, with visualization of the vertebrae and in a plane with visualization of the stomach, umbilical vein, and portal sinus 8 Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role.
Many practitioners use twice-weekly testing with some evaluation of amniotic fluid volume beginning at 41 weeks of gestation. Post-term pregnancy is associated with risks to the fetus, including increased perinatal mortality rate, low umbilical artery pH levels at delivery, low 5-minute Apgar scores, dysmaturity syndrome, and increased risk of death within the first year of life.
Last menstrual period versus ultrasound for pregnancy dating. Conceptional age, menstrual age, and ultrasound age: Because decisions to change the EDD significantly affect pregnancy management, their implications should be discussed with patients and recorded in the medical record.
The information should not be construed as dictating an exclusive course of treatment or procedure to be followed. 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.
A comparison of recalled date of last menstrual period with prospectively recorded dates. Delivery should be effected if there is evidence of fetal compromise or oligohydramnios.
The authors add that, because of ethical and medicolegal issues, no studies have included post-term patients who were not monitored. For example, for Acog fetal dating day-5 embryo, the EDD would be days from the embryo replacement date.
When should antepartum fetal testing begin? Post-term pregnancy is defined as a pregnancy that has extended to or beyond 42 weeks of gestation days, or estimated date of delivery [EDD] plus 14 days.
The risk of adverse sequelae may be reduced by making an accurate assessment of gestational age and diagnosis of post-term gestation, as well as recognition and management of risk factors.
Obtaining an accurate EDD using ultrasonography early in the pregnancy can reduce the incidence of pregnancies diagnosed as post-term and minimize unnecessary interventions.
Recommendations The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine make the following recommendations regarding the method for estimating gestational age and due date: Because of limited evidence on the safety or efficacy of vaginal birth after cesarean delivery after 42 weeks of gestation, the authors make no recommendation for its use as an alternative to elective repeat cesarean deliveries for some women.
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.
Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Placental sulfatase deficiency, fetal anencephaly, and male sex have been associated with prolongation of pregnancy, and genetic predisposition also may play a role.
Methods for Estimating the Due Date
A consistent and exacting approach to accurate dating is also a research and public health imperative because of the influence of dating on investigational protocols and vital statistics. Labor usually is induced in post-term pregnancies in which the cervix is favorable because the risk of failed induction and subsequent cesarean delivery is low.
For instance, the EDD for a pregnancy that resulted from in vitro fertilization should be assigned using the age of the embryo and the date of transfer.
What is the role of prostaglandin preparations in managing a post-term pregnancy? A Cochrane review concluded that ultrasonography can reduce the need for postterm induction and lead to earlier detection of multiple gestations 6. Choose a single article, issue, or full-access subscription.